740 Harness Failure and Flameout Notes                                                                                                                                           Sept 2010  R. Kwas 


Background:  Vehicle:  1990 745 B230FT +18X,XXX Miles.  The car runs fine but at reduced HP…turbo spins freely and without contact noises, but makes no boost…I suspect a (partially) bypassing wastegate which is preventing the exhaust turbine from spinning up fully, causing this.  Without boost, the car is somewhat of a roadslug…just what a beginning driver should get his first driving experience with!  I’ve promised son Nick that if he can drive a year without incident, we “will see” about getting the turbo functional again (and giving him 50 more HP)! 


Previous Related Work: 

  1. Installation of new Brush assembly into Alternator after wear-out of old (not too many thousands of miles ago). 
  2. Replacement of Starter motor assembly, (several years ago).


Recommisioning Vehicle for Nick

  1. New Battery installed - supercleaned all battery connections and reconnected with Anti-Corrosive Zinc Paste (ACZP).
  2. New exhaust system installed by (European Motors)
  3. Replaced two power steering hardlines after rust-through and leakage which caused total loss of fluid.  (EuroMo)
  4. Replaced steering u-joint which was found to be partially frozen during lowering of steering rack.  (EuroMo)
  5. New brake discs/pads all around, one new rear caliper.  (EuroMo)
  6. Tightened Alt drive belt.


One week after recommissioning vehicle and several days of problemless driving (including highway…it does get up to speed, but with a calendar), Nick reports several control indicators ON after immediately after starting, also idle, and throttle difficulties.  Owner’s manual explanation of this combination of indicators is:  Charging System Failure

Upon initial inspection under the hood, alternator, battery and starter wiring are tight and normal looking, but the sizable alternator output wire, where it leaves harness to connect to starter stud and heavy battery wire, exhibits severe heat damage…its insulation is completely cooked off and the sizable conductor has fused open!!!…the insulation of several other small gauge wires in the immediate area is also completely carbonized and crumbles from the conductors when touched.  Insulation of four wires ending at Throttle Position Switch is also completely carbonized and crumbles off easily when touched. 


  First discovery and views of damage area.   A number of wires have had insulation completely burned away.  Heavy wire coming out of sleeving with red (Battery +) wire has gotten so hot as to obscure its color!  A large copper oxide bloom is visible on one wire…?


During initial inspection, touching these wires and their carbonized insulation crumbling off, causes the solenoid control wire to become energized and starter to be activated spontaneously and continuously.  An immediate Emergency Disconnection of the battery stops this action.  Battery remains disconnected after this. 


Initial Conclusion:  Excessive heat has clearly caused extensive damage to wiring just ahead of the starter.  Starter itself and heavy wiring to starter is tight and not discolored, but a lot of insulation has crumbled off Green wire which is the Solenoid control wire, back where it exits the harness.  This wire coming into contact with the remaining live end of the Alt wire caused the spontaneous activation of starter.  After taking stock of this general condition I look around a bit more.  There are several strings of black soot lying on top of the intake manifold…I am looking at the aftermath of a serious fire event here!


In trying to determine when, and maybe under what circumstances, this event occurred, I try to get some details…Nick reports that he did not run the starter for an extended time (my first thought for a cause of high heat in the starter area), he did not smell any burning wire smell at any time (where there’s smoke, there’s not only fire, but also distinctive stink), and that the indicators to show Charging System Failure were not lit, and that he had no particular throttle or idle issues when he last drove the car and parked it the previous day…so it can only be concluded that the insulation was finally compromised and the actual burning and entire damage occurred between the time he had parked it in the evening and before he started it the next day...I just wonder how close we came to having a flaming external combustion engine Volvo in the driveway in the middle of the night(!)…and this certainly makes the point for all the materials needing to be “self-extinguishing”. 


Detailed Trouble Investigation Findings:  Careful removal of Idle Control Valve (ICV) along with its mount and hoses to gain access, reveals one of its rubber hoses (the one which runs to intake manifold), where it passed by the area of apparent heat concentration has a thumb-sized hole burned in (this vacuum leak would certainly explain the idle/throttle difficulties experienced after the most recent start.).  Wires to ICV have virtually all insulation burned off and connector at valve has been subjected to enough heat that it is melted to mating connector and needs significant force to be separated from it.  This area must have been alight with the flames traveling up the harness! 


  ICV removed from vehicle, showing severely burned airhose, and connector.  All Insulation has been burned from wires of connector and connector itself is melted and pretty much unified with its mate on the valve.


The bracket which mounts ICV and harness clamps is also removed to gain access and an unobstructed view of the main harness junction, where alternator output wire exits, TPS wiring exits, and injection wiring all meet. 


Further Inspection and Possible Root Cause and Failure Scenarios:  Once harness can be moved around a bit for inspection of the area, it becomes clear that alternator output wire has indeed fused completely open in the area where it passes over chassis wire, where this wire is connected to engine block (this would certainly explain a Charging System Failure indication) after next starting attempt.  The Alt output wire conductor has apparently made contact with the conductor of the engine grounding wire (although both wires are securely located by clamps, and the harnessing practice is quite good with rubber insulated clamps locating the over-sleeved harness in 6 inch intervals, I have trouble imagining that there was enough vibration and displacement of insulation between the two crossing wires, that they finally made contact…but the fact that a contact occurred is incontrovertible from the remaining evidence!)…maybe what little vibration was possible, exacerbated by elevated engine compartment temperatures was enough after 20 years and nearly 200,000Miles, that it really did happen…in any case, once the contact occurred, Fire, Smoke, and Brimstone took over…the presence of copper meltballs on both wires pretty much confirms this as the ground-zero!  (…and Copper melts at 1984°F…I looked it up!)


  Yellow:  Copper meltballs on both motor grounding wire and Alt output wire at point of contact, are evidence of heat way beyond red-hot!  Violet:  Ends of fused open Alt output wire, showing heavily corroded starter side of open.  A significant copper oxide bloom right at the starter side of break in Alt output wire is apparent.


After considering the evidence left behind, particularly trying to reconcile that copper oxide bloom…a second possible Root Cause comes to me:  The significant quantity of green copper oxide located coincidentally (and suspiciously) right at (the starter side of) the break in the Alt output wire, makes me think of another possible root cause…that corrosion (caused by ?unknown? at this time) decreased the current handling capability (conductor cross-section) of the Alt output wire so severely, that it heated (due to I2R dissipation), and this, not vibration, compromised the insulation (wire and protective over-sleeving), which eventually allowed it to make contact to the grounding wire which unfortunately and as luck would have it was also located right there (and the final failure and contact occurred after vehicle was parked, given lack of symptoms that would have been impossible to overlook if engine had been running, with a driver in the vehicle), at which time, ultra-high current supplied by the battery flowed, causing arcing and massive amounts of heat…, the available energy was easily sufficient to fuse the 8ga. wire open totally(!)… but until that happened, there had been enough thermal energy released to charbroil everything in the immediate area!  


ROOT CAUSE:  The coincidence of an energized wire with insulation compromised by internally generated heat as a result of corrosion, in a location where it was able to make electrical contact with a chassis wire. 


There is little other evidence left after the subsequent Fire, Smoke, and Brimstone event, but I am (and remain) totally convinced that this scenario must be the Root Cause of the damage because of the very odd, unusual, and totally unexpected presence of significant amounts of the copper oxide (it is reminiscent of what an acid exposed battery cable would look like after a prolonged time of allowing the acid to convert the copper to green dust!) in an area which would normally have been inside the insulation in the middle of a continuous run of wire, doubly protected by its own insulation, and also the over-sleeve.  


Engine grounding wire (which is definitely a bit heavier in gauge of the two) remains intact, but copper meltballs are evident on this wire in the exact location where (energized) alternator output wire crossed it and the contact occurred.  This is clearly the source of the heat, which went way beyond red hot to cause the meltball evidence! 


  Comparison of fused Alt output wire and replacement harness held in same orientation so location along wire of the inadvertent contact is confirmed as being at a location which would have been inside the oversleave and triple insulated normally!


  Closeup of wire strands from fused area, including two uncorroded strands (Yellow) for comparison.  Surface corrosion and inter-granular corrosion and embrittlement are apparent at all wires in failure area.  A significant decrease in diameter (Red) is consistent with corrosion having been at work for a long time, and this condition is apparent to some extent at all of the conductor strands in the area.


 Microscopic pic of corroded wire.  


Analysis of Circuit and Action after Inadvertent Contact of Engine Ground and Alt Output Wires:  In terms of energy source for this short to chassis, the Alt output wire is energized from one end by alt (but only when engine is turning and alternator has an output), to the maximum output of the Alt (80A, so about a kilowatt!), and since it is connected to stud at starter to which heavy gauge wire directly from battery is also connected, it is also always connected to battery power from the other end also which is capable of supplying well in excess of 100A if the circuit resistance is low enough (so easily multiple Kilowatts of power!).  As this is all unfused high current wiring, it would explain why the massive heating which occurred to cause the extensive incidental thermal damage was allowed...there is just no overcurrent protection anywhere in sight on this circuit…it kept making mega-heat and only stopped after the wire involved burned open and the circuit to the battery was broken…if fact, the battery didn’t even discharge fully supplying this energy…indeed, it had sufficient charge remaining after the event to start the engine! 


Damage Inspection:  Sleeving and taping of harness in the damaged area is carefully cut back to allow inspection back into the harness to ascertain the extent of damage…several small gauge wires are either burned open or so brittle that they tear apart when handled…wiring is carefully separated and all damaged wires and components are inventoried.  Using color codes, which are still intact and clear outside the immediate damage area, and process of elimination, it is possible to inventory and account for all wires in the area, including the most heavily damaged ones. 


List of obviously damaged items: 

Alt output wire. 

TPS wiring including melt damage at connector 

ICV wiring including melt damage at connector. 

ICV rubber hose. 


List of possibly incidentally damaged items: 

ALT  (from having a high current short to chassis.) 

TPS  (from having wires inadvertently energized.) 

ICV  (from having wires inadvertently energized.) 


[I post initial findings on Brickboard 700 Forum.]


LINK:  http://www.brickboard.com/RWD/volvo/1430307/740/760/780/major_electical_harness_damageseek_source_used_fi_connectorswith_cables_idle_control_valve_tps.html


I also relate my findings to Ted the local independent Volvo specialist [European Motors, Park Road W. Hartford CT], who is impressed by the level of damage, says that this is indeed a rare event, and who checks his stock of used parts and pieces and comes up with a used FI harness (which was cut from its donor vehicle) including IVC with hoses:  My intention is to harvest the TPS and ICV wiring from this harness, splice it in, to replace the toasted wiring (solder and heatshrink tubing technique will be used for absolute reliability and confidence in the spliced repair-connections). 


I do not even consider “replacing the entire harness” (which was naturally one of the first recommendations to my Brickboard posting).  Thanks for the helpful advice, but replacing the limited number of damaged wires cleanly is infinitely preferable to me, compared to the massive manipulations and the risk of insult to existing components and connections that replacing an entire harness would require!  The intent of my post was really to find out if this failure might be due to a well-known chronic problem (ala contaminated solder joint in the Radio Suppression Relay). 


The plan is to repair all damaged wiring which can be found by inspection, then assemble everything with PVC sleaving, using best harnessing practices, and I would especially assure the ground and Alt wires have either a confirmed airspace or that they are fastened together and motion(and contact)-less forever.  The fused open and corroded Alt output wire will be totally replaced, not spliced and repaired, and I may add a 100Amp fuse in series with battery as is typical of some vehicles (although that would have been downstream of the heat-source and short, so would not have prevented the meltdown).  


The damaged ICV hose will be replaced, as will the top radiator hose (it was noticed this hose was close to failure while under the hood). 


Harvesting Replacement Connectors and Preparation for Installation:  The three-pin connector for TPS and two-pin connector for ICV (called Air Control Valve [ACV] in the manual) are cut from donor harness leaving maximum wire.  Color code inconsistencies are noted, but these are explained by possible variations in wiring (dotted connection lines in Haynes Manual wiring diagram).  The TPS connector actually only has three wires connecting to two pins in the donor harness, so a spare wire with crimp must be also harvested.  The quality Bosch connectors have a typical crimp-pin with retention barb arrangement…a pin extraction tool (dental style pick) to allow removal is quickly figured out, and used to extract one pin with (White/Red) wire without damage to pin.  This pin with wire will be reused to provide connection to pin number three on TPS connector.  


Notes on Repairs: 


.  Solenoid control wire.  The damaged wire is cut back to a clean undamaged point, stripped, and soldered to a repair wire (same GREEN-BLUE color code) with a lineman’s splice.  Double heat-shrink tubing finishes and protects the joint neatly for a permanent repair. 


TPS wiring:  The four wires are similarly repaired, one at a time, and terminated to the harvested three-pin TPS connector. 


TPS Conn Pin

Color code


Grey / Red




Orange (two wires into one pin)


Questions of ICV polarity:  Because insulation of the wiring to ICV was completely burned away, the color codes given for its connections are not consistent with those found on the car.  It seems to me that I must verify the polarity of the hookup…


For repairs, I will use the used ICV which has an undamaged connector.  Checking the action of the valve reveals that it is NOT polarity dependent.  9V applied in either direction opens the valve…so polarity is NOT critical, but wiring is replaced by lengthening damaged wiring and terminating to the same pin number on connector in any case.  Changes in color codes are recorded here.


ICV Wiring:  The two wires are similarly repaired, one at a time, and terminated to a used two-pin TPS connector.  The color code of wiring found on vehicle does not match that given in the Haynes manual so a change is made. 


ICV Conn Pin

Color code (Vehicle)

Color code (Connector)









 Violet circle - end of sleaving of TPS harness.  Turquoise circle – end of sleaving of ICV harness (note color changes). 


  Splicing and heat-shrinking of all low current wires is complete. 


  High current engine block negative wire with damaged area. 


High Current Wire to Engine Block (passes Starting Current) from Battery Negative:  Upon closer examination, this wire (refer to graphic, B) had lost more than half of its cross-sectional area (therefore current handling capability in the same way the Alt output wire did due to corrosion!) in the arcing event.  Initially I had thought a parallel heavy wire from block to the chassis might be a sufficient repair, allowing the two conductors to “share” the high starting currents, but then had second thoughts…  A repair wire (D) was made up using 10ga. and installed with the intent that the damaged wire and new wire would share the starting current…and they would, but looking at it closer, and because of the insufficient cross-sectional area remaining in the wire (B) decided against installing it as the only repair, leaving the heavy wire damaged…I decided to repair the damaged heavy gauge wire as well.  


  High current repair wire E with crimp on one end and high current, split-bolt compression clamp (F) allows permanent repair connection to existing wire, on the other. 


The repair would be implemented with a heavy-duty splice.  A 4ga. welding wire (E, fine strand welding cable - which doesn’t mind being bent, even in sharp radii, and can easily put up with a lifetime of service in a high-vibration installation) is prepared with a crimped connector by a helpful plant electrician (thanks Matt!).  The block end of damaged wire (B) is unbolted and wire is cut back to a clean area where a repair conductor can be joined to it.  Home Cheapo supplies the quality, high current, split-bolt compression clamp (F) which will join the repair and existing wires perfectly.  The crimp gets an ACZP treatment and taped, and compression clamp and bare wires into it get a generous blob of ACZP as well before installation…I expect no issues with the high current wiring, given this repair and improvement!


Figure 12.  High Current repair wire


FIGURE 13.  High current wiring. 
(E) Repair wire replaces damaged area of original wire.

High Current Wiring:

A.  Carries starting current (Battery Pos)
B.  Carries starting current, (Battery Neg), Cross section is reduced by damage at RED.
C.  Carries all current running through Chassis, but no starting current.
D.  Added 10ga. wire.  It can be seen that this path in combination with Wire C is effectively in parallel with Wire B, therefore will share starting current after being added.  Wire D also establishes another connection between Engine and Chassis (certainly one already exists elsewhere, but adding another can only help and never hurt).
E.  Repaired Section of Wire B (GREEN) has increased cross-sectional area from original. 
F.  High current split-bolt which joins repair wire to existing (lathered up with ACZP naturally, then taped and forgotten!). 


  High current repair wire installed, taped and tie-wrapped to new “D” wire.  Routing of engine block negative wires after repairs is nowhere near harness containing other wires. 


ICV Installation:  Once all repairs to harness and high current engine block wire is complete and satisfactory, the ICV is installed onto its bracket, and its hoses are connected (all clamps have naturally been prepped with anti-seize for smooth action).  Access is very limited to things behind there after that…


Repairs are complete, harness clamps are installed.  !


Prestart Check:  All repair work is triple checked, ICV and TPS connectors are confirmed installed and seated, harness is checked for being fastened, a few more wire ties are added in strategic places to prevent chaffing, oil is checked, cooling system is topped up…there’s no putting off the First Start any longer!


First Start after Repairs:  The battery is charged overnight, then (loosely) connected (for the first time in two months!)…nothing exciting happens (in this case, Good!)…the key is inserted…nothing extraordinary is displayed on the instruments…the key is turned to the Ignition ON position (fuelpump is heard as it pre-charges fuel rail for two seconds)…then turned to Start position…  After about 3 seconds of cranking, the engine starts normally and settles to a 900 RPM idle…so far, so good…the engine also responds normally to blipping the throttle…that’s great too…we end the session and disconnect the battery…more tomorrow…


First Drive after Repairs:  I drive the car to work figuring to shake down any incidental issues which have not yet been discovered.  The ride to… is uneventful, as is the ride back home.  Can it be this easy? 


Well, not quite…lifting the hood for a visual double check however, reveals some coolant leaking from around the radiator top hose…it seems that where it is clamped over the “plasdick” stub of the radiator has some damage where it is clamped on…I don’t think I overtightened it breaking it, but that is what seems to be the case…luckily there is enough stub there to allow the hose to be clamped on for a good seal.  I am seriously considering replacing the radiator with an all-metal one…


Wrap-Up, and Conclusions:  Nick has now driven the car for a week+ with no complaints or new, related issues coming up.  The idle does seem to be a bit high (at 1100)…so there seems to be some issue possibly related to the ICV, but the car has since gone through and passed the state emissions test, so I don’t suspect any vacuum leaks which would allow ingested “false air” to result in an incorrect mixture, which would certainly cause a failed emissions test (I’m tempted to install the old ICV for some comparison tests). 


Aside from that, it would seem that the damage was limited to that which was able to be found by examination.  Having repaired that and having no further issues, I have to conclude, that no additional, incidental damage had occurred (phew!!)…the obvious damage was certainly enough!  I am (still) convinced that the corrosion compromised Alt output wire caused the problem as I suspected.  I see no possible other explanation or scenario for the evidence which was left behind, and this scenario is consistent with all evidence found.  That still leaves the question of how and why the conductor would get a corrosion causing agent on it under the insulation…it’s unlikely I will ever get the answer for that question.


Nick puts in some sweat equity.


Finally, the (dirty)hands-on time spent with Nick the 17year-old was a pleasant, productive, and unusual time, so I can only be thrilled by the successful outcome…it would have been difficult to justify the time and effort with him if the outcome had not been so good! 


Follow-up:  Nick has been driving the car now for two months, it has been reliable, and served him without issue…he has actually said he “likes the car” …and that with a pretty lethargic unboosted 2.3L…I don’t believe he has said he loves it just yet…that may have to wait until after we get that turbo making boost again…watch this space!


Legal notices:  The term Volvo is used here for reference only.  I am not affiliated with Volvo…although I do also Roll….  When did jungles become rainforests?  When did Personnel become HR?  I have used the procedures and advice presented here in practice many times myself but they are presented strictly as a guide...your results may vary...and you are responsible for your own actions and knuckles!  It’s a car, not a phonebooth!  If you lived here, you’d be home by now, blah, blah, blah…

The contents of this article are Copyright © 2009 by Ronald Kwas.  You are welcome to use this article and its contents for non-commercial purposes.  But if you copy and republish it, whole or in part, without giving credit to the author, or linking back to the Sw-Em site as the source, you’re just a lazy, scum sucking plagiarist!  Go work for the Washington Post or something!  


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