Electrical Upgrades Considered  
Mar 2015 R. Kwas

Control Relay
Headlights ON Reminder Beeper


General:  Whenever adding anything electrical to a vintage Volvo, there are several factors which should be considered: 

1.  How much power will the device consume?  (This will determine gauge of wiring needed.) 

2.  Does the new device need power all the time (Battery Power), or when Ignition is ON (Ignition Power)?  (This will determine what source circuit and location to draw power from.)


Negligible Loads (up to 5W)GPS, Cell Phone, Buzzers and Beeper,

No system modification are called for.

Minor Loads (up to 50W):  Audio System of Modest power,  

No system mods are called for, but Load should be on a fused circuit (either an existing one or a new one).

Substantial Loads (over 100W):  Driving/Fog Lights, Monster Audio Systems (Beware:  Some consume monster stand-by power when they're not even ON!)

A Control Relay and proper wiring (taking into account the entire new current path) including a protective element, are called for.


Headlights: If the Wattage rating of Headlight elements is not increased, no increase in wire gauge, or addition of Relays is necessary.  This is often discussed, but just not necessary (see Sw-Em Tech ArticleLighting, Relay Controlled Headlights)...one could do a lot more for the brightness of the headlights, by bringing all electrical connections back to as-new condition.  See Sw-Em Tech Article Voltage Drop in Headlights Power in Hex Connectors

Auxiliary Lights:  Substantial additional loads to a vintage Volvo Electrical System should not be powered by the existing wiring...and the additional load current should not be run through the vintage switches, so when adding things like auxiliary lights, the proper way to wire these is to use a relay to control the high current.  The modest coil current of the control relay may be added to the vintage switch. 

K1 shown below is slaved off the Ignition Switch, so the Ignition Switch is subjected only to a modest additional current...no problem! 

(Not shown) A relay could also be slaved off the Light Switch for control of Driving Lights for instance.

Link to Relay Slaved off Ignition Switch:  Ignition Slave Relay


Generic circuit for correct control of additional Loads

Note:  This is a generic diagram which can be modified!  Circuit shown includes a Chassis Connection Relay (K2) necessary for a Headlight On Reminder, and an Ignition Power Slave Relay (K1) which is recommended when adding high power loads to a vintage Volvo.  Shown are 5 Terminal relays which have a high power contact (87a), closed when Relay is unenergized.  If there is no interest in supporting any Loads during Ignition OFF condition, a 4 Terminal relay (without 87a) could be used.  Battery Power can typically be taken from the Solenoid Terminal 30.

Do not use 3 Terminal relays as these have an internal connection between high power and coil, so do not allow separating control and high power circuits.  This means high Load current would still have to flow through Ignition Switch contacts...and that would defeat one of the major circuit advantages of adding control Relays.  Added in the manner shown, current flowing through the existing vintage Ignition Switch contacts is increased by only a modest amount, and heavier than stock ga wire can be used for minimum voltage drops along the way, resulting in best voltage at load.

Link to an example of a three terminal relay circuit - the recommended Horn upgrade (before, Horn circuit current is not controlled by a relay).  Relay power circuit cannot be separated from Load circuit.  Power supplies both relay and load. 


Buzzers and Beepers                                                                                                   

Electrical notes for installing Beepers and Buzzers 

There are very few times that I want my vehicle to nag me with beeps, buzzes, voices, or any other annoying noises (my phone does enough of that already), but one of those times I allow my vehicle to do this is when the engine is running, and has no OIL pressure.  On a P1800 for instance, with its Oil Pressure gauge, one wouldnít know of a loss of oil pressure unless one was looking at the gauge (or maybe hearing unusual noises from the engine compartment, but thatís already too late!)...so on my 1800, I have added a standard oil pressure switch and a beeper.  Yes, it does sound off when IGN is ON and before motor is started and running, in the same way that the OIL Indicator lights in a 122 before start-up...but I donít mind...before start-up is test-time of the on-board sensing and indicating systems. 

Headlights ON Reminder Beeper:  Another condition which do want my vehicles to nag me about, is lights left ON with engine OFF, because this load is certain to drain the battery within hours and prevent starting.  Presented here, is a circuit diagram for the absolute simplest circuit which will do this.  It powers the audible indicator of your choice from the Light Switch, and completes the low side circuit to battery negative with a new relay which needs to be added (and which provides an IGN OFF function that is otherwise not available in these vintage vehicle systems).  This relay is a standard, low-cost ďForm ďCĒ type (Bosch No. 0 332 209 150, 5 Terminal or similar), wired to provide a closed contact, and connection to chassis (only) when IGNition is OFF, by way of the N.C. contact 87a. 

I developed this Ultra-Simple (and low cost) Lights On Reminder Circuit on the request of a 122 owner.  Link to Thread:  http://www.brickboard.com/RWD/volvo/1266780/120-130/headlight_buzzer.html

It could certainly be used for other vintage Volvo vehicles.  The design locates the new relay under the hood where it can be wired to pick up fused IGN power, routes a single control wire through the firewall, and locates the audible indicator under the dash where it can be heard and also simply connected to the lights switch. 


Additional Information... 120-130 1966

...the circuit shown is actually different from the earlier verbal explanation (so disregard!)...after thinking about it, I changed it a bit and made it as simple as possible, locating relay under the hood, powered by the Fuse 2 circuit (or Fuse 1 if there is an empty terminal available), and included a single wire routed through the firewall, to the beeper/buzzer located under the dash somewhere...the standard BOSCH form C relay (inexpensively available, with a Normally Open NO AND a Normally Closed NC contact) is powered when IGN is ON. At that time, ground is removed from Neg side of beeper, so if lights are turned ON, beeper will not sound. With IGN OFF, low side circuit of beeper is completed to chassis, so if lights are also turned ON, power is supplied to beeper high side and it will sound...simple!

Use in conjunction with 122 wiring diargam: http://www.sw-em.com/122S%20Wiring%20Diagram.jpg



Things I donít wish to be nagged about include...an open door...I KNOW, I opened it!...and the fact that I havenít put on a seat belt...Iíll be in charge of when I use them and when not...beep your a** !

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