SwEm Technical Bulletin Number 4 
Original posting:  Mar 2013

Attention:  All pre-'69 P1800 Owners:

Replace Fuse 3, specified at 35A, with an 8 or 10Amp rated fuse (Type 3AG)! 

The manual calls for, and Wiring Diagrams show, a 35A* rated fuse in the Fuse 3 location...that's the single fuse holder located on the electrical panel in the engine compartment, as shown below.  

Fuse locations at Yellow, on electrical panel of 1800 models. 

This value fuse was specified with the same high current rating as the Fuse 1 and Fuse 2 (more on this below!), and without going into why and 1800 has only three fuses in the first place, it is a fact that the Marker light circuit which Fuse 3 protects (that's it!!!) actually sees just over 4A as a normal operating current!  With a 35A fuse installed, a fault current sufficient to cause wiring damage would be allowed to flow! 

This really questionable design decision may be explained by the fact that it was at the time, a cost-saving measure by the harness manufacturer Lucas (insert choking sounds here!) or some subcontractor.  They would only need to stock one value fuse instead of different values, but if 1800 owners are concerned with truly protecting their electrical system from damage which can be caused by a fault-current (and that IS the point of fuses!), one should change Fuse 3  to an 8A or 10A rated fuse at the next opportunity! 

See also:  Proving Everything Bad you Ever Heard About Lucas  ...an objective study to support these recommendations, and underscore all the anti-Lucas slurs ever uttered!

For more detailed see:  Fuses, Allocation and Troubleshooting.htm#1800_(P_S_not_E_or_ES) 

*  BEWARE! This is a British Fuse rating for the current at which fuse will open.  When replacing Fuses 1 and 2 in an 1800 with American rated fuses, replace with 3AG type17A continuous current rating (or 20A if 17A rated ones are not available).  NEVER, EVER, EVER with American fuses rated at 35A.  See more about that here:  British vs. American Fuse Rating