Triumph Repair: Spitfire 1500 Electrical, radio melted insulation relay lucas gremlin

Question
Hi, I have a 1975 Spit and I recently had a radio installed. Ever since, the car has been having strange electrical issues. There is now a parasitic drain on the battery. I have since installed a cutoff switch on the battery. No big deal, but last night, I was pulled over by a cop because my tail lights were out. When I got to my destination, I found out that I blew the center fuse. Could that be related to my radio? To my understanding, the radio runs on the top fuse. Also, I am getting a fasten seatbelt alarm when I am wearing my seatbelt which leads me to believe that I have a short somewhere. Do you have any suggestions on how to correct the issues?

Answer
You could pull the radio out and make sure that the wiring isn't grounding out someonewhere.  Maybe the power of the radio is greater than the stock unit, and the current draw is more than the insulation can handle.  Trace the +12 and ground wires for the radio back to the ignition switch and wherever the radio is grounded.  Insert a relay to the ignition circuit, and wire a dedicated +12 thick wire to power the radio, such that when the ignition is on, the radio is drawing directly from the battery, through the relay and thick wire, and not the ignition switch itself.

However, It may be too late for that to make a difference.  You may have now melted the insulation somewhere, and now you have been visited by the well-known Lucas electrical gremlin.  Just about every single brit car I have had, has needed a new wiring harness or a major rewiring.

Most parasitic drains like you describe are rarely grounding out to the chassis, but are rather grounding between wires in the wiring harness.  This is usually from a section of the wiring overheating and melting the insulation.   This is nearly impossible to find without tearing the wiring out.

Every now and then you get lucky and find a section of the wrap of the wiring harness that has melted, which you can then tear apart and fix the offending wires.  Look for points where the harness or loom is loose and rubbing against the body of the car, and has worn through the tape and insulation.

However, since the wiring is simple on these cars, I usually rewire the whole car when I can't find the short.