Triumph Repair: lamp wiring, triumph spitfire, high beams

Question
QUESTION: Hi Howard,
I'm putting together a body off restoration and am using the original wiring harness, on which I performed a quick repair on a connection, everything else seemed to be in order.  The plan is to test everything and troubleshoot any issues before putting the carpets and seats in, and am running into trouble in a few areas.  Headlights (low), tail lights, parking lights, brake lights, and dashboard lighting is all functioning well, but testing of high beams, hazards, and reverse lights has failed.  Wondering if you can point me in a direction, if they all have some sort of common point to check.  I've cleaned the terminals on the back of the hazard switch which I've read is a common problem.  Any other ideas you have would be helpful.
Thanks, as always, for your time here.
Regards,
Eric

ANSWER: Hi Eric,

I may be able to help but you need to tell me what kind of car you have.

Howard

---------- FOLLOW-UP ----------

QUESTION: Hi Howard, haha, sorry.  1974 Triumph Spitfire.
Thanks again,
Eric

Answer
Eric,

I learned when working in MG, Triumph and Jaguar dealerships that any time you have several electrical circuits that have failed, you must pick only one of the circuits to work on. Most of the time when you find the problem with that one circuit, it will correct the others.

I found it to be a waste of time trying to figure out what was wrong by symptoms. Testing is the only sure method to correct an electrical problem.

The minimum tools necessary to do the tests is a wiring diagram of the car and a 12v test light or voltmeter.

I always try to pick the easiest circuit to test. In your case I would use the high beam circuit to trace. I always like to start at the "Load" (high beams in your case) and test toward the "Source" (battery).

Your tests will be easy as you know already that you have power from the head light switch to the dimmer switch (blue wire). So your first test need not go to the load (head light high beam) just test the output from the dimmer switch on the column. Turn on the head lights and put it on low beam and confirm that you have low beams on and that there is power to the blue w/red tracer wire out of the dimmer switch. If that is correct now flip on high beams and look for the high beam indicator light on the instrument panel. Then test with your test light the Blue w/White tracer wire at the dimmer switch. That is the wire that powers high beams.

Your other electrical problems are not related to the high beams so you may have several problem, possible wires plugged into wrong places.

For example test the tail lights at the master head light switch. The "Load" (tail lights) is the Red w/green tracer wire on the head light switch so turn the head lights on and test that wire for power. If you have power go to the fuse box and test the Red w/Green tracer wire at the fuse for power and across the fuse to the Red wires coming out of the fuse box.

You can run the same kind of test at the fuse box for the other lights that are out. Turn the ignition switch on and test the White wire at the fuse panel for power and across the fuse to all the green wires to see that the reverse lamps are receiving power.

If you don't have a diagram of your car let me know and I will post one on my web site for you to copy.

Howard