Triumph Repair: Turn Signal etc, turn signals, electrical problem

Question
My 1979 spit has one of those magical electrical problems.  Most of the interior meters and signals do not work "sometimes" and then come on when they feel like it.  It does not seem to be loose wiring since I check it all and it is not related to bumps.  The turn signals do not work when the tachometer does not work.  Some times when I turn the turn signal on, it shuts down the signals and the tach.

Any ideas where to look?  Headlights always work no matter what

Answer
Hi Tim,

I found that while working in dealerships on electrical problem that You need to forget symptoms as they only tell you something is wrong. The ONLY way to correct an electrical problem is by testing. And the testing must be done while in the failed mode. (something not working)

Also, when several items fail you MUST pick only one of the items to test. By looking at your wiring diagram pick the simplest circuit that has failed. I found it best to start at the "Load" (the item that has failed) First with a 12v test light confirm that there is no power at the item, then power your test light and confirm that the item has a good ground. Then use your diagram to go to the next joint in the circuit toward the source (power supply) On some simple circuits you can go to the half way point in the circuit and test for power thus dividing the circuit in half.

If you find power at the half way point you can then divide that half into half again on the diagram. This is called "Bracketing". It is faster then going one joint at a time.

Most of the time when you have several items that have failed at once you will correct all of them when tracing down only one circuit.

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

Howard