Instrument Panel Bulbs

[Dude68]

If I place a business card between the printed circuit and the case and touch a hot wire to the circuit next to warning light bulb will this test it?

[dmjlambert]

For some of the traces the negative lead of the battery is expected to be on case ground and the positive lead of the battery connected to the trace at the connector. For example, the turn signal indicators, hi beam indicator, panel lights. For others there is a fuel gauge feed trace at a particular spot at the connector that sends constant positive voltage to bulbs such as brake, temp, oil pressure. Connecting the negative lead of the battery to the traces at the connector corresponding to those bulbs will complete the circuit and test those bulbs. I'm not certain on the generator light, I don't fully understand it and others may chime in for it, but I believe it will ground one side or the other of the bulb to show over voltage or under voltage.

[68 TT]

Originally Posted by dmjlambert

... Generator light should be incandescent to have it tell you about overvoltage as well as under voltage ...

You are correct especially if you have done a CS-130 or CS-144 alternator conversion as they use the incandescent bulb resistance as the load trigger wire going to their L-terminal to make them function.