desertdatsuns.net

What is going on?
The overhead cabin light in my 260Z hasn't worked for some time. So I took it apart, cleaned everything and tested it with a a12v battery. Works fine. I used a meter to ensure the wiring had a good ground and that the power lead was reading +/-12v. But when I plug the light in it doesn't work. I then hooked up a 12v circuit tester light and it doesn't light either (yes, I tested the light first.) But with the meter I'm still seeing 12v? Any idea what's going on? Enough power for the meter but not the light? And there's no hint of light!

It is possible to get a voltage reading and have the circuit not able to handle a load. A poor connection at some point would be the likely cause. Melted fuse box contacts come to mind.

First test each side of the circuit with a test light to find out if the problem is on the ground side or hot side. Ground the test light somewhere else like the door striker. Test to battery + or fuse box to ensure light works, then test hot wire to the light. Flip to test the ground side, test from Batt + or fuse to a known good ground, then check the ground wire to the light.

Once you know which side you are missing, trace the circuit back until you find the problem.

Well, puzzle solved. It was a poor connection but not where I thought it might be. I finally found that when I tested by touching the upstream end of the fuse there was plenty of current and at the downstream end of the fuse there was plenty of current. But when I moved the probe off the end of the fuse and just touched the fuse holder, no current. Turned out there was just enough corrosion in the fuse holder to stop current flow. Needless to say I removed every fuse and cleaned each holder with a dremel and brass wire brush. File that one away under lessons learned.
That not only fixed the cabin light but the map light and one instrument light. The only devices on this circuit that still needs fixing are the door switches. The cabin light only works by its switch, not by the door switches. The "key in ignition" buzzer is on this circuit too but I removed that years ago.
On to the next challenge!