idiot lights

[mentalQtip]

'73 karmann ghia coupe with 1600 dual port. I was coming back from taco bell and noted that my generator idiot light didn't come on when I did my usual check. I checked the fan belt(ok) and drove the eight blocks home. I started looking for the cause and saw that I now didn't have an idiot oil light.
I tried grounding both wires and neither one causes the bulb to light. Also now I have the "B" light glowing brightly when the engine is running. Seems strange that the generator and oil idiot lights would fail at the same time and that I can't get them to light when grounded. I checked the #12 fuse and even replaced it and no change. Every other light is fine. ok, now. What happened?

Thanks

[sped372]

I don't think those lights are fused, so that wouldn't be it. Are you sure you grounded them correctly? I'm trying to remember how the housing works, I seem to recall that it's backwards from what you might think - like the housing contact is actually positive and the wire coming off the bulb terminal is ground - you may have been doing it correctly I'm just saying to make a point to double check. If it were me I'd start at square one, by pulling the bulb(s) and making sure they light with a bench supply or a spare battery. I'd hate to chase everything around if you did hit the lottery and they both burned out at the same time.

If your '73 is like our '71, take note of how tiny and temperamental the tabs on the bulb holder are (lower left of the image):


I used to have issues with the idiot lights being MIA occasionally until I spent some time cleaning that tab off with emery cloth and pried it forward a bit to give it a bit more spring contact with the speedo housing. It wouldn't hurt to make sure the metal on the housing is good and shiny too and put a dab of electrical grease there to keep it from oxidizing.

[Amskeptic]

'73 karmann ghia coupe with 1600 dual port. I was coming back from taco bell and noted that my generator idiot light didn't come on when I did my usual check. I checked the fan belt(ok) and drove the eight blocks home. I started looking for the cause and saw that I now didn't have an idiot oil light.
I tried grounding both wires and neither one causes the bulb to light. Also now I have the "B" light glowing brightly when the engine is running. Seems strange that the generator and oil idiot lights would fail at the same time and that I can't get them to light when grounded. I checked the #12 fuse and even replaced it and no change. Every other light is fine. ok, now. What happened?

Thanks

Your idiot lamps are *powered* through their shells and grounded through the center, the opposite of how most lamps work. Look at the back of the instrument cluster and you will see a black wire or two even, that plug into the "ground plate". That is actually live 12 volts coming from a fuse in the fuse box that might be blown or loose in its holder.
Colin

[mentalQtip]

Seems unlikely to me, but I replaced both bulbs and I now have lights working.