Stovebolt.com Forums The Shop Area The Electrical Bay Headlights Only With Engine Running

Hello;
Previously headlights/parking lights operated as expected; came on with ignition switch off, or on, or engine running. All stop and tail lights worked with key off as well. Recently - after months of normal operation - with key on all seemed normal. Then, in the process of foot pedal starting (key on) the fuel gauge instantly quit functioning, and the following is now the current situation:

1. headlights ONLY work with the engine running. They do not come on when ignition switch is in the OFF position. Also no headlights with ignition switch in the ON position when engine is not running.
2. parking lights DO come on when engine is off and ignition is off (i.e. they still function as normal / previous)
3. Parking lights are dimmer when engine is NOT running (I think its always been that way)
4. fuel gauge not functioning (shows Empty). I replaced the fuel sending unit last year. I just verified sending unit is not the issue. I did not change the ground and all the wires seem to be fastened properly. (no observed changes).

This is a 1951 Chevy 3600 216 converted to 12 volt alternator system last year. No electrical issues (fuses) since then.

Other electrical issues (don't know if they're connected) include;
- Dome light burns out regularly (BRIGHT when it works)
- Horn is disconnected
- Instrument panel dimmer switch does not seem to function properly.

Any thoughts or things I should look at?

Added to the mystery is this:

With the engine running and headlights on I turned the key switch to the off position and the headlights stayed on. Which is desired, but not what has been happening so I thought for some reason the problem amazingly corrected itself. However, when I turned the headlights Off, and then then turned them back ON they did NOT come back on.

I just don't understand what could have changed to make the headlights not come on when the engine is not running, and now STAY on when the engine is turned off until the headlight switch is turned off, but then will not come back on immediately (engine off) until the engine is started again.

Check to make sure that the wires on the ammeter is tight. I had a weird situation like that on my truck. I'd fire the careless guy who didn't tighten that nut, but I'm a one man show.
Check for loose connections elsewhere while you're at it.

The ammeter may be a good guess. All the things you mention attach to the ammeter, the headlight switch and/or the ignition switch. You can find the wiring diagram at: http://chevy.oldcarmanualproject.com/electrical/wiring/pdf/51truck.pdf Since it is a pdf you can rotate it and enlarge it, it is pretty easy to read.

I'm a little perplexed about the light switch behavior, but my approach would be to check the wiring according to the diagram. Assuming it worked correctly before and no rewiring was done or disturbed, it may be a non-logical cause: such as a loose connection or missing ground. Good luck.
don