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| | | | Joined: Aug 2017 Posts: 15 New Guy | | New Guy Joined: Aug 2017 Posts: 15 | I'm working on my 1950 GMC FC152 with the original 6V positive ground system. I had just about everything working perfectly in the electrical system, and the truck is a solid, reliable runner. Then last night I go to test the new instrument panel bulbs I had installed with the engine running, and it shut off immediately. Tried the same thing again with the same result. Talked to a guy at Fillingstation, and he suggested it is something wrong with the light switch. Any thoughts? I'm at a loss.
1950 GMC 150
| | | | | Joined: Sep 2001 Posts: 29,269 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,269 | The light switch is a good guess - it has built-in circuit breakers. You might want to check the wiring connections to the light switch. Do you have a GMC Maintenance Manual - check the electrical section? Here is Chev truck wiring - your GMC's could/should be the same. | | | | | Joined: Aug 2017 Posts: 15 New Guy | | New Guy Joined: Aug 2017 Posts: 15 | Is there any way to repair or reset those circuit breakers?
1950 GMC 150
| | | | | Joined: Jul 2000 Posts: 2,187 Insomniac | | Insomniac Joined: Jul 2000 Posts: 2,187 | Lighting and ignition are two separate circuits - at least they should be if the wiring is correct.
You need to do some testing before you decide on the solution. Turn ignition on. What is the voltage at the distributor? Now turn on the lights. What is the voltage at the distributor now?
Gord 🇨🇦
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1954 1/2 ton 235 4 speed
| | | | | Joined: Feb 2004 Posts: 29,742 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,742 | Do the lights work with the engine stopped? It sounds like you've got a short somewhere in the lighting system that kills enough voltage when the light switch is turned on to starve the coil for current. I'd suspect the dimmer switch.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Mar 2010 Posts: 10,270 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,270 | I had a similar issue as yours and it turned out that the current owner did not tighten the nut which holds the wire to the ammeter. It was just laying there conducting some electricity most of the time. I guess over time, the terminal began to accumulate some tarnish and maybe some soot from arcing to the point that it stopped conducting electricity consistently.
BTW, that "current owner" is still in place. His wife considers him quite the catch despite his occasional mechanical ineptitude.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
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