Headlight short circuit

drolston

drolston

Well-known member
My '41 coupe has one of the replacement headlight switches that has a fuse holder on top. Seems like a good idea, compared to the old circuit breakers. And the old style switches were a bear to remove because of the need to insert something into an impossible-to-find slot on the switch in order to get the knob/shaft out of the switch, to get the switch out of the dash.

Anyway, the car has blown the fuse twice in the past year; once at a very dangerous time. There was no particular action associated with lights going out; just driving along, and poof! Car has a new wiring harness and I replaced taillights with LEDs. Also a new dimmer switch.

Anybody had problems with LED replacements shorting out?
How about the replacement light switch? Any problems with those?
Blew a 30 amp fuse; what does it take to kick out the original circuit breakers?
 
Well you will just have to follow along every inch of your wiring harness and check that it is not rubbed through or jammed somewhere in the chassis or under the dash. Also open up all your lights and check the bulb sockets to see if something is touching to ground. Your 30 amp fuse is pretty heavy especially if you have LEDs fitted now which dont pull much current. Fit a 10 amp fuse and turn everything ON and push and pull all your wiring around to see if you can bring the short on. Regards, Kevin.
 
I just had a situation like yours in my 41 tudor . Found the problem, the hi lo dimmer switch was occasshorting to the floor when the body frame twisted just right . I had wrapped the dimmer in rubber stretch tape and on removal had seem it had worn , allowing the low beam lead go to ground . Im 12 volt neg ground but it would not matter .
 
Ggmac said:
I just had a situation like yours in my 41 tudor . Found the problem, the hi lo dimmer switch was occasshorting to the floor when the body frame twisted just right . I had wrapped the dimmer in rubber stretch tape and on removal had seem it had worn , allowing the low beam lead go to ground . Im 12 volt neg ground but it would not matter .
Click to expand...

The dimmer switch is the leading suspect, for now. I will check it out and get back.
 
drolston said:
The dimmer switch is the leading suspect, for now. I will check it out and get back.
Click to expand...
Had similar symptoms on my 1941 and tracked it down to the dimmer switch. Seems to me like the solution is to bypass the dimmer switch. Can't say that I've ever used the dimmer switch on any car I've ever owned in four decades.


Haven't addressed how to bypass it yet, just another item on my long list. Shouldn't be too hard though. For now, if I don't use the dimmer switch, I don't blow light fuses.
 
drolston said:
My '41 coupe has one of the replacement headlight switches that has a fuse holder on top. Seems like a good idea, compared to the old circuit breakers. And the old style switches were a bear to remove because of the need to insert something into an impossible-to-find slot on the switch in order to get the knob/shaft out of the switch, to get the switch out of the dash.

Anyway, the car has blown the fuse twice in the past year; once at a very dangerous time. There was no particular action associated with lights going out; just driving along, and poof! Car has a new wiring harness and I replaced taillights with LEDs. Also a new dimmer switch.

Anybody had problems with LED replacements shorting out?
How about the replacement light switch? Any problems with those?
Blew a 30 amp fuse; what does it take to kick out the original circuit breakers?[/QUOTE

I have same problem with my '60. All the fuses are on top of the headlight switch and a bear to replace. I'm going to tap off the fuse clips on the switch and put in a remote fuse block where I can get to it.
Click to expand...
 
Well its not too hard to fit a new dimmer switch, and your car requires one to be roadworthy. In the real world (English) we call them DIPPER switch because that switch dips the headlights down, it does not dim them like in some very early cars that had a resistor in the single filament head light bulb. That switch was usually marked Bright and Dim. Regards, Kevin.
 
SoCalCoupe said:
Can't say that I've ever used the dimmer switch on any car I've ever owned in four decades.


Haven't addressed how to bypass it yet, just another item on my long list. Shouldn't be too hard though. For now, if I don't use the dimmer switch, I don't blow light fuses.
Click to expand...
No, I'm not an idiot. I'm referring to the dashboard light dimmer switch, not the headlight hi-beam/lo-beam (dimmer) switch. There's a short somewhere in the dashboard light dimmer switch that blows the tail light fuse. The tail lights and dashboard lights are on the same circuit.


If you're wired like the Ford diagrams, a short in the dashboard light dimmer shouldn't blow the headlight fuse but it's just possible (maybe not likely) that somewhere along the way the dashboard lights got wired to the headlight circuit.
 
There is a sheet metal lip on the body that allows the inner floor board to bolt to . Its raised lip is what was causing my short . It probably isn’t in as new shape and has twisted a bit in its years of service. Its interference with the low beam terminal on the dimmer switch was so slight and only when the car was parked or twisted a special way did it short , setting the breakers off .
 
Jiggled, twisted, pushed, pulled all head/tail light connections, including the dimmer switch and dash switch, and did not find a problem. I did notice that the wire bundle going to the rear from under the dimmer switch was pretty tight where it goes over the top inside edge of the frame rail. I could not get close enough to see if there was fraying, but split a length of neoprene tube and slipped it over the edge of the rail, under the wire bundle. It that was the source of occasional short circuit, it is fixed.

Intermittent electrical problems are the worst! So, I will drive during the day with headlights on for a few months to see if the short happens again, before venturing out at night.
 
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