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Short in lighting circuit
#1399363 Sun Feb 28 2021 09:43 PM
Joined: Jan 2019
Posts: 95
C
'Bolter
while driving my 54 3100, with 235 engine in the dark. Lights went off. a few seconds they came back on. this happened until i got home. reading the manual it says there is an interupter in the head light switch that would cause this if there is a short which caused a current draw over 42 amps. I replaced the switch while working on the truck. This was the first time i have driven it at night. Does anyone have any suggestions for finding the short. i drove the truck in the daylight with my bright lights on and saw the interruption in the bright light indicator light on the dash. Alny help would be appreciated. it started after driving for a few miles with the lights on.
Thanks

Re: Short in lighting circuit
clrh2ofrank #1399369 Sun Feb 28 2021 10:15 PM
Joined: Dec 2008
Posts: 1,006
5
'Bolter
Could be a bad ground on the headlights, or bad connections on the hot wires to the head lights causing high resistance.


Brian
1955.2 3100 Truck


The older I get the more dangerous I am!!!!!
Re: Short in lighting circuit
clrh2ofrank #1399371 Sun Feb 28 2021 10:25 PM
Joined: Mar 2019
Posts: 1,232
G
'Bolter
Check da connection at da dimmer switch. Know issue area.

Re: Short in lighting circuit
clrh2ofrank #1399374 Sun Feb 28 2021 10:43 PM
Joined: Sep 2011
Posts: 855
B
'Bolter
Originally Posted by clrh2ofrank
I replaced the switch while working on the truck.
Thanks

So the switch was replaced during rehab, not failure?
Is the rig 6 volt?


BC
1960 Chevy C10 driver 235 T5 3.73 dana 44
1949 GMC 250 project in waiting
1960 C60 pasture art
G.M dealer tech since 1980 & counting
Re: Short in lighting circuit
clrh2ofrank #1399376 Sun Feb 28 2021 10:49 PM
Joined: Jan 2019
Posts: 95
C
'Bolter
Thanks to 55 Shaker and to Glenn's towing. Do you think the interrupter could be reating the intermittent outage?

Re: Short in lighting circuit
clrh2ofrank #1399431 Mon Mar 01 2021 02:37 AM
Joined: Feb 2004
Posts: 22,144
H
'Bolter
A light switch has a bimetal strip that acts as a self-resetting circuit breaker so you don't lose the lights entirely like would happen with a blown fuse. The dimmer switch is a good place to start looking for a problem. It lives in a very bad environment- - - -lots of road splash, salt, etc. It can develop a short that will cause the breaker to cycle. Try disconnecting the wires at the headlights one at a time to see if the problem goes away. If not, keep backing up along the wiring, from headlights, to the dimmer switch, to the headlight switch, disconnecting wires until the circuit breaker stops cycling the circuit on and off.

Did you happen to install brighter headlights recently, like halogens or LED's? Some of those types of lights draw enough current to need relays in the circuit to prevent overloading the breaker in the headlight switch.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Short in lighting circuit
clrh2ofrank #1399438 Mon Mar 01 2021 03:51 AM
Joined: Apr 2007
Posts: 850
L
'Bolter
Another suggestion is that it could be a dirty connection causing resistance at the bimetallic strip that Hotrod Lincoln references. This happened to me and there was no short, just needed to clean the points at the connection. What happens is that the dirty connection gets hot with a normal current draw, as you would have with the headlights on, and the heat causes the bimetallic strip to open the circuit. After 5 minutes, things cool down, lights come back on, only to repeat every few minutes.
Kent


1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix
Re: Short in lighting circuit
clrh2ofrank #1399445 Mon Mar 01 2021 04:24 AM
Joined: Jul 2000
Posts: 1,177
G
Shop Clutterist
First thing I would do is a thorough inspection of the wiring. Follow the wires from the headlights back to the switch. Look for places where the wires could be grounded by chafing against metal. Look for areas where wires could have had the insulation burnt off by hot parts such as the exhaust. Look for wires spliced together and wrapped up in tape (possibly highlight pigtails); a good place for short circuits.

Reread Hotrod Lincoln's post about disconnecting the wires at the headlights and working back to the switch.


Gord
----
1954 1/2 ton 235 4 speed
Re: Short in lighting circuit
Hotrod Lincoln #1399526 Mon Mar 01 2021 05:25 PM
Joined: Jan 2019
Posts: 95
C
'Bolter
Does anyone know if the new headlight switches have the thermalcircuit breaker in them? The supplier who i bought it from acted like he never heard of it. I had seen it discussed in the 1954 Chevrolet Shop manual, page 12-37. my problem sounded like exactly what would happen. I'm not sure how long it takes for the breaker to cool so light would come back on. mine were only a few seconds to a minute. Scarry driving when it was a minute.
Thanks for all the suggestions.

Re: Short in lighting circuit
clrh2ofrank #1399539 Mon Mar 01 2021 06:07 PM
Joined: Mar 2010
Posts: 301
B
Curmudgeon
This one does (attached pic). It's from Classic Parts.

99% out of a 100% of the time, the problem is in the dimmer switch.

If you truly have a short, your are risking a fire or frying your wiring.
You need to nail this problem ASAP.

1. Remove both head lamp sealed beam bulbs
2. Remove dome light bulb
3. Remove fuses (firewall box) for tail and stop lights.
4. Connect voltmeter across battery
5. Engine not running or cranking

You are looking for a significant voltage drop when you pull the knob on the headlight switch.
Watch your dash ammeter gauge for a significant deflection.
If your current or voltage has a significant change then you may have a problem somewhere else.
Report what you see.

Attached Files
HL Switch.jpg (38.9 KB, 93 downloads)
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