Stop lights blowing fuse

XPlorID

XPlorID

Member
Feb 9, 2012
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Using the brakes is blowing the stop/dir/hazard 20 amp fuse. Trying to narrow the problem area (and using lots of fuses) the directionals and hazards
work fine and activate the lights as they are supposed to. Guessing that the wiring to the rear lights is common to the dir/haz/brakes, does that
eliminate the wiring going to the rear as the problem?

I just swapped the stop light switch and it made no difference. Push the brake pedal and the fuse will blow after a few seconds - I do not know if
the brake lights are activated when this happens. The problem appeared suddenly, worked fine prior.

I am a fairly lame mechanic but especially crippled with electrical stuff. I have a multimeter and almost know how to use it.

Jeff
--
1973/94 GMCII Manny 6.5 TD AL radiator 1 ton front 4 bags back, Huber TBs
 
Instead of blowing fuses, there is a way to use a light bulb and alligator clips.
Hopefully someone can explain how to.
 
Look to see if you have a trailer harness. If you do, they are subject to
chafing as they dangle beneath the rear of the coach, and OFTEN are wired
by unskilled technicians who leave wires stripped back too far. Look in the
drivers side access panel in the rear of the coach.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

> Instead of blowing fuses, there is a way to use a light bulb and alligator
> clips.
> Hopefully someone can explain how to.
>
>
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Hi Jim - no trailer harness on this coach.
--
1973/94 GMCII Manny 6.5 TD AL radiator 1 ton front 4 bags back, Huber TBs
 
The trailer harness was installed by GM and is often out of sight tucked up into the metal channel above the bumper.

Emery Stora
77 Kingsley
Frederick, CO

>
> Hi Jim - no trailer harness on this coach.
> --
> 1973/94 GMCII Manny 6.5 TD AL radiator 1 ton front 4 bags back, Huber TBs
>
>
>
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> Hi Jim - no trailer harness on this coach.

Lets try and eliminate the wiring going to the back.
Locate the 10 wire connector between the instrument panel harness and the side body harness (it should be on the left side upper dash and disconnect
it)
That should eliminate the wiring to the rear.

If you cannot find that one there is a 6 wire plug that connects the side body harness to the rear body harness and it says it is in the rear of the
coach

If the fuse does not blow then the problem is back there.

If the fuse still blows find the 11 wire plug near the bottom the steering column and unplug it. If the fuse does still blow look at the flasher if it
does not blow it is either the wires to the hazard switch or turn switch or one of those switches.

--
Tom Lins
Elkton, FL
77 GM Rear Twin
 
Thanks Tom that sounds like a plan. I have looked for a trailer harness in the past and never found one. This is a GMCII by Explorer, body off in
1994, and about every original circuit has been invaded or hacked, so I can never tell.

I'll let you know what I find, thanks for the guidance.

Sunny and in the 50s in Boise today, another day or two of that and I might get this fixed.
--
1973/94 GMCII Manny 6.5 TD AL radiator 1 ton front 4 bags back, Huber TBs
 
I assume that you have removed BOTH bulbs from the rear lights and tried to see if it blows fuses that way.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Hi Ken - that was kind of my original question - if the flashers and directionals work as they should and do not blow the fuse, does that mean the
problem is forward and not aft. All 3 functions use the same wiring and bulbs to the rear of the coach, right?
--
1973/94 GMCII Manny 6.5 TD AL radiator 1 ton front 4 bags back, Huber TBs
 
You could have a bulb with a compromised filament. This can draw more current. Try easy stuff first and you can inspect sockets while changing lamps.

--
John Lebetski
Woodstock, IL
77 Eleganza II
 
John, also check the wiring around the vicinity of the dimmer switch on the
floor next to your left foot. Lastly, if you have mice, all easy solutions
are off the table.
Jim Hupy

> You could have a bulb with a compromised filament. This can draw more
> current. Try easy stuff first and you can inspect sockets while changing
> lamps.
>
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
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> Unsubscribe or Change List Options:
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>
 
> Hi Ken - that was kind of my original question - if the flashers and directionals work as they should and do not blow the fuse, does that mean
> the problem is forward and not aft. All 3 functions use the same wiring and bulbs to the rear of the coach, right?

You are correct. I need to go look at the wiring diagram to refresh my memory. I believe that the brake switch feeds the turn signal and 4 way
flasher assembly on the steering column and then the wiring goes to the rear lights of the coach. So you are probably correct that the rear bulbs are
not shorted. But... shorted bulbs and sockets are very common, so I might take them apart anyway just to make sure. I am wondering if there is
something else besides the brake lights drawing power off of the brake switch.

There is a kill circuit for the cruise control also on that switch and it is wired to the brake lights. You might want to find that cruise control
circuit and disconnect it. This might just be a bad / shorted brake light switch. I need to go look at the wiring diagram before I say too much more
from memory and find out later that I am wrong.



--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
I don't think you have eliminated the wiring to the read necessarily. I suspect since you say it takes a bit before the fuse blows you haven't a
complete short. I'd look for a damaged wire, corroded switch or socket. One wire at a time...

--johnny

--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
 
The culprit appears to be the rear passenger side socket, right on johnny.

The hazard/directionals were not working properly as thought, just taking longer to blow because the power to stop light is not constant I guess.
Following the circuit dark green (RH rear) wire found resistance in the contact at the socket. Cleaning did not help, needs to be replaced I guess.

Thanks for all the help and guidance, now to find a replacement socket. These are the somewhat modernized tail lamp lenses from the early 90s, not
sure of the sockets are the same.

Jeff
--
1973/94 GMCII Manny 6.5 TD AL radiator 1 ton front 4 bags back, Huber TBs
 
high resistance will not cause the fuse to blow low resistance to frame will remove all the lamps to the brake lights and disconnect the switch at the
brake pedal using your multimeter you should have a high resistance between the white wire at the brake switch and the frame of the coach if not then
you need to try and find where the short is . as they say divide and conquer
--
Trevor
Brisbane Australia
Siesta Koala 76 Edgemont (old Bobby Moores)
71 Cadillac Eldo Convert
58 Cadillac Eldorado Brougham Project
 
Thanks mate, and sorry, should not have used the word "resistance", I do not know what I am talking about technically.

I pulled the dark green directional wire (RH rear) from the turn signal switch plug at the bottom of the column
Ran a long "jumper" wire from that pulled (turn signal switch) wire to the RH rear socket contact and got a very weak turn signal light, trying
several spots on the contact.
Pulled that side of the contact out of the RH rear socket and the jumper wire operated the turn signal light correctly when connected directly to the
bulb.
Cleaned the socket as best I could, put it back in the socket and tested again with the same results. Did that 3 times, thinking I had found the bad
spot in the circuit.

Hope that makes sense, no knowledge but a little logic.

To be safe, I left the dark green directional wire disconnected at the plug at the column, now everything works except the RH rear stop
light/directional light, and the fuse does not blow.

At least for the moment I can move the coach with a single (LH side) brake light functioning and 3 out of 4 directionals.

That's as close as I am going to get today, not sure what I am missing yet.

Jeff
--
1973/94 GMCII Manny 6.5 TD AL radiator 1 ton front 4 bags back, Huber TBs
 
if it is not blowing fuses now it sounds like you may have a short in the dark green wire to the RH stop. as for the dim lamp when in the socket make
sure you have a good ground on theblack wire this should be close to zero ohms to the frame
--
Trevor
Brisbane Australia
Siesta Koala 76 Edgemont (old Bobby Moores)
71 Cadillac Eldo Convert
58 Cadillac Eldorado Brougham Project
 
> Thanks mate, and sorry, should not have used the word "resistance", I do not know what I am talking about technically.
>
> I pulled the dark green directional wire (RH rear) from the turn signal switch plug at the bottom of the column
> Ran a long "jumper" wire from that pulled (turn signal switch) wire to the RH rear socket contact and got a very weak turn signal light, trying
> several spots on the contact.
> Pulled that side of the contact out of the RH rear socket and the jumper wire operated the turn signal light correctly when connected directly to
> the bulb.
> Cleaned the socket as best I could, put it back in the socket and tested again with the same results. Did that 3 times, thinking I had found the
> bad spot in the circuit.
>
> Hope that makes sense, no knowledge but a little logic.
>
> To be safe, I left the dark green directional wire disconnected at the plug at the column, now everything works except the RH rear stop
> light/directional light, and the fuse does not blow.
>
> At least for the moment I can move the coach with a single (LH side) brake light functioning and 3 out of 4 directionals.
>
> That's as close as I am going to get today, not sure what I am missing yet.
>
> Jeff

Jeff,

I am straining at some very old neurons here, but GM went though several versions of sockets for brake/tail light assemblies. I had some trouble with
most. The two I remember best are:
One that had the two contacts though a piece of phenolic. That contact was crimped onto the wire and the contacts and all were loaded into the socket
with a spring. With time and age, the phenolic would let the back side of the contact down so it could short to the spring. The spring was not a
real hard short, but the current would soften it. And a guy without a lot of patience would end up throwing things because you could pull the bulb
out and clean thing and it would work until it didn't again.
The other was a trip too. They had a rubber plug with the contacts in it. This is no better. The rubber goes bad with age and will create a very
reliable intermittent short in the light circuit. You will never find it unless you pull the whole assembly apart.

Now, What to do if this sounds like your case.
Go to a local store front autoparts store and look for the wall of electrical stuff. Someplace will be a double contact socket with two wires. These
come in both the king that fit in a big hole and the kind that are just a socket. Buy all you find that you think have a chance and save the receipt
so you can take the others back. It may take some ingenuity to make this repair, but I have done it.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
Thanks Matt - the rear lights and sockets appear to be listed as 1985 Chevy G20 Van at Auto zone as Part Number: 85832 (Dorman) $6.49 - it's a 3 wire
socket

Trevor - the "short" is somewhere from the connector going to the rear (under dash on left drivers side) and the bulb, I thought my jumper antics
identified the socket itself, maybe not.

For $6.49 I am going to find out tomorrow.

--
1973/94 GMCII Manny 6.5 TD AL radiator 1 ton front 4 bags back, Huber TBs
 
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