Short on Circuit 7 (not six) - 1974 Plymouth Valiant Scamp

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DigitalRelay

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The car I recently bought, got running and drove around the block had a blown fuse in circuit 7 (not six) when I bought the car. I started digging in today with my mymopar wiring diagram. I found one of the wires from the trunk light switch seemed to be rubbing on sheetmetal and I suspected was shorting, so I disconnected that connector and put a new fuse in. It did not blow immediately, and I noticed the flashers inside the car seemed to be flashing, but only the left arrow inside was illuminated, and several lamps are either missing or burned out. But by the time I could start looking at those, I heard the ignition buzzer start buzzing and a few seconds later, the fuse burned out again.

I'll start tracing things through the ignition switch next. I've already seen some suspect splices under the dash from a previous owner, but I thought I'd ask here in case there are any common known issues I should track down first.

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Can be a million things at least you got a good idea on which circuit to look at.
 
Here's a list of what's on fuse 6.
Ignition run feed
Voltage limiter
Fuel gauge
Low oil indicator lamp
Brake warning indicator light
Heated rear window relay
Interlock control unit
On the 74 model exam where the ignition switch connector mates with dash harness. Burn marks are often found in this area.
 
townsend said:
Here's a list of what's on fuse 6.
Ignition run feed
Voltage limiter
Fuel gauge
Low oil indicator lamp
Brake warning indicator light
Heated rear window relay
Interlock control unit
On the 74 model exam where the ignition switch connector mates with dash harness. Burn marks are often found in this area.
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This is awesome, thank you so much!
 
Is it possible you mean circuit #7? In your photo, you have fuse 7 empty. Fuse #6 in that photo is the first one top left, and is fused for 3 amps.

The items you mentioned... trunk light, buzzer, E-Flashers... are non-switched items. The items Townsend quoted you from the book are all switch fed. Plus, you said you drove the car. If the run ignition run circuit in included for fuse 6, seems that fuse 6 would need to be in good order for the engine to run.
 
Charlie71 said:
Is it possible you mean circuit #7? In your photo, you have fuse 7 empty. Fuse #6 in that photo is the first one top left, and is fused for 3 amps.

The items you mentioned... trunk light, buzzer, E-Flashers... are non-switched items. The items Townsend quoted you from the book are all switch fed. Plus, you said you drove the car. If the run ignition run circuit in included for fuse 6, seems that fuse 6 would need to be in good order for the engine to run.
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You are correct. I was mistaken. It's circuit 7 that's been the issue. I'll edit that post. Thank you!
 
I would start with disconnecting everything in that circuit... put in a fresh fuse and then go back and reconnecting things. This will not identify a problem with wiring leading to the item. It will only identify a problem with the item itself. Look inside bulb sockets such as the trunk light. Those sockets with springs in there sometimes get kinda jacked up over the years. Springs fall out of position... that little fiberboard with the contacts breaks and causes contacts to contact each other.

You mentioned repairs from a previous owner.... man, that's bad ju-ju! Double check his work! I had a 67 Galaxie fastback that kept blowing fuses for the dash lights. Put in a fuse, pull out the light switch, and POOF! Every time. Turned out, there was an unused light lead under the dash that the previous owner musta thought was a ground because there was no voltage on it (unless you turned on the lights). He wired that lead directly to the ground of an under-dash stereo he had installed. The stereo worked fine since it was bolted to the metal dash... so it was grounded. Unfortunately, so was that light lead and after I disconnected it, my dash lights stopped blowing fuses!
 
Fuse 7.
Ignition switch lamp time delay relay
Ignition switch lamp
Cigarette lighter
Seat belt - key in - buzzer
Seat belt lamp
Hazard flasher circuit
Stop lamps
Dome lamps
Map lamp
Glove box lamp
Trunk lamp
 
Well there's nothing absolutely suspicious looking about that mess! :lol:

Do you suspect that was taken apart previously? I bet whoever did that was probably chasing blown fuses for some time and never thought to look in there!
 
Charlie71 said:
Well there's nothing absolutely suspicious looking about that mess! :lol:

Do you suspect that was taken apart previously? I bet whoever did that was probably chasing blown fuses for some time and never thought to look in there!
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There’s some other butchery nearby, so yes, I think someone was in there and didn’t mind the wiring on install. I’ll get it all sorted eventually!
 
I would also pull out the rear seat and inspect the rear harness. The trunk lite circuit, for sure

You can eliminate the hazard flashers by simply unplugging the flasher. Make sure you get that and not the turn flasher

Certainly possible, the dome lamps.

If this gets difficult, investigate one of the flashing circuit breaker test rigs. These are a light duty breaker that you stick into the fuse holder. The short causes the breaker to cycle. The short generates a magnetic field in the harness, and the kit comes with a magnetic meter which you run along the harness to detect a change in the current

Just for reference, there are others, and cheaper copies

22988285_kdt_kdt2524_pri_larg.jpg

Another thing you can do, is to "rig" an old stop/ tail socket with an 1157 and wire it to the fuse holder. Wire the socket shell to one clip, twist the two socket wires together and wire them to the other fuse clip. The light will show when there is a load on the circuit, and show brightly when there is a short. The lamp will prevent any damage to any of the wiring in that circuit.
 
67Dart273 said:
I would also pull out the rear seat and inspect the rear harness. The trunk lite circuit, for sure

You can eliminate the hazard flashers by simply unplugging the flasher. Make sure you get that and not the turn flasher

Certainly possible, the dome lamps.

If this gets difficult, investigate one of the flashing circuit breaker test rigs. These are a light duty breaker that you stick into the fuse holder. The short causes the breaker to cycle. The short generates a magnetic field in the harness, and the kit comes with a magnetic meter which you run along the harness to detect a change in the current

Just for reference, there are others, and cheaper copies
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22988285_kdt_kdt2524_pri_larg.jpg

Another thing you can do, is to "rig" an old stop/ tail socket with an 1157 and wire it to the fuse holder. Wire the socket shell to one clip, twist the two socket wires together and wire them to the other fuse clip. The light will show when there is a load on the circuit, and show brightly when there is a short. The lamp will prevent any damage to any of the wiring in that circuit.
Click to expand...
I'll have to grab a socket on my next scrap yard run. That sounds like something that will come in handy for years.
 
Very much. If you get something like a major short, you can wire a lamp in series with the main battery ground. Steve up there in Canada will tell you, he once had a shorted alternator.
 
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