INSTR fuse blows when I start the engine

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golden72

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Hi everyone, I could use your expertise cause I completely suck at electrical.
I have a 1972 Dodge Dart Swinger. 318
Two problems. #1- as soon as I start the engine, the Instrument fuse (3A), I think this is fuse #7, blows. If the ignition key is turned to the ON position, all dash lights are still good. But the moment the car is started, the INSTR fuse blows, killing all dash lights.
Background: I replaced the dimmer HL switch because there were no dash lights before. Also replaced all bulb sockets and bulbs. I had the ignition switch replaced a couple of years ago. There is an orange illumination wire running part ways down the left side of the steering column. I'm not sure if I disconnected/sliced through it when removing the cluster panel but it's dangling there and I don't know where it supposed to connect under the dash.
Problem #2- The Temperature gauge isn't working.
Background: All gauges were working prior to replacing the original voltage limiter. I thought I would replaced the original one while I had the cluster out. Result: now none of the gauges worked. So, I reinstalled the original voltage limiter and now only the TEMP gauge is Not working.
I hope I've provided enough information.
Any direction on where to start is helpful.
 
golden72 said:
Hi everyone, I could use your expertise cause I completely suck at electrical.
I have a 1972 Dodge Dart Swinger. 318
Two problems. #1- as soon as I start the engine, the Instrument fuse (3A), I think this is fuse #7, blows. If the ignition key is turned to the ON position, all dash lights are still good. But the moment the car is started, the INSTR fuse blows, killing all dash lights.
Background: I replaced the dimmer HL switch because there were no dash lights before. Also replaced all bulb sockets and bulbs. I had the ignition switch replaced a couple of years ago. There is an orange illumination wire running part ways down the left side of the steering column. I'm not sure if I disconnected/sliced through it when removing the cluster panel but it's dangling there and I don't know where it supposed to connect under the dash.
Problem #2- The Temperature gauge isn't working.
Background: All gauges were working prior to replacing the original voltage limiter. I thought I would replaced the original one while I had the cluster out. Result: now none of the gauges worked. So, I reinstalled the original voltage limiter and now only the TEMP gauge is Not working.
I hope I've provided enough information.
Any direction on where to start is helpful.
Click to expand...
I also have this problem INST fuse 3A blows and I do not have dash lights. Will be watching for helpful hints. Thanks for posting.
 
Power to the gauges is keyed (part of the ignition switch). Power to the instrument lighting (orange wiring) has power at the fuse full time. The headlight switch controls that.

If you had a broken orange wire shorted to ground, it would blow the instrument lamp fuse when you turn the lights on. If you're blowing a fuse when you start the car, then theres probably a short to ground on one of the keyed circuits. Maybe even a faulty gauge is shorted to ground. You'll have to do some tracing
 
I have an idea 'cause I've seen it, but can't explain it very well.
Typical OEM ignition switch had 4 wires coming down to a connector with 5 ports. The orange wire for lighting came down separately and was poked into that 5th port. About 5 years ago a bunch of aftermarket switches appeared at part stores with 5 wires. YEP, a big *** black wire for who knows what, from the switch to that 5th port. Nowhere left to poke the orange wire. Install it as received and that extra switched wire would connect to the cars harness illumination wire. It would toss a big voltage in the wrong direction and blow that fuse the instant the switch went to start position.
If you determine this is the case, what to do? Best to just leave that extra big black wire where it is so it's safe. Back the other wire out of the cars harness connector and make it to the orange wire outside/beside the original connector(s). Done
 
70Duster440 said:
Power to the gauges is keyed (part of the ignition switch). Power to the instrument lighting (orange wiring) has power at the fuse full time. The headlight switch controls that.

If you had a broken orange wire shorted to ground, it would blow the instrument lamp fuse when you turn the lights on. If you're blowing a fuse when you start the car, then theres probably a short to ground on one of the keyed circuits. Maybe even a faulty gauge is shorted to ground. You'll have to do some tracing
Click to expand...
Makes sense. I will inspect further. Thanks.
 
70Duster440 said:
Power to the gauges is keyed (part of the ignition switch). Power to the instrument lighting (orange wiring) has power at the fuse full time. The headlight switch controls that.

If you had a broken orange wire shorted to ground, it would blow the instrument lamp fuse when you turn the lights on. If you're blowing a fuse when you start the car, then theres probably a short to ground on one of the keyed circuits. Maybe even a faulty gauge is shorted to ground. You'll have to do some tracing
Click to expand...
 
RedFish said:
I have an idea 'cause I've seen it, but can't explain it very well.
Typical OEM ignition switch had 4 wires coming down to a connector with 5 ports. The orange wire for lighting came down separately and was poked into that 5th port. About 5 years ago a bunch of aftermarket switches appeared at part stores with 5 wires. YEP, a big *** black wire for who knows what, from the switch to that 5th port. Nowhere left to poke the orange wire. Install it as received and that extra switched wire would connect to the cars harness illumination wire. It would toss a big voltage in the wrong direction and blow that fuse the instant the switch went to start position.
If you determine this is the case, what to do? Best to just leave that extra big black wire where it is so it's safe. Back the other wire out of the cars harness connector and make it to the orange wire outside/beside the original connector(s). Done
Click to expand...
I hadn't considered that there might be a difference between the original and aftermarket connectors. I will compare it with the service manual diagram.
 
golden72 said:
I hadn't considered that there might be a difference between the original and aftermarket connectors. I will compare it with the service manual diagram.
Click to expand...
Easiest way to rule my experience out... Disconnect the aftermarket replacement ignition switch, replace the blown fuse, and pull the lights on. If everythings good except the column mounted shift indicator, there's your sign.
At that point you would use a test lamp to determine which wire in the cars harness connector is hot only when lights on. That's the one that the orange wire connects to.
Good luck
 
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Do you have an electric choke on an aftermarket carb? Try unpluging it and see if the fuse still burns out. I've seen where people tie into where ever they find juice with 'key on' and connect to the choke. Then, some time later when the choke's heating element goes to ground it takes out the fuse. This happened to me.
 
RedFish said:
Easiest way to rule my experience out... Disconnect the aftermarket replacement ignition switch, replace the blown fuse, and pull the lights on. If everythings good except the column mounted shift indicator, there's your sign.
At that point you would use a test lamp to determine which wire in the cars harness connector is hot only when lights on. That's the one that the orange wire connects to.
Good luck
Click to expand...
That's an excellent idea. I usually get over to the folks place once a week at the end of the week to work on it. I will post an update complete all the necessary steps and resolve the problem. Thank you.
 
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