1978 electrical problem

[steve74]

I have a 1978 D-100, 6/3 sp. It gets no power to anything unless the motor is running. To start I jump posts on starter relay,it fires up everything works. Checked ignition switch, but when removed with truck running, switch will throw starter when bumped. Changed relay out also. Any ideas. Thanks

[Megunticook]

Can you explain exactly what you did with the ignition switch? I didn't follow the part about removing it "with truck running."

[steve74]

I had the column apart and removed the electrical part of the switch from its mounted position. Jumped posts on relay to start truck. Got back in truck grabbed switch and bumped to start position. With truck running it would then send juice to starter and try to engage flywheel. When truck is not running the only thing that gets power is starter relay at postive battery terminal. No headlights,nothing.But once its running, everything works,down to windshield washer. Wiring doesn,t appear to be butchered in any way. Thanks

[Delray Dude]

Sounds like the main line from your battery to the amp guage is fried or fuesable link is gone.

A quick way to remedy this is to run a decently heavy guage wire from the charging post of the alternator (the big nut on the back of the alternator) and direct to the battery positive terminal.

If that solves the problem, then it's the connection somewhere in your positive battery to the amp guage - a common problem with all older Mopars.

Personally I run a staight Charge line to the battery and use an aftermarket volt guage to monitor my charging.

Doing this will back feed the system from the alternator - which sounds like what it's doing when the truck is running as the alt is driving the power at that point.

[steve74]

Thanks that worked! Have you ever been able to track this type of problem down and fix it. I did realize that my Alt. gauge appears to be stuck about where it should when truck is running and charging right. I had already replace the fusable link in hot wire between starter relay and firewall. Wonder if problem is in wiring between firewall and gauge or just a bad gauge. Thanks again!

[Megunticook]

Glad you fixed it! If you take a peek at the firewall connector, check the fat 10 gauge red and black wires, you'll probably find a corroded connection there, maybe even some signs of overheating. Classic old Dodge issue. I removed the spade connectors on mine and ran new wire straight through the firewall to solve that.

[Delray Dude]

Thanks that worked! Have you ever been able to track this type of problem down and fix it. I did realize that my Alt. gauge appears to be stuck about where it should when truck is running and charging right. I had already replace the fusable link in hot wire between starter relay and firewall. Wonder if problem is in wiring between firewall and gauge or just a bad gauge. Thanks again!


Glad to have helped.


I suspect it'll be a bad guage (or the wiring under the dash going to it). Thats' the problem 99% of the time. If you get brave (or bored) you can pull the guage cluster, bolt the the wires that feed the guage together, (remove the charge wire you just put on) and see if it starts - if so - bad guage. But during that removal process - you might discover the problem too, a bad wire or connection.