1973 Road Runner Dash Wiring Issue

I am getting close to finishing up the complete restoration of my '73 Road Runner. All of the wiring harnesses were replaced with brand new M&H harnesses where available, and unavailable harnesses were reconstructed with new wires to the same specs as OEM or better. I triple checked everything and had all connectors labeled for proper placement when installed. The only changes were bypassing of the AMP gauge and conversion to a Volt gauge ( MAD Electrical). All of the relays and switches were replaced with new or NOS. I also converted to LED panel lamps to reduce the electrical draw on the system. I installed the dash harness in the dash before installation into the car to ensure everything was connected right. Bottom line, I did everything I could to ensure I didn't have any wiring issues.

Last week when I finally turned the key to start the car and test out the electrical system, I had no panel lights and the 5A fuse (the only 5A fuse in the bulkhead, top right cavity) blew almost instantly. I replaced the fuse and had the same result. I also had a smell of hot wires and light smoke start to come from an unknown source behind the gauge cluster. The headlights and front marker lights worked fine (rear lights are not installed yet), the brake light on the dash worked, the manual reverse light worked, the horn worked, and the ignition worked to activate the starter. I removed the dash and inspected the wiring harness, but could not locate any source of the hot wires or see anything pinched or damaged.

Thinking that it was possibly a bad chassis ground, I spent today running a 10 Gauge wire from the ground wire on the radiator support directly to where I have everything grounded behind the dash. When I tried everything today, I had the same results except the headlights didn't work. When I would attempt to put the 5A fuse into the bulkhead, it would blow before I could even get it snapped in place. I tried to bypass the fuse to see what would happen and I had smoke and a hot smell coming from the area of the headlight switch connector almost immediately.

Where do I go from here and what can I try to get things working? I have yet to see the panel lights work and now the headlights aren't working either. The headlight switch is brand new and I didn't do anything to modify the plug or connector for the headlight switch on the new harness.

Sorry for the long post, thanks for any suggestions or help.

Disconnect the head light switch and figure out what system the fuse that is blowing covers and start looking at that first, it wouldn't be the first time a brand new part was bad.Let us know what you find.

Not from an inadequate ground, there is a dead short up in there. No choice but to open things up & see what is grounded that ain't supposed to be. I would keep a batt cable disconnected. Your ohmmeter is your friend right now. find the smoked circuit & trace it. EDIT pull the headlight sw & ohm each cavity to ground & find which one has zero ohms (dead short) & work that circuit downstream toward the dash panel.

For what it's worth, the FSM shows the 5A fuse cavity controlling the panel lights, which kind of makes sense since those aren't working. I am really dreading trying to troubleshoot things now that the dash is in the car, as there is little to no room to really get up behind the dash to start checking things. Thanks for all of the suggestions so far, at least I have an idea what I can try to look at next.

likely it will be fine if you dont bypass the fuse. When the time comes I'd drop the column a bit/protect it with a rag & pull the dash (as needed for your vehicle). I'm trying to think WHERE it might be grounding out/dead sorted

Purchased this to troubleshoot a confounding brake light short in my 71 Vette. Have used a couple other times on issues with other cars.

Handy, albeit expensive tool. May help.

http://www.amazon.com/Electronic-Specialties-230-Audible-Trouble/dp/B008LQ61JE/ref=cm_rdp_product

Also you can buy circuit breakers that fit into glass fuse clips in your fuse block,,,may not be useful to your problem,,,just letting you know. Not sure if come in 5 amp size however.

Did you bench test complete dash wiring assembly before installing in car,,,not certain that I understand that you did so.

As an aside, recently purchased MH dash wiring for my 70 Challenger. Yet to install.