Franks73

I replaced the wire harness from the firewall forward on my 73. Should the wire that goes to the positive on the coil be part of this? The original was a resistance wire. Someone in the past ran a different wire, that runs through the fire wall next to the speedo cable. I have not been able to trace it under the dash. I would like to replace it with a new wire. Will be working with an MSD 6A, coil, distributer. Thanks for the help.

Alan 71

Hi Frank,
There are 2 harnesses in the engine compartment…. the engine harness which has 2 coil connectors as part of it, and the forward lighting harness.
Which did you replace?
Regards,
Alan

DUB

If you are going to be using a MDS system...the factory resistance wire or the wire they added may not be used and you should run your own wiring to comply with MDS' requirements to make the system operate correctly.

You will need to find the wire the previous person added and determine it if it a correct gauge size and is the way MDS wants it used to their system.

Also...Alan71 is correct...if you are looking for the resistance wire...it is NOT in the forward lamp harness.

DUB

Franks73

Hi Alan, I replaced both harnesses. There were two bundles that come out of two blocks side by side on the firewall. There is a yellow cloth wrapped wire, with a black wire that would go from the coil positive, to the starter. Those I do not need. There originally was a "resistance" wire that would be hot when you turned on the ignition key, that also went to the coil positive. That resistance wire is the one I do not see with the new harness. Also, from one of the wire bundles at the firewall is a fairly heavy gage red wire, about 15" long, with an eye connector. Pretty sure that individual wire goes to the horn relay. It is constantly hot, so trying to be careful before I make that connection. I see you often on this site, and I respect your experience, thanks for all the help you share.

Franks73

Hi DUB, thanks for responding. I replaced both harnesses, the two wire bundles that come out side by side at the firewall. The MSD diagram show a wire connection with the wire that went to the coil, that is energized when the key is on. Also one bundle has an individual red wire, about 15", fairly heavy guage, with an eye connection that is constantly hot. I think it goes to the horn relay, not 100% sure. Thanks for your help.

7T1vette

If you still run the stock points ignition system, then that wire should be a resistance type wire. Otherwise, under certain running conditions (higher rpm), there is excessive current being drawn through the points and early burning/wear-out will occur, not to mention possible coil damage.

If you have converted to an electronic ignition system, you wouldn't want the resistance wire, anyway.

Franks73

Thanks for responding. Good information. I was thinking possibly I could trace the resistance wire, and swap in a new wire for the MSD system. Nice car there Sir!