1966 Mustang Coupe Wiring


New Member
Feb 13, 2020
So I’m wiring up factory style fog lights on my 1966 Mustang, and I’m at the part where I have to splice the blue/black wire of the fog light wiring harness into a power source. I’ve read that instead of splicing into the main harness, I could instead use the post at the back of the ignition switch.

I have an aftermarket radio that is also hooked up to the ignition post for the switched power for when the vehicle is running, and I’m also going to install a rally pac. I have read that I will also need to use this post for power for the rally pac.

So essentially, is the post a proper replacement power source for the lights, AND is it safe to run 3 wires off of the ignition post without blowing something?
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15 Year Member
Sep 30, 2006
Nashville TN
Factory vintage mustang wiring for lighting is...less than adequate, especially if said lighting is upgraded. First off, how do you want the fog lights to operate? On at all times ignition is on? When headlights are on only? To me, its never acceptable to run any wiring directly off the ignition switch...I will sometimes take a feed from the ignition switch to activate a relay through the 86 terminal, but the actual load will be drawn through the 87 terminal...its far better to burn out a fuse or a relay than it is to start a dash fire by overloading the poor factory wiring. Even stock the headlights work poorly because they are not run through a relay...just adding relays for headlights will vastly improve lighting.


This is how you should wire ANY high amperage accesory.