I have a shutoff switch in my rear bumper because I have a trunk mounted battery. I used a Painless Wiring Relay Kit to make the shutoff ACTUALLY shut the car down without feedback from the alternator keeping the car running.

Over the last few months I have been watching my volts going down as the vehicle got warmer down to barely 12 volts with about a 40 amp load. tested the alternator (104 amps), and the battery brand new and perfect.

Turns out I have a 1.5 voltage drop over the shutoff relay which is connected directly to my alternator..I have bypassed it for now and running at 13.6 with a full load on the system...

Has this happened to anyone too? and any suggestions for wiring the turn off switch differently?

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'71 468 Street/Strip Monte Carlo 3950lbs, 9.8:1, 3.55's, 11.46 @ 117, 7.29 1/8 mile
1.62 60'

Well, I've never done this but it sounds like the contacts in your relay have been damaged. This site talks about using a remote starter relay. Maybe a Ford solenoid would work. Best I can think of. http://www.classictruckshop.com/one_wire.asp

Hey Tom, I am using a remote starter solenoid. I have the GND wire from my cuttoff switch going to the ground terminal in one of the 3 relays in the front of the car that runs everything. Once this relay is flipped, everything cuts out, alternator, fans, ignition et cetera.
Switch works great with no problems, and I really like the remote solenoid set up. Keeps the starter and the wiring in general clean.

thanks, I use chrysler starter relays for fans and neutral safety switch and a Ford Solenoid for my starter. will wire up the Ford for my cutoff too.

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'71 468 Street/Strip Monte Carlo 3950lbs, 9.8:1, 3.55's, 11.46 @ 117, 7.29 1/8 mile
1.62 60'