Need help with electrical gremlin

[ragtop1968rs]

We’ll I figured out what was causing the run on problem. A few weeks ago I added a rear mounted trans cooler with a fan. That fan is the problem. I have it wired directly to the fuse box in one of the extra spots on the electric fan circuit. I’ve also tried the horn and accessories circuits. It runs on in all of them. If I unplug it, it shuts right down. How can I solve this problem without installing a manual switch for it?

[Jim Streib]

We’ll I figured out what was causing the run on problem. A few weeks ago I added a rear mounted trans cooler with a fan. That fan is the problem. I have it wired directly to the fuse box in one of the extra spots on the electric fan circuit. I’ve also tried the horn and accessories circuits. It runs on in all of them. If I unplug it, it shuts right down. How can I solve this problem without installing a manual switch for it?

What is probably happening is the fan is backfeeding into the electrical system and I can think of two ways to correct it. One is with diodes but with these they are basically one way valves and they do have a voltage drop across them to where if you have 14.4 volts going out of the wire to the fans, once it passes through the diode the voltage may be down a volt or so which means the fan spins slower than at the higher voltage.

The other way is with a relay with the main power for the relay and then to the fan now on a battery circuit and then the relay gets switched on and off by the ignition switch.

Personally, I would go with the relay design.

Jim