Electric pusher fan wiring, key on & off

[JWMcCrary]

Currently in a wiring makeover and I'm wanting to have my pusher fan kick on when the temp reaches the setting but also when I stop I would like to be able to run the fan without having the key on (which is what I've been doing for years). I know this can be done with properly placed diodes using a constant 12V source and a keyed source. Do I need a diode in both 12V sources? And, what diode do I buy? part number, link, etc.

Any direction very appreciated.

 

[garberz]

My fan for my trans cooler is wired up through a three position switch.
Off
On
Auto
It runs without the key needing to be on. The auto mode uses a thermostat to turn on when the temp is reached. This is all controlled by a relay, and the relay is switched by completing the ground circuit. Simple set up. No diodes.

Mark

 

[Steve83]

Don't use diodes. Read this page & the NEXT few:

(click this text)

 

[SP73]

My fan for my trans cooler is wired up through a three position switch.
Off
On
Auto
It runs without the key needing to be on. The auto mode uses a thermostat to turn on when the temp is reached. This is all controlled by a relay, and the relay is switched by completing the ground circuit. Simple set up. No diodes.

Mark

This is the way to do it!

 

[JWMcCrary]

Yes, I agree, that is the simplest, cleanest way. I have a single throw switch that is factory labeled that I want to use. I figured it out using an extra relay and not having to buy anything else.