Yes, the LEDs will work that way. I actually have the LEDs, but no switch.

 

So, if keeping the 2-relay system, one LED is enough and an on-off switch will be enough, right.

Also, I have read in a page by x3ro, don't remember the link but have the page saved to my disk, that:

"The control side of the OBD-I fan relays have +12v supplied to them only when the key is ON. Therefore you cannot run the fans unless the key is on anyway."

That would defeat the purpose of the switch which is to run the fans while the car is off.

 

So do I need 3A diodes? or will 1A diodes work?

 

You will still need both LEDs if you want to indicate when primary and secondary fans are on. You need the DPDT switch and wire it just like the diagram if you want control of both fans + LEDs.

You are correct that with this method, for pre-96 cars, the key must be ON for the fans to work (engine does not have to be running, though). It is because of the way the power is supplied to the load side of the relays.

 

The original diagram author stated 3a diodes. I think some people have used 1a ones with success. There is very little current on the control side.

 

I have two questions. What are the diodes for, and why aren't they in one linl, but in another? And what is a good power supply for this?

 

Can I just tap into the 12v supply to the cig lighter? I am not too good with electronics, but most of this seems straight forward. Oh yeah, and for the two wires that go to the switch, can each of them be touching where they connect, or do they have to be seperated? Shoebox shows them being seperated, but the other oine doesn't. Thanks guys

 

Yea thats what I did. Its only used to power the LED's so very low amperage.

Craig

 

Which way do I make the diode face? Anode is negative and cathode is positive right? There is a little silver mark on the cathode side. I am guessing that the anode goes towards the cars wiring, and the cathode end goes towards the switch? Is that right?


And is 18 gauge wire big enough? I am guessing it is, since that is what size the led wire is. Thanks guys

 

Well, I got it all done. Thanks for the help guys. I ended up using the 18 gauge, since I didn't hear back from anyone beforehand.