I started wiring in a manual switch for my cooling fans today. I had no trouble finding and splicing into the relay ground wires that go to the ECM. There is a convenient hole right next to the upper door hinge for the wires to the switch. I have a couple questions I couldn't find answers for when using the search engine. I always like to install a red light with toggle switches. The voltage is 12+ on the small ground wire that I am grounding. The first question is: Will this wire carry the current for a small light? Question two: Do you bring on both fans or just the primary or secondary? Later! Frank

If you can post the schematic we will try to help. I don't have one from a 93. I would use a switch that lights up. My 96 has three relays.

I put a manual switch on my 89. Turns on both and use it often. I also replaced that stupid little beannie propeller (aux) with a 14" Tornado pusher.
I too have a lighted switch but ran out of patience trying to make the light work. Will master it some day.
Also put a switch on the antenna so it does not go up unless I need it!

I juat finished doing this.
First, don't use a light, go to radio shack and get a 12v. led. I got one that's only 1/8th in diameter and less than a 1/2 inch long because I didn't want to see it when it was off. The led is really bright when it's on so I can see it when the sun's bright.

Find a hot ( with the key on ) wire, hook that to a 2 amp inline fuse and hook the wire from the fuse to one lead of the led. A 2 amp fuse is all you need, I also use this size for my radar detector hot lead.
Hook the other lead from the led to the same wire that comes from your fan relay to the switch. And, of course hook the other post of the switch to a ground.

I think a better source for the light is to use the output of the relay to the fan motor. If it lights up, you know the relay is sending voltage to the motor.

Yeah, it depends.

The easy way is a light that tells you if the switch is on.

The other way is a light that tells you if the fan is getting power.


The little light is easily powered by the low current side of the relay. If you can't find a lighted switch you like, try some miniature LED lights, painless makes them I used a few in my truck. They require drilling a 1/8" hole.

I stuck my fan switch out of sight near the ALDL plug. It powers both fans on, but only when the key is on. So if I forget and leave it on its no big deal. I would notice next time I turned the car on and heard the fans whooshing with no engine running.

Do the fan relays switch the fan motor grounds or the 12V side?

I recall my fans have fusible links, not a fuse. I don't really like tapping into fat circuits like that for some little bs wiring inside the car, its not as safe IMO.

The computer grounds the relay which starts the fan. I have tapped into both ground wires and tested the wiring. Both start fine. My concern was if the small wire low amp circuit would carry the load. I like a light because I am old and getting a little senile. I don't want to be running both fans any more than necessary. I think you answered my question Coaster. Thanks to all that responded. Later! Frank

I did this mod to my 92 and really like the option to run the fans when I need them. One thing, when the switches are on and you go above 35 mph, you'll most likely get a check engine light.



I can't seem to get this photo to work. ?????????????

Why a check engine light?

Quote:The secondary side of the relay is fed 12 volts from a fusible link. The primary side is hot only with the ignition on. When the computer grounds the primary side, the relay closes and the secondary side sends the 12 volts from the fusible link to the fan motor, which has it's own ground. In short, "the 12V side".

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RACE ON!!!

Right! The wire I tapped into is the relay ground only. Later! Frank

The first question I posted above is: Will this wire carry the current for a small light? In my case the answer is no! I bought a switch with a built in LED. I could run the fans or the light but not both at the same time. The job is done and the fans work fine. Later! Frank

Ha, you gotta be kidding. Those LEDs draw milliamps. You could power one with a wet fart. Anyhow, it works.

On my truck I powered the dash light from the primary side of the relay circuit with no problem. How thin can a wire be that it can't power a relay coil?

Depends on what the resistances of the coil and the led are. The question is voltage drop across the circuit.

For instance lets say they are both 10 Ohms. you would get a 6 volt drop across the coil and a 6 volt drop across the led. As long as each will function with 6 volts, everything is cool. If on the other hand, the coil is 11 ohms and the led is 1ohm, the coil would have 11 volts across it and the led would have 1 volt.

I still say the best way is to draw your 12 V from the motor power. Fuse it at the source.

http://www.tpub.com/neets/book1/chapter3/1-14.htm

Exactly DropTop. Like I said I could run either but not both. Later! Frank

YOU CAN RUN THE FANS AND THE LIGHT AT THE SAME TIME!!!

Oh, so maybe you tried wiring them in series. I'd never recommend that.

I meant to wire them in parallel. Use your dash switch to switch the 12V or ground side of the relay, and the light, using two seperate wires for each part. There's no way that wouldn't work.

Otherwise yeah, you're depending on the relative current draw of each part to have it work right.

Thanks for all the input guys. I found out what I needed to know when I installed the switch. Later! Frank