Looking for help from the any wiring guru's Need, instructions for wiring a fan relay. Options

[rick 918-S]

I've been working out some of the wiring issues I had as a result of the flurry of activity that occurred while slamming my car together for the WCC 04. I didn't like my home made vacum form fan shroud and undersize (free) Saab fans. They worked ok but they LOOKED free...

I made a real nice aluminum shroud and installed two 14" street rod fans. That was the start of a whole rash of electrical back feed gremlins.

First I overloaded the thermo switch and burned it out which shut down the fans. I replaced it not thinking the added power drain from the larger fans was frying the switch. I burned the second switch in about 5 minuted.

Then I noticed when I pulled the headlight switch the volt gauge would drop to about 10.5 volts and the temp gauge (motor gauge, I have two, one on the motor and one on the radiator) would peg past 250 deg.

When I switched the lights off the gauges would return to normal. I moved the big power lead I had running up to the fans from the back of the fuse panel to the hot lead junction above the fuse panel.

That didn't help the gauges at all. When the volt gauge was reading 10.5 volts I tested the battery with the motor running. Volt metter showed 13.5 volts. That was a good sign.

I ran ground from the volt gauge in the console all the way back to the battery and cleaned (sanded and scraped )and added a star washer to the ground for the other gauges and that fixed the feed back problem.

OK, Back the the fans. I'm still burning fan switches. I want to add a relay like you do when wiring in some big running lights. I have a relay but I don't have a clue how to wire it.

There's a diagram and numbers on the relay body. The parts guy told me it's the same relay they sell for the remote car starters. So I thought that would be a good thing incase it ever burned I could get a replacement easy.

Here's the numbers they look like Bosch numbers.

85 86 87 87a 30

What goes where?

Should I have one relay per fan or will one relay run both fans?


One more update. I drove the car today for about 15 miles though the city without the fans. The car ran at 170 deg. I got into some stop and go traffic and the temp rose to 190 deg. I pulled over and clipped on my jumper wire in place of the burned temp switch. About 4 blocks later the temp was at 180 deg. I jumped on the freeway with the fan jumper still connected and the temp. went to 160 deg. on the radiator gauge and 162 deg. on the motor gauge. Once I get the fan switch relay thing figured out I should have a good cooling system.

Oh, and one more thought on the fan thing. I thought I may install one temp switch on the block to run one fan. And one switch on the radiator like I have now. This way I would start cooling the water when the motor calls for it not when the radiator calls for it. I'm not sure there would much advantage to this as both front and rear gauges seem to show very close to the same reading.