I bought a 86 Trans Am. The previous owner pulled the TPI engine and put a carb 305 from an 83 chevy. They did alot of hacking to all the wires. Now im trying to fix all of it. I went to wire the cooling fan up how it would be stock. Well it would be controlled by the ecm but the previous owner removed it. So I bought a fan switch and put it in the head and ran the ground wire to it. But when the switch grounds out it doesnt turn the fan on. I know i have everything hooked up right because i can unplug the switch and ground the relay and the fan works. The switch works because i tested the ground it gives off when the fan switch grounds out from the engine getting to 220f. So my main question is does the ecm give off a stronger ground then a fan switch or am i missing something? Thanks for any help.

 

Do you have one or two cooling fans? An 86 I believe still only has one fan.


Does the fan turn on with the AC on? If it does, then the switch or the wires before the relay are bad as this bypasses the switch.

If you have one fan, the ECM never controlled it, it was only controlled by the fan switch.

I'm assuming the "ground" wire you mentioned hooking to the switch is the one that goes from the switch, up into the wire harness to the relay on the firewall.


With the key in "run", unplug the switch in the head and ground the wire that went to the switch. The fan should turn on. If it doesn't, (you've already verified the switch works at the correct temp), pull the relay by the firewall. It's a box shaped on, probably facing forward with 4 wires coming off of it. It should be easy to get to, just on the outside of the brake booster.

Short the two fat leads on the connector you remove the relay from together. It may spark a little, but, with the key in run, the fan should start. If it does, the relay is bad. Repalce the relay and it should work. IF it still doesn't work, (you said the fan turns on, so it's not the fan motor), there is an in-line fuse on the power wire to the relay that might have blown. Replace that and all should be right with the world provided the relay isn't also bad. Relay's cost like $10.00 so I'd probably go ahead and replace it anyway just to be sure.

Hope this helps narrow it down!

 

Thanks for your response. I should have been more clear. Its a single fan. Previous owner removed the ac. According to the diagrams from the Chilton manual and austinthirdgen.org the ecm controls the fan.

bottom right corner


I bought a new relay already just to make sure. The old relay works beacuse i can ground out the dk grn/wht from the relay and the fan kicks on. So my fan is good. I used my test light and tested the org wire its has power. I tested the brn wire it has power. So everything has is wired right. I know the fan switch works cause i have tested the ground it gives off when it hits 220f.

 

Weird. Might be a bad connection between the pigtail and the switch? If grounding the lead engages the fan, everything works as it should except for the fan switch and/or it's connection. You're testing at the lead's connector to the switch, right?

 

I tested the connection between the pigtail and switch. I cant understand why its giving me such a hard time. Its a pretty basic relay with only 4 wires and a fan switch that acts as a ground.

 

Do you have 12V between the battery and the relay?

 

It has 12 volts one of the first things i tested. If i ground out the grn/wht wire on the body or motor fan kicks on just fine.

 

sounds like the switch is bad

 

Yeah thats what Im thinking. Its a brand new switch but would be the first time a parts store gave me a junk part.

 

Try getting a switch that kicks on at a lower temp. Like a hypertech one. The stock switch that goes in the head doesn't kick on till a much higher than 220 temp. It was originally designed as a backup switch or a high speed fan switch

 

The switch grounds out at 220. I tested it for a ground when it was up to temp and the switch was grounding out. I decided to just buy an aftermarket set up that i can adjust the temp. 220 is a little warm and would prefer it kick on around 180-190 thanks.for everyones input.

 

If the aftermarket one is only a 20 amp, retain your factory relay and wiring and use the aftermarket controller to ground the lead. If you're unsure of the size of the new one, compare wire sizes to stock. Go with the larger.