I am troubleshooting a non-working coolant fan on my '89. Following the steps in the FSM I replaced the fan motor. When that fan didn't start I bench tested the old one and found it to be good. Fast forward to my issue... When testing at the relay "socket", on the driver's side wheel well, good news, I get 12 volts from the red wire, battery voltage. When I jump 12 volts from the battery to the black wire, to the fan motor, it runs. But I can't for the life of me get the fan to run when I put a jumper wire from the red wire to the black one.

The jumper wire gauge is adequate. I am getting good contact. The FSM says to use a fused jumper but I am not. I am using a straight wire, no fuse, so I have it as simple as I can. I switched relays with the auxiliary fan and found the relay to be good.

Any suggestions?

 

Put your voltmeter on the line when you have the jumper installed. You will probably find that the voltage falls to zero when a load is applied. Crappy connection somewhere, very likely in the relay socket.

 

You are correct and now I can stop caning myself... Lucky for me the only thing upstream is the fusible link. If you make it to Hawaii let me buy you a beer.

 

Way to go Shuey!

 

There is always 12v present at/within the relay...all the relay does is ground the other end of the circuit. By putting a wire across the red and black you are shorting out the circuit without actually closing the grounding point which completes the circuit - so the fan doesn't run. Your relay or ground wire may have issues.

 

According to the diagram that I have, the circuit is a straight shot from the power source through the relay through the motor to ground. The ECM activates the relay by grounding the coil side. The OP is jumpering the output side, so the fan should indeed run. He is simply bypassing the relay.

 

Not tryin' to get into a pissin' match here - The way the OP's post reads he is jumpering the wrong wires together. Here is the "jumper" wire thing in a nut shell w/o cracking open the FSM:

If everything is connected properly on the car and the key is in "run" you need only to put your "jumper" on the fan's grounding wire (whatever color that might be) to any known good grounding source other than the fan relay....if 12v is present on the other leg of the fan - the fan should run - if the fan motor is good. If your still having problems look at connections, the relay, or grounding points.

Always use a "jumper" wire with some type of "load" built into such as a light bulb or fuse. Fire or short circuit can result if you probe/test/jumper the wrong wires together without a fuse or some other load in-between the test points.

Sounds like you've got a handle on it. Good luck.

 

This is the diagram I am going by, and it seems to coincide with what the OP is saying. He is jumping the red wire from the fusible link to the b/r (he called it black) and thus powering up the motor. How could it be any clearer?

 

I'm pretty much finished with this thread since we have to "read into" what the OP is saying but in the interest of helping the OP I'll post this last entry into this thread.

The description of what the OP gave and did as described in post #1 may be part of why his fans don't currently run. Clearly the OP had an issue with the fan circuit before he started jumpering stuff....whatever that issue might have been we'll have to leave it to the him to elaborate on in future posts.

Below in pic #1 is a legible GM FSM schematic for a 1989 Corvette....if you don't have a GM/Helms version I highly recommend picking one up. The portion of the main fan circuit were are concerned with is what is pictured.



Here in picture #2 if you jumpered from "red" to this "black" (438) or "black/red" (702) your OK...no harm done. Jumpering 12v to "black/red" should have made the fan motor run if the other motor leg was grounded....as CF member M Shumocker suggests.




Below in pic #3 you can see why jumping the "black" (151) wire to the "red" (or any red) wire is not a good thing to do with an unfused jumper wire. Basically with the jumper wire in place 12v is going straight to ground bypassing the fan motor entirely...and shorting the battery voltage straight to ground. If this is what the OP "jumped" with an unfused jumper wire more than likely fusible link "D" is blown....which powers the fan motor circuit normally. You may need to check to ensure that you still have 12v on both sides of the fusible link "D" before you continue your troubleshooting.



Maybe the schmatic will help if nothing else does. In the future, with a properly functioning fan circuit, if you want the fan to run turn the key to the "run" and connect your "jumper" into the fan's relay grounding wire "green/white" (935/335) wire to any known good grounding source...and the fan should run as long as the jumper is grounded or until the ignition key is turned off. Another option is to apply a fused 12volts to the "black/red" (702) wire.

Good luck,

 

The op was talking about jumping at the relay. The black wire you refer to is the ground leg of the fan motor and not accessible at the relay. the black wire the OP refers to is the power to the coil of the relay.

What he learned is that you can read batt voltage on a open circuit even with high resistance. Once you complete the circuit, the voltage drops to zero or thereabouts.

 

You were correct, the fusible link was 98% gone. I was not able to find the replacement fusible link so I replaced it with a 20 amp in-line fuse, in a weather proof housing. I jumped the ALDL and the fan kicked in as the FSM stated it would.

Thanks to all that offered advice. In the future I will try to use the correct / specific terminology to minimize the confusion.

 

Glad you solved it.

Your problem has spurred me on to look into my 96. It is setting a code whenever the cooling fans kick on. Not causing any problems but annoying having the light on all the time.