chevyo3

I have a 87 SC with 305 (LG4 4bbl). The problem I am having is that the electric fan relay switch keeps melting red wire going to it. This shuts my fan off ,and my car overheats. I believe this wire is my hot wire. I spliced the red wire back together ,and electrical taped it ,but it continues to melt apart. I have heard this can be bypassed at the sensor in the cylinder head,and wired to a switch inside the car. Has anyone else had this problem? Can the fan be wired to come on automaticly when the car is started?

deadbird

The thicker red (usually orange) wire comming into the relay should be direct power from the battery. The black (heavy gauge too) wire from the relay goes to the fan. The green/white stripe wire going to the relay is ground from either the ECM or the fan switch (or both, fan setups differ). The tan/white stripe is a 12v switched power source. If you ground the green wire the fan will come on (and stay on) with the ignition.

Have you checked the fan to see if it spins freely ? Sounds like something is causing excessive resistance making the wire get too hot. How thick is the red wire from the battery to the relay ? I needs to be at least 14ga. (IMO).

chevyo3

The red wire or orange is 14ga. My fan did get stuck once ,and I corrected that. That must be what burned the wire thru. I wanted to re-turminate the red wire ,and replug to relay. The wire burnt thru write at the relay. I'll try grounding the green wire if its easier.Do I need to bypass sensor in the cylinder head? Will the fan shut off when car is shut off?

92RSB4C

Is it the red wire going from the battery to the relay, or the red wire going from the relay to the motor that's burning thru?

chevyo3

I believe the red wire runs to the battery ,but not sure. One thing I do know is that it must control the power ,because when disconnected the fan does not run. I sure wish I could read wiring diagrams.

deadbird

Awhile back I made this (atached below) to show someone.

You'll have to ignore the 20a inline fuse, factory fans are on a fusable link (shown in pic too).

The green wire with the white stripe is what you can splice a switch into (or just cut & put on a switch) for personal control of the fan. Even if you leave the switch on, when the car is turned off, the tan/white stripe wire no longer has +12v on it making the relay switch off.

Your fan may also have the fan switch on the ground (green/white stripe wire) too or, might not be ECM controlled. Either way it goes, the green/white wire should be present at your relay.

chevyo3

What about the temperature coolant sensor? My camaro book shows ECM haness going to it. I had to replace the sensor to get the fan to work before the red wire burnt threw. I noticed your diagram didnt show the sensor. Will your fix still apply with this info provided? What gauge is the green and white wire? What kind of switch would you recomend? Where would you locate it?

deadbird

I didn't put a the CTS on the diagram since it not aphysically direct connection to the relay (unlike a fan switch). The CTS (coolant sensor, on your thermo housing), is what the ECM uses to tell the temp of the car. When the ECM 'sees' the temp from that sensor it's supposed to for turning on the fan, it grounds out the green/white wire. The same thing happens (basing this on my car here...) when the A/C is turned on. There is a little pressure switch on one of the A/C lines (rides the frame rail, pass side) that also let the ECM know when the A/C is turned on. This will also cause the ECM to ground the green wire.

Since the wire is only a ground, there's no real worry about adding a ground of your own inline with the existing wiring. The green/white wire should be around 18-20ga (like the majority of wiring to the car).

The switch & placement you pick is of your own personal preference. The power required to switch a relay is pretty low so you don't have to have one of those big, light up, 50A switches you see at Autozone. Picking up a small metal toggle or black rocker 5A switch from Radio Shack would most likely be sufficient if you're looking for something discrete.

Hope my rambling was somewhat clear enough. Made a real fast diag for you too just in case...

*edit... I suppose I could've just modified the original one I did... duh lol

chevyo3

Thanks for your help. The diagram was perfect.

pandorafowler

So you could take the green/white wire and ground it onto the block and it will let the fan run when the engine is switched on?