First time poster, long time lurker....
I have an 86 GT. I am having an issue with the coolant fan. Approximately 24 hrs after I last drove it, I walked past and heard the radiator fan running. It had apparently been running long enough to drain the battery to the point where I could not use the deck lid release switch to get to the battery. Due to the lock being keyed wrong, i had to trickle charge the battery through the cigarette lighter to get enough juice to open the lid. It took me another 24 hrs to realize I was simply supplying enough power to keep the fan running.

After disconnecting the coolant fan relay, I was able to charge it enough to get the deck open and jump the battery. At that point the fan was not running anymore.

A week later, after it rained, I experienced the same thing ( I cant recall if it had rained at all around the first incident). So this time, after charging the battery, the fan is still running. So I am basically keeping the fan relay disconnected while not in use.

I am looking to you guys with much more experience....clearly I have a short that may or may not be affected by the rain. Aside from possibly replacing the coolant fan relay and/or a/c relay, any suggestions for the cause and solution?

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"We are not now that strength which in old days
Moved earth and heaven, that which we are, we are---
One equal temper of heroic hearts,
Made weak by time and fate, but strong in will
To strive, to seek, to find, and not to yield."

-Alfred, Lord Tennyson

Check the engine temp sensor. It's located by thermostat housing on the block if I remember correctly. It's a single wire sensor. If you disconnect the sensor and the fan stops running that could indicate a problem with the sensor.

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The coil of the FAN relay has switched power on one lead (Brown/White) and gets grounded by the fan switch/AC controls on the other lead (Dk. Green/White). Either the FAN relay itself is bad (most likely) or you have switched power somehow going to the FAN relay AND you have either the A/C set on or the fan switch also went bad.

My guess - try the simplest - replace the Fan Relay.

If you feel comfortable you can also check the pins of the FAN relay. One will have power all the time (Red) - That one is power from the battery. Key off none of the others should have power to them. If you find this, then it really really points to a bad FAN relay.

The fourth wire on the relay (Black/Red) runs to the fan motor.

Another test will be to plug the relay in. If the fan comes on give the relay a good wack. If it then goes off the relay was sticking on.

[This message has been edited by phonedawgz (edited 07-11-2014).]

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[This message has been edited by tshark (edited 09-08-2018).]

Thank you for all the help. I believe I solved the problem.

Another question. I did not notice until after I purchased the car that the temperature gauge was frozen at about the 200 degree mark. Regardless of whether the vehicle was on or off, it never budged. I obtained an extra gauge and replaced it. When I turn on the ignition the gauge moves from hot to cold and then settles at the 100 degree mark; which leads to me to believe the gauge is working properly. Now admittedly, I have not had the chance to road test it a little to allow the engine to heat up properly, but have let it sit at idle with the a/c on for approximately 5-10 minutes and have not seen the needle move. This could easily be a case of not giving it enough time and fortunately have more free time tonight to get it on the road, however....

The question would be, what would be the recommended course of action if it still does not read the temp? Temp sensor? Sending unit? Thermostat?

I am a novice but am learning, if it comes down to having to rewire anything, I would likely take it to someone who knows better.

Thanks again!

http://fierosails.com/tempgage.html

This is a guide on how to fix the temp gauge issue. It does require some rewiring but is very simple to do. If your gauge never moves the wires on your sender unit could be backwards as the plastic plug has probably melted/broken off. Do the temp gauge fix it will save your newer gauge.

Pull the lead off the gauge sending unit located on the left end of the trunk side head. It has 2 green wires. Insert a paper clip and briefly ground each, one at a time. One should make the gauge peg, the other should make the temp light come on. Plug the harness back onto the sender.

If the fan is now working, leave the AC off and let the engine idle until the cooling fan comes on. If the gauge hasn't moved up to about 230 when the fan starts, replace the TEMPERATURE GAUGE/TEMPERATURE LIGHT sending unit. I put that in caps because parts stores will frequently sell the Coolant Temperature Sensor. The gauge sending unit will have a round plastic head with a slit in the side. The CTS will have an oval plastic head. It will screw into the head but won't plug in.

quote Originally posted by fierofool: Pull the lead off the gauge sending unit located on the left end of the trunk side head. It has 2 green wires. Insert a paper clip and briefly ground each, one at a time. One should make the gauge peg, the other should make the temp light come on. Plug the harness back onto the sender. If the fan is now working, leave the AC off and let the engine idle until the cooling fan comes on. If the gauge hasn't moved up to about 230 when the fan starts, replace the TEMPERATURE GAUGE/TEMPERATURE LIGHT sending unit. I put that in caps because parts stores will frequently sell the Coolant Temperature Sensor. The gauge sending unit will have a round plastic head with a slit in the side. The CTS will have an oval plastic head. It will screw into the head but won't plug in.

Thank you for your assistance. Its funny that you mention that the CTS can fit into the Temp gauge's spot. Upon review, I first observed that the wires to the sending unit were spliced. When I pulled the connector, it turned out to be the connector for a CTS and that was what was plugged into the sending unit's spot. Most likely, the previous owner bought the CTS by mistake and assumed that the connector was wrong so spliced in a new one.
I am going to pick up Temp gauge connector today and rewire it for the actual gauge. Hopefully that solves the problem.