Ford Mustang Forum - View Single Post - Electrical whizzes - help please
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post #10 of (permalink) Old 10-06-2013
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Joined: Jan 2013
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You have the basic idea that you want to use a "switch" on pins 30 and 87 (to open or close the circuit) which will run the fan but that is a high amp (40 amp) circuit which is what burned up your jumper wire.

If you found a 40 amp switch and used heavy enough gauge wire (wire gauge will need to be at least what is running to the fan itself) it would work... but I doubt you will be able to find a 40 amp "switch" that's where the relay comes in...

The relay allows the high amp circuit to be controlled with a low amp switch (5 amp) on pins 86 and 85.

In the stock diagram pin 86 is hot 12v 5amp wherever the key is on (when the PCM is on) pin 85 is what the PCM is using to control the relay BUT you can't simply ground pin 85 (DO NOT DO THIS) without risking damage to your PCM.

So I guess I am not sure how else to explain (sorry I am not a very good teacher)

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