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Old 05-24-2008, 01:02 PM   #1
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Simple relay question...

I am debating on wiring a relay to my fan's rocker switch in my '85 CRX Si (the factory thermoswitch gave out long ago.) Anyway, I have plenty of diagrams and a SPDT relay, diode, fuse, etc but I haven't read anywhere whether to mount the relay close to the power (battery or other 12v+) and have long switch wires or do the opposite and have long wires to the relay and shorter ones to the switch. I'm going for reliability and longevity of the circuit. Any other tips are appreciated as well. Mak
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Old 05-24-2008, 01:11 PM   #2
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The best thing to do would be to fix the coolant switch and allow automatic control. But to answer your question is it better to have short power wires and long switch wires. The 30, 87, 87a is the power side of the relay and the 86, 85 is the high resistance control side. So you can use 18 gauge (or even 20 gauge) on the 86, 85 but use at least the factory gauge for the power (30, 87). If the wires have to be long, this will increase the resistance so you should compensate by using a heavier gauge. 16 to 12 gauge sounds reasonable to me.

Make sure you fuse the constant 12v near the source. You can choose the fuse amperage by looking at the stock fuse. It's probably 10A.

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Originally Posted by MakDiesel View Post
I am debating on wiring a relay to my fan's rocker switch in my '85 CRX Si (the factory thermoswitch gave out long ago.) Anyway, I have plenty of diagrams and a SPDT relay, diode, fuse, etc but I haven't read anywhere whether to mount the relay close to the power (battery or other 12v+) and have long switch wires or do the opposite and have long wires to the relay and shorter ones to the switch. I'm going for reliability and longevity of the circuit. Any other tips are appreciated as well. Mak
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Old 05-24-2008, 01:16 PM   #3
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The best thing to do would be to fix the coolant switch and allow automatic control. But to answer your question is it better to have short power wires and long switch wires. The 30, 87, 87a is the power side of the relay and the 86, 85 is the high resistance control side. So you can use 18 gauge (or even 20 gauge) on the 86, 85 but use at least the factory gauge for the power (30, 87). If the wires have to be long, this will increase the resistance so you should compensate by using a heavier gauge. 16 to 12 gauge sounds reasonable to me.

Make sure you fuse the constant 12v near the source. You can choose the fuse amperage by looking at the stock fuse. It's probably 10A.
exactly whayt i was going to say
they only cost about 35 bucks on ebay.
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Old 05-25-2008, 08:40 PM   #4
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I agree, a functioning coolant sensor would fix both my problems (the fan coming on and no need for a relay) but I don't think my switch is broken. About two years ago I completely deleted my A/C (harness, pulley, components, etc) and the fan never worked after that by itself, so I rigged up a toggle switch. I could always have it run whenever the car is running, but that isn't efficient or good on the fan motor. Mak
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