Fan switch wiring

Ive searched over and over and would like a definite answer. Possibly FCM can help me out as he seems to be the electrical guru.

Im running dual electric fans with a relay set up to run only with the on position. The car came this way when I bought it and factory fan/ac wiring is gone. What I want to do is instead of grounding directly to the chassis is to use the oem fan switch and run the relay ground to it which is similar to oem wiring so that the fan isnt constantly on. So it would be set up like this this.

relay to +12v constant
relay to +12v switched
relay power wire to fan
relay ground wire to fan switch
fan switch to ground

From what im reading in my helms the “coolant temperature switch”, when heated above 190f or 88.5 provides continuity between the 2 terminals on the switch. If this doesnt make sense let me know.

youshould ask to get this moved into the electrical section. fcm tends to see posts there.

Thanks. If the mods can do this id appreciate it. I figured I would put it here since it falls under cooling systems and oem parts since im trying to utilize the factory switch.

hoping you get an answer i’m watching and curious about this to

that will work. basically instead of putting a manual on/off switch, or grounding the relay which will cause the fans to be always on (like your case), you use the water temp switch instead to activate the fans like it’s suppose to work. you got it all figured out.

although you got some wires mixed up. you’ll be using a standard 5 prong relay.

30 fused 12V hot in run/start
85 12V hot in run/start
86 goes to your water temp switch
87 goes to you fan positive
87a empty
and finally ground your fan motor to the chassis or battery negative directly.

Ok, I will give it a try. Just ordered a new fan switch so well see how it goes.

Redtegra’s wiring looks correct, but it is not at all the way the stock wiring works. I personally prefer to keep things functioning as stock as possible.

If you would like to use a relay, but setup the fan the same way as stock, then you need to set the relay to switch for ground, not power - remember our fan wiring is setup to be a ground switch circuit. In your case with an aftermarket relay:

30: To body ground
85: To #21 fuse (or hot lead of your choice)
86: To YEL/GRN wire from ECT Switch
87: To NEGATIVE terminal on fan motor

#12 fuse to POSITIVE terminal on fan motor

As you can see that’s pretty much exactly opposite of redtegra’s method since the relay is being switched with the ground AND supplying GROUND to the fan motor, not power. This is exactly how the stock fan wiring is setup, so if you wire this way you can trust that any troubleshooting you do with wiring down the road can be trusted to follow the Helms troubleshooting procedures. The above wiring can be confirmed via pg 24-2 in the Helms, and is meant only to represent US spec AC equipped vehicles. Also, be careful with wire colors, in general you can trust what it says in the Helms, but it’s a good idea to check with a multi-meter or test light to confirm. As you can see there’s one wire that changes from YEL/BLK to BLK/YEL - so make sure to read the ENTIRE diagram).

Now that I’ve typed all of that, I’ve got an even better way for you to wire your fan. If you’d like, you can simplify things and do away with relays altogether. Here is how the stock radiator fan is wired for US spec non/AC G2’s (again, you can check against pg 24-2 of the Helms).

YEL/BLK wire from #21 fuse (15A) leads directly to the positive terminal of the fan
YEL/GRN wire from ECT switch leads directly to the negative terminal on the fan

No relays, or extra bits, just plain and simple ground switch circuit. This is how I’ve wired multiple DA/DB’s when removing the AC. (however AC equipped cars get their hot lead from the #12 fuse (15A), so I just use that wire since it’s already in the proper location and was previously used for fan power.)

Lastly, I feel I should mention that some newer Hondas (ITR for example) still uses an ECT switch but the relay is a POS switch circuit. So the fan switch turns the relay ON, but the relay sends power to the fan.

Ok, I get what youre saying. Although, I already have the relay set up that way so all I would need to do is move the ground for the relay to one of the terminals on the ect switch then the other terminal to ground. Seems easiest for me that way. Would there be any issues running it that way? Im more concerned about the fan turning on/off at the proper temps.

That will work fine, there are many ways to wire these things. I personally just like all my wiring to be as stock as possible and as simple as possible even if that requires more work.

Thanks. Im gonna study my helms to see which wires youre talking about. Its gonna take a little more to understand cause my car is a 92 gsr with a jdm obd0 b16a so the ect switch is at the back of the block and the previous owner redid the wiring for it and im not sure its wired. The old connecter for the b17 ect switch is just dangling there.