The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Fan Relay —selection/wiring

kipps · 03-04-2019, 06:46 PM

Re-reading your first post, the temp switch grounds out when it wants a fan to come on. Thus, D and E would be connected to the temp switch and an ignition hot. Which one is which doesn't matter. The reason for an ignition hot, is so the relay and fan shut off when the key is turned off.

A and E would be connected to a fused battery hot and to the fan hot. Again, the order doesn't matter. C would be ignored. The fan would be grounded through conventional methods.

A possible method of wiring A and E would allow for easy testing of the fan. The stock application does that for testing the fuel pump. Note that if 12 volts are applied to C while the relay is off, the attached fuel pump will run. This feature could be applied to your situation, though I doubt there's much point.

An unrelated but amusing sidenote:

Yesterday, I was tracing the stock 2010 wiring on a Tahoe fusebox/wiring harness/ECM that I picked up. It turns out the ECM on this LS engine sends two ground signals to three relays, which in turn, operate two fans. If A is grounded, fan #1 turns on full speed. If A and B are grounded, fan #1 and #2 operate in series, thus both are turning slow. If B is grounded, both are running in parallel, and thus turning full speed. It's amazing the gymnastics you can accomplish with five-pin relays.

03-04-2019, 06:46 PM	#7
kipps Registered User Join Date: Jul 2014 Location: North-central Virginia Posts: 1,099	Re: Fan Relay —selection/wiring Re-reading your first post, the temp switch grounds out when it wants a fan to come on. Thus, D and E would be connected to the temp switch and an ignition hot. Which one is which doesn't matter. The reason for an ignition hot, is so the relay and fan shut off when the key is turned off. A and E would be connected to a fused battery hot and to the fan hot. Again, the order doesn't matter. C would be ignored. The fan would be grounded through conventional methods. A possible method of wiring A and E would allow for easy testing of the fan. The stock application does that for testing the fuel pump. Note that if 12 volts are applied to C while the relay is off, the attached fuel pump will run. This feature could be applied to your situation, though I doubt there's much point. An unrelated but amusing sidenote: Yesterday, I was tracing the stock 2010 wiring on a Tahoe fusebox/wiring harness/ECM that I picked up. It turns out the ECM on this LS engine sends two ground signals to three relays, which in turn, operate two fans. If A is grounded, fan #1 turns on full speed. If A and B are grounded, fan #1 and #2 operate in series, thus both are turning slow. If B is grounded, both are running in parallel, and thus turning full speed. It's amazing the gymnastics you can accomplish with five-pin relays.