I have dual fans in my car but I am running a FAST ECU with engine harness along with deleting my A/C so now my secondary fan is rendered useless. The FAST system controls the on/off operation of the primary only. Now its proberbly not safe to just splice the secondary fans wires into the primary fan cuz Im willing to bet that the wires and relay couldnt handle that much of a load. So, it looks like I will have to somehow run the second fan on its very own circuit with me being in total control of it through a switch. What would be the simpliest way to do this without having to run all new wiring? Is it possible to just tap into that fans relay and run a few wires to a switch from their?

Oh and I also have a complete single fan setup sitting around that I bought a while back. Would it be better to use 1 big single fan or rigged up my second one?

 

IMHO there are a couple of options here. And I assume your factory fan harness hasn't been removed.

One, connect the FAST fan control wire to both fan relays. Then both fans will run at the same time and the load will be distributed.

Two, connect the Aux / Secondary fan relay trigger wire to a temp switch that gets installed in the cylinder head. This is the way the factory does it.

Three, connect the Aux / Secondary fan relay trigger wire to a manual switch inside the car.

I like option 2 the best because its provides some redundancy if the FAST unit fails and it doesn't require you to constantly watch the water temp like a manual switch does. Leaving the fan on constantly puts unessesary strain on the Alt. and defeats the purpose of electric fans.

 

I cant do option 2 because I do not have a way to mount another sensor in the head. I already have one for the gauge in the drivers head and the one for the FAST setup is located on top of the intake becuase the spot on the passenger head where it belongs is way to close to the headers and I always seems to burn the wire and tip of the sensor of after 1 day of driving.

 

All you really have to do would be to get one of those electric fan relay kits that comes with the relay, wiring and sender. Hook up the relay to the battery and fan, and when it is time to wire up the sender, just splice into your other fan temp sender and it should work. The only problem is that you won't be in control of when the fan will come on because that wiring configuration will turn on both fans at the same time.

 

actually, I was just gonna jump the power from 1 relay to the other and hope that both fans turn on at the same time. I have total control of when the fans turn on and off. All I have to do is tell the ECU what temp to turn them off and on at. If the temp gets to 200 and I want the fans to turn on at that temp then with both fans coming on at the same time, then the both wont be on a long as just 1 fan trying to cool the engine to say 180 before they turn off. Im gonna have to look at the wiring I did for the primary coolant fan relay to the FAST setup.

this is straight from the FAST directions. "Fan (-)
Connect this wire to the negative side of a relay used to power your fan (relay not included). This output switches to ground when active. Use this wire to activate the negative side of a relay, and use the relay to provide power to the fan. Do not connect this wire directly to the fan or to a 12 volt source or ECU damage will occur! Fan control is available on bank-to-bank systems only. " I know I had ot make a few other wiring changes tothe relay to get it to work correctly.

 

basically just use the 12V+ off the fans primary relay to power up a secondary relay to turn on the second one. this would be the easiest way possible. I would recommend relay part number MR-78 from murrays or advance auto parts. it is $17.99 for the relay and has a bracket on the top to use a sheetmetal screw to mount it on the firewall. 5 simple wire hookup and you're set. PM me if you need any help with it.

 

what about just using a small jumper wire from one relay to another.

 

I think that the problem is that the fan relay is only able to safely handle the load of 1 fan. If you use a jumper wire you are allowing the second relay to pull all of its power through the first one, and can result in failure of the relay.

 

1. Splice 14g wire from Primary fan output
2. Splice to input COIL on Secondary relay.
3. Enjoy dual fans.

an extra 10ma load on the primary wont cause a single problem.