Electrical relay help needed-

I want to rewire my electric fan(s) in the engine compartment, but I'm not sure how to do it. I want the fans only to come on when the ignition is on, but they are also run by thermostat that turns them on when the temp hits a pre-set point.

I don't want the ignition wire to power the fans by itself, I'd rather have a more direct power source rather than trying to run a large enough wire and fuse all the way from the fuse box.

Basically what I want is a relay that will only turn on if and when both (ignition and temp sensor) inputs are powered, but still power the fan through the battery (fused at the battery). I assume there is a relay that will do this? Where would I find it and what is it called?

Thanks-

Pretty much any relay will do the job - just depends on what you're really trying to do. Do you want the fan on all the time the key is on? Do you want the fan power to only be available with the key on, but you still want control over the fan operation?

All you really need to do is take a "feed wire" from some "keyed" power lead, and use it to trigger the relay. Or, take the same lead, break in a switch, then the fan will work only when the key is on AND the switch is on.

We need more information to give you a better setup, and a year would be a HUGE help if you want more specific advice...

5-90

5-90 said:

Pretty much any relay will do the job - just depends on what you're really trying to do. Do you want the fan on all the time the key is on? Do you want the fan power to only be available with the key on, but you still want control over the fan operation?

All you really need to do is take a "feed wire" from some "keyed" power lead, and use it to trigger the relay. Or, take the same lead, break in a switch, then the fan will work only when the key is on AND the switch is on.

We need more information to give you a better setup, and a year would be a HUGE help if you want more specific advice...

5-90

Click to expand...

Year is a '92, but none of this is stock. I want the fans only to come on when both leads are "true", or both the key is on and the temp sensor is activated. If the temp is high but key is off, the fan should be off, and likewise when the key is on and the temp is low, fan should be off.

Right now I have a crappy fan controller that runs straight from the battery. It has a power lead (from batt), temp lead (to radiator) and the output power to the fan. Maybe just run a relay to the ignition to power the controller? That would be pretty simple.

The fans are my e-fan replacement for the mechanical fan and the 10" fan I mounted under the heater core in the hood. I'm rewiring the entire set-up this week and re-building the core and 10" fan mount on the hood.

Sounds like you just want to make an AND logic gate using relays. Get 2 relays that can handle the load of your fans and connect them like this:

Assuming your fans are always grounded, wire the relays in series to connect your fans to 12V of the battery, so something like this...

12V battery - normally open relay closed by ignition signal - normally open relay closed by temp signal - fans

Here is my crude drawing. This should work for you. Main battery to relay 1. Ignition/acc will trigger first relay, passing power to second relay. Second relay is off until the temp sensor in the radiator triggers it. Once it's triggered, power is sent to the fan. This way though, even if the temp is high, the fan cannot come on unless the key is turned.

Make sure you use some beefy wiring for main battery input and outputs. Also you'll need to find some relays that can handle the current you intend to pull through them. You don't want to be blowing these relays on the trail.

clint said:

Here is my crude drawing. This should work for you. Main battery to relay 1. Ignition/acc will trigger first relay, passing power to second relay. Second relay is off until the temp sensor in the radiator triggers it. Once it's triggered, power is sent to the fan. This way though, even if the temp is high, the fan cannot come on unless the key is turned.

Make sure you use some beefy wiring for main battery input and outputs. Also you'll need to find some relays that can handle the current you intend to pull through them. You don't want to be blowing these relays on the trail.

Click to expand...

Thanks Clint, I should be able to get this wired up shortly now. (I can read a stick figure drawing )

I hope it helps. Where did you pick up the relays?

Um, I'll pick them up tonight. I have a NAPA and a Radio Shack near work, any other ideas? I work in Woodscross/Bountiful

Depending on your radio shack (the one out here blows) That might be a better option. The Napa here won't just look up relays without make/model. (they suck)