Auto Electrics 101.

**Farkurnell** · 30-11-2007, 04:05 PM

I just need a bit of electrical advice, as I have no clue when it comes to this subject. My thermo fans are controlled manually by a switch on the dash. In recent weeks the switch has been getting very hot. It totally failed today and I had some overheating issues to deal with on the way home from work. By the looks of things the switch is wired to a direct positive source somewhere as the fans can be switched on when ignition is off. Can someone please explain how to avoid this problem. Is some sort of relay needed. Any help would be appreciated.

Cheers, Greg.

**Dale** · 30-11-2007, 05:49 PM

Search for info on thermo switches, they're what you want.

It will switch the fans on and off as needed by using a water temperature sensor/switch, and if the switch is to fail it should be wired up so that the fans will run permanently.

You could stop your current switch from getting hot by adding an inexpensive relay, but you are much better getting a proper thermoswitch setup to control them

**Sigmeister** · 30-11-2007, 05:58 PM

In answer to your question, a relay is needed. Sounds like the switch is in the direct positive line to the fans and it heats up as they are drawing a lot of current through the switch to the fans.

As stated, you could go a thermal switch, but if you like the manual control, go with a relay. In this instance, the switch would only cause the relay to activate and all the fan current goes through the relay and not your dash switch.

**LeeRoy** · 30-11-2007, 05:59 PM

If you do decide to run a relay then you need to provide power to pins 30, and 85, The main power will go into 30 then just run a small wire across from 30 into 85. Then from 87 run that wire to your thermo fan after which it will exit and need to be grounded. Pin 86 will run a return wire to your switch which controls the thermos following by a ground.

If you run it this way, main power runs between 30 and 87 which controlls the thermo and is opened by closing the circuit (through the switch) and allowing current to flow between 85 and 86. This may also be useful even if you have a thermo control unit with a temp sensor and that doesnt have a relay because by the sounds of things the wires used on your thermo have been getting way to hot (drawing too much current) and have finally given up.

A thermo control unit will simply turn the thermo's on and off but your switch in the car will act as a master switch so unless this is on, the thermos wont work.

See this relay pic if u dont understand the pins thingy Fan Relay

EDIT: In this scenario it is a negative switched setup. Alternatively you can have the in cabin switch on the power side and then run two grounds out of the relay (one from 86 and one from 87) - whereas in the setup i first described, pin 86 goes to the switch.

In the majority of circumstances this is how relays are setup. Toyota headlights are the same in that they use a ground in the switch to select hi and low beam.