Next on my list of jobs to do is get the rad fans working. I got a new fan switch, and still does not work. Would anyone have a simple circuit how this works? Does the fan switch just switch to earth / -ve, to operate relay in fuse box?
I have tested the fans direct and they run fine. Cheers

 

The relay's coil (usually marked pins 85-86 ) needs power and earth for it to switch on. I use mine with a permanent power on one side, and use the fan switch to control the earth. One side of the switch is earth, the other goes to the relay. The other two pins on the relay are the main feed and the power supply. Imagine a switch on these two, but instead of you toggling it, the relay's coil does it for you, so the switch does not take the bulk of the current used

 

Sounds obvious but have you checked the fuse for that circuit. Sounds like a rewire of the fans is in order as the looms are prone to fail on fan circuits on a Cosworth.

 

You need to rewire the circuit, as said.

The problem is the switch closes too early and then keeps them on for too long, which is what leads to the fuse melting!

For this reason, there are 'uprated' ones available, which are nothing more than just a tighter span.

Another benefit of rewiring is you alleviate the load placed on the fuse box.

Martin

 

Yes fuse fine. Sounds like I need to rewire as said.

On the radiator fan switch, does it matter which terminal is wired to earth / -ve and which goes to relay energising coil?

Cheers.

 

No either one of the terminals to chassis and the other to earth trigger side on the relay .

 

Ford also apparently used the same wiring as a single fan setup plus the long duration switch causing meltdowns of the circuit and even worse affecting the fusebox itself potentially.

 

OK thanks all - will have a look at weekend.

 

I have a fan loom (Motorsport Developments) - not used - pm me if you are interested.

 

You still got it pal?

 

I've got a 12v feed to the rad switch so when it opens this activates the relay. I have a new 12v fused feed to 30 and 87 to the positive terminal of fan. New earths from fan and relay back to battery. I also have an override switch with a feed into 86 to activate the fan manually if needed.

In summary 30 is fused 12v from battery
87 is feed to fan positive
86 is switched 12v from rad switch and/or override switch to trigger relay
85 is earth to battery

You also need to connect earth from fan. Some may do it differently but this works for me.

Hope this helps.

 

Jimbo in your explanation 85 would either need be 12v+ ignition or permanant live . The trigger via the fan switch is -12v earthing the relay to run the fans.
The coil circuit of the relay needs a + and - to activate.

edit-sorry didnt see that you had 12v feed to switch.