Wiring question!

[ecohouse1]

Chaps - I have a general wiring question!

I am going to be wiring in my Radiator Cooling Fan by pass override mod this weekend. From what I can gather the fan relays are permanently live and the Bitron "makes the connection" to earth thereby activating them.

I have a adjustable thermoswitch with sits in the top Rad hose - rated at 20A. This is too low for the 60A load through the earth return wires to the inner wings so I am going to use a heavy duty 70A relay.

Plan is to use the Thermoswitch to activate the relay switch which then connects the big 60A fan load through the earth wires.

Question is can I run a wire from battery +ve to the thermo switch in - then out to the low current relay in - through the low current relay out to earth or would that cause a massive earth/fire! ?????????

Once the low current activates the relay - main earth is connected - fans run (they are currently running all the time the ignition is on - and no amount of checking has shown the fault thats causing it!!!)

[Peter.N.]

You only require a very small amount of current to operate a relay. a matter of milliamps so very light cable would suit, the only heavy current flowing is through the fan itself so the cable supplying that should be fairly hefty. You can easily use a separate earth return, if there isn't an available screw, drill a small hole and use a self tapper.

Peter

[ecohouse1]

Thanks Peter, but is it OK for the supply to the thermoswitch and "relay activating" circuit to come off the battery positive and straight to earth? I can use light duty wire for this or would this be the equivalent of shorting the positive straight to earth?
Sorry auto electrics not my strongest suite!

[dnsey]

If I understand correctly, you propose wiring the thermo switch in series with the relay coil, and this combination between battery positive and earth. That's fine, but it would be sensible to include a fuse (1 Amp is plenty) to protect against faults.

[CitroJim]

Please, please put a fuse in all your new wiring... It's a good guard against an accidental short-circuit or a relay failure causing the wire, especially thin stuff, to heat enough to cause a fire...

A 5A fuse will be good for the relay wiring...

[ecohouse1]

Yes, that's right as I am using the thermoswitch to energise the relay which in turn "connects" the fans to earth thereby allowing them to run. At the moment the fans are running all the time despite changing virtually all the components in the system and checking the wiring. I am setting it up so that the fans only run when the coolant temp rises above 90/95 degrees to avoid constant running at start up and first few miles. Its a Xantia TD BTW

[ecohouse1]

Absolutely Jim - an inline fuse will be used. I did this with my headlamp mod too!
Cheers

[myglaren]

You can get relays with inbuilt blade fuses

[Stickyfinger]

TO keep it neat and tidy, there is room under the relay tray in the fuse box....I added two for my headlamp mod as well as a fused junction box.