Cooling fan wiring

[paddy]

For a start, I think it is OK to leave it wired as it is. Having the current go through the ignition switch is not a big issue I think, because on the whole the ignition switch will only rarely be doing the switching - they will be switched on and off via the thermostatic switch.

That said, I personally prefer to have the fan able to run without the ignition, so I think you are right to consider it.

So, your decisions are:

1) where to find the source of power
2) whether or not to fit a relay
3) whether or not, and where, to fuse it.

For (1), I think your choices are:

a) get power from the main termination on the solenoid. This is where the main feed goes from the battery, and where the rest of the loom gets the power. This is what I did when I replaced my loom, adding a new thick brown wire from here to the front of the engine bay, which supplied the fan and also the headlamps (because I switched them over to relays at the same time).

b) pass a wire through the bulkhead where the loom goes through, and connect to a permanently live source somewhere behind the dash. This option is the least intrusive but is harder to do with the dash in place. You could run a wire to the ignition switch itself and connect to the unswitched wire that feeds the ignition switch.

2) If you don't already have a relay and you are rewiring the fan, I would recommend fitting one. The thermostatic switches are not really designed to carry or switch high current. I fitted a relay at the front of the engine bay in the same area as the headlamp relays.

3) You don't have to have a fuse - and almost all of the wiring in the car is unfused - but you are safer with a fuse in the event of a short-circuit failure in the fan. You also get some protection in the case of accidental damage to the wiring but unless you're going to rewire the car I think you're only really giving yourself a false impression of extra safety. A fuse, on the other hand, is a potential source of failure, but nowadays it is unheard of for them to just fail if they are rated appropriately. If you have a fuse, make sure it is accessible so you can check it easily.

I used a relay with an integral fuse like this one:

http://www.holden.co.uk/displayproduct. ... de=080.801

So the wiring you need will be:

i) run the unswitched power to the relay. This will be to power the relay itself and the fan. If you use a relay like the one in the link, connect this to both terminal 30 and terminal 85.

ii) connect terminal 86 to the thermostatic switch. The other side of the switch connects to earth. Having the switch in the earth side of the circuit defends against an earth fault in the switch itself.

iii) connect terminal 87 to the positive side of the fan;

iv) connect the negative side of the fan to earth directly.

If you choose to have a separate fuse, it will go inline somewhere in wire (i).

Paddy

[Galwaylotus]

A relay is a switch operated by a magnetic coil.
The coil part of the relay can be connected either way round and it is a low power device that can be fed from the ignition switch usually through a fuse.
The switched side should be fed by a cable rated to handle all the power of the load and as short as possible from the battery. Again, it shouldn't matter which of the "switched" terminals is used as it's simply a switch. The other terminal goes to the load (fans in this case) and they must be earthed. The switched side of the circuit should also be fused - can be an in-line fuse if you wish to keep the cable run to a minimum.
Modern relays of the Bosch type have the circuit marked on them. 85 and 86 are the coil terminals and 30 and 87 are the switch terminals.
Hope this helps!

[Galwaylotus]

Oops! I was composing and sending my reply when Paddy was posting his! I ony saw it when I posted mine.