Wiring a 12v relay and switch

[andy-xr]

It's an aux fan for the engine, seperate from the thermostat controlled one

This is right, right? It's been a while since I've done one with a 3 pin switch (labelled power/load/earth)

[RizzoTheRat]

Relay's right, not sure what your switch diagram is though. You only need a 2 way switch, open and closed where closed put's 12v on to the relay. No need to earth it.

I'd put an inline fuse in as close to the battery as you can on the power feed, and for the switch it's often easiest to take power from either the head/parking light or the rear brakes switch unless you specifically want it to be able to keep running once you turn the ignition off. ETA: D'Oh, forget that, for some reason I was thinking bikes not cars as that's where most people I know have fitted aftermarket relays.

Edited by RizzoTheRat on Monday 9th June 15:12

[CrutyRammers]

Looks right to me. Does the switch have a lamp in it?

[andy-xr]

CrutyRammers said:

Looks right to me. Does the switch have a lamp in it?

Yes, LED switch and I've got the option of a timer as well. What I'm thinking is I want it running on after the ignition is off, a minute seems a good amount of time just to cool the car off rather than sit there with the ignition on smoking fags, waiting for it to cool before I can leave

ETA - relay is fused one at 30A so wasnt going to bother putting another inline one in

Edited by andy-xr on Monday 9th June 13:44

[RizzoTheRat]

In that case you can get timer relays that latch on for while once you turn them off, eg http://www.polevolt.co.uk/acatalog/info_74205.html

I'm never convinced how effective leaving the fan running once the ignition off really is, it's cooling the water in the radiator but the water pumps not running so does it really cool the engine.

[andy-xr]

It's more to do with heat buildup, I've got some scorch marks on the bonnet because the heat just cant escape, especially when stationary. The relay timing seems a better idea than trying to do it on the switch, cheers for the tip

[RizzoTheRat]

The Quantum I assume? It does look like there's not a lot of airflow to the radiator on them.

[CrutyRammers]

RizzoTheRat said:

In that case you can get timer relays that latch on for while once you turn them off, eg http://www.polevolt.co.uk/acatalog/info_74205.html

I'm never convinced how effective leaving the fan running once the ignition off really is, it's cooling the water in the radiator but the water pumps not running so does it really cool the engine.

Yeah I'm never sure of that. In my Dax it's controlled by the ecu so switches off with the ignition; I've one in the mgb on a thermostat which runs for ages after you turn the ignition off. No idea if one is better than the other though...I can't imagine you'll get any localised heating from heat soak greater than it gets when it's running ?