Hey guys, the swap is running great! When I had the drivetrain in the original car the dual fans were wired to run when the car was on-all the time--there were wires in where the relays were-I tried to do it now but the fans come on even when the car is off--am I missing something? What's the best way to have them on when it's running?
Thanks!

 

wire a relay in to the ignigtion key, so when you hit the key a relay ingages supplying votage from the battery to power the fans, make sure you use inline fueses and a good relay.

 

The above post is correct, you should use relays to turn the fans on/off.

Don't use the ignition switch to switch them on/off for having them "on" while the engine is running (I would not want my fans to run contuniously). This is because you'll be asking the ignition switch to handle this relatively heavy load (~30 amperes continuous for both fans, about triple that for the start current lasting a fraction of a second).

As posted above, you should use relays (one 30-40 ampere relay per fan). An "ice cube" type relay should be fine. Ground one side of the coil and use the other side of the coil to be turned on by the ignition switch, where you have +12 with the engine running.

Make sure that the wire powering the relay contacts and fans is large enough to handle this current for the entire length of this run, from the battery terminal to the fan motors. (You'll have one wire per fan/relay, but only one wire powering the common contact for both relay's.)

You probably already know that with the fans running continuously, you'll have a shorter fan motor life than if they were switched on only when needed (but if you need them running all the time, this won't matter). Also, the engine will have to work harder all the time to supply the current that the alternator needs to produce.

EDIT:
Oops, forgot your question "What's the best way to have them on when it's running?".

First, I'd suggest that you have them automatically come on only when necessary. With a stock vehicle, this should not normally be necessary. However, if for whatever reason you need them on all the time, then disregard the following.

For manual and automatic control, wire as described above, but instead of having the ground side of the relay coils permanently grounded, which would have them running continuously with the engine on, have them (one or both) switched to ground. You can do this with a toggle switch (for manual control of the fans) or use a coolant fan switch for automatic control. If you used an on-off-on (center off) toggle switch, you could wire the center contact of this switch to the ground side of the relay coil, the other (end) side of this toggle switch to ground and the third (end) side of the toggle switch to the coolant fan switch, which will be grounded when the coolant temperature gets hot. This will then give you the option of turning the fan off (center position), manually "on" or automatically "on".

If you don't think you'd want to ever keep the fan "off", then just use an on-on toggle switch (manual or automatic operation). This switch can be a mineature switch (Radio Shack) since it will be switching a lot less than one ampere. With a switch this small, you'll have a lot of mounting options.

There is a tech article at this site about wiring fans for manual/automatic control.

[This message has been edited by Stuart Moss (edited July 10, 2001).]

 

Phew! Thanks Stuart for the info. I knew about the fan life being shortened--but that's how it was wired before and it worked out pretty good. Think I'll check out that tech article. Thanks for the answers guys!!