V6 Conversion-relays-How to Install
 

My project has been dragging due to lack of knowledge and Spring is on its way. The engine runs, the fan works, and I have instaslled a Mallory electronic ignition. I need to install relays and have no idea how to install them or even what there purpose is. I know that I need one for the radiator fan.
I would like to know what else should have a relay and if possible how they should be wired. I bought relays at a local electronics store and they happen to be Bosch. I have both the relays and the wire ends (female). Thanks in advance. Pete

A relay is an electrically-operated switch. There is an input, an output, and a pair of control terminals. When current flows through the control terminals (when one is hooked to ground and the other is hooked to power), the relay closes the switch and shorts the input to the output. This is done to make the large part of the electrical load pass through the relay instead of whatever switch you have controlling the relay.

The relays in our 914s (the round ones) follow what seems to be a pretty standard Bosch numbering scheme. The input is terminal 30, the output is terminal 87, and the two swtiching terminals are 85 and 86.

You hook up a big fat wire (that comes straight from the battery, hopefully!) to #30. You hook up another big fat wire from #87 to whatever you are controlling--the fan, in this case. You hook up #85 to a "switched" 12-volt source, that is a circuit that has power when the key is on. Then you hook up #86 to whatever is supposed to turn your fan on and off, presumably a heat-operated switch. When the switch closes and shorts its wire to ground, that will complete the circuit through the relay's coil. That will in turn cause #30 to be connected to #87, sending power to the fan.

Make sense?

If your fan switch does not supply a ground, but rather supplies power, then you can still connect it to #86. You would instead hook a ground up to #85, so that when #86 got power it would complete the circuit through the coil, yadda yadda yadda.

I think I have a write-up with pictures of the way a relay works... Yeah, it's partway down this page: http://members.rennlist.com/damp_dave/electric.html

That may give you a better idea of how a relay works and how you would wire it.

--DD

Dave," you da man ". Can you please suggest what other items typically need a relay. Thanks

Anything that draws a lot of current, pretty much. Pumps, high-powered headlights, fans... Usually high-powered stereo amplifiers effectively have a power relay built into them, so none are needed there.

If you want to set things up so that X has to be on before you can turn Y on, relays work well for that. (The stock FI fuel pump circuit is an example; the ignition has to be on to enable the fuel pump to be on.)

--DD