Ignition source under the hood?

Ignition source under the hood?

Postby rtb [OP] » August 20th 2012, 4:05pm

I'm trying to wire in an electrical fan and I need to find a power source that tells the fan when the engine is running so the fan turns off when the engine is off. Is the positive terminal on the firewall behind the battery hot only when the ignition is on? If not, then I really don't know where I should be tapping in for this.
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Re: Ignition source under the hood?

Postby chevymaherchevymaher is online! » August 20th 2012, 5:45pm

On the fuse box under the dash there is a single plug which accepts A blade connector. It is marked Ign. It is only on with key on and not acc. Run a wire under the hood through the firewall and attach it to a relay. Gnd the other side of the low voltage side of the relay. On the other 2 connections of the relay. A heavy wire coming from the Common positive behind the battery to the relay. Other side runs to the fan positive. Ground the fan to the common ground on the radiator core support. It is right in front of the battery.

Now with key on you have fan. That is how mine is run. A 94 safari.
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Re: Ignition source under the hood?

Postby Lumpy » August 20th 2012, 6:27pm

A Digital Multi Meter costs anywhere from free to $30 at Freight by the Bay. Invaluable tool when doing any kind of wiring, troubleshooting, anything electrical in your van/home/bomb shelter.


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Re: Ignition source under the hood?

Postby tedanderson » August 21st 2012, 7:47am

X2 on getting that meter. Just because something "should" be a certain way doesn't always mean that it will be that way.
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Re: Ignition source under the hood?

Postby Lumpy » August 21st 2012, 8:07am

I just bought their $30 meter, the green one. It's a fabulous bit of kit, as the Brits would say. I've also got several of their $4 meters, that go on sale for $2, and then become free with any purchase $0 meters once a year. Any of them will work just fine. We're measuring, in this case, "is there 12v or is there 0 volts". And we're measuring continuity. Diode measurement, EBC transistor leakage/gain, dB sound pressure, relative humidity, all that's not typically necessary in anything we'll ever do in an automobile setting.

For use in my onboard tool kit, I had a couple of criteria -
- Meter must shut off with a positive switch, not a pushbutton, to keep from activating while in the tool bag.
- Must be able to measure relatively low impedance (<100 ohms) without activating the continuity buzzer
- If autoranging, must be able to switch to selected range (not auto)
- Must have great probes

The $30 green meter met all of that. There are several variants of that same meter by two manufacturers. They add and drop various functions and features. I thought the HF version was the best of all the options for my setting.


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