Ignition live source

[ie940]

I have converted my 940 to electric fan but it can enter a bit of a loop where the fan comes on but coolant is not circulating. It's wired to the battery through a relay.

I require an ignition live source ideally in the front of the car so it won't continue with the engine off. Around the turrets, inner wings, headlights would be ideal.

Is there a spare one anywhere?

If not, I've seen two fuses on the passenger turret, are they ignlive by any chance?

[Laird Scooby]

There's a very convenient one in that general area. You'll need a 1/4" piggy back crimp terminal to connect to it and if you haven't already fitted them, a blocking diode in the relay coil feed and a flywheel diode across the relay coil.

What am i on about? The ignition coil of course! Take your relay coil feed from the +ve terminal on the coil with a diode in series (blocking diode) and then the flywheel diode connected across the relay coil, the bar on the flywheel diode closest to the +ve side of the relay coil.

The situation you describe where the cooling fan continues to run at present with the engine not running is commonly referred to as "run on" and for a long time was a problem when fitting aftermarket alarms that worked on the voltage drop principle.
Heat climb within the coolant could bring the fan on a few minutes after leaving the car causing false alarms. Using the switched ignition feed for the relay col gets round this problem and safeguards your battery too!

[ie940]

I've never even heard of a flywheel diode! I'll have to look all that up and see if it is achievable with my below-average wiring skills! Cheers.

Battery drain is my real concern, since the coolant is no longer moving past the sensor in the radiator it feels like it could run on for a while.

[Laird Scooby]

If you've wired a relay up then you can wire up a flywheel diode. Here's an explanation on Wikipedia (to save me typing it all out!) but it's primarily in American English where they call it a "Flyback Diode" - same thing though :

https://en.wikipedia.org/wiki/Flyback_diode

Here's a pack of ten 1N4007 diodes that will do the job very well and can also be used as the blocking diode :

http://spiratronics.com/1n4007-1a-re...ack-of-10.html

If i can find the relevant diagram i'll post it up, i've already done the same thing for another member on here but here's a photo of the blocking diode and flywheel diode crimped into some terminals for easy addition to an existing relay :



Remove the +ve feed to the relay coil from terminal 86 on the relay and connect it to the make spade terminal on the left in the photo, fit the female spade to terminal 86 on the relay. Now remove the earth connector from terminal 85 on the relay and fit the piggy-back connector in its place then fit the connector onto the piggy-back connector.

Job done!

[ie940]

Thanks, it is indeed all very clever. I'll have a read of the Wikipedia page.

I've just realised there is something ready to use that is essentially an ignition live in the headlight area - the sidelight wiring! Haha.

[Laird Scooby]

Good point but if you need to leave the car parked with the sidelights on the fan could continue to run...........