15 replies to this topic

[Rubbershorts]

Hi all. My auxiliary fan has a toggle switch on the dash for manual operation. The holder is a bit scrappy and I've been given a replacement by the old guy at the MOT garage. Back in the day he used to have these hung up on a tear card as he said car owners back then used them all the time. It was such a nice gesture I'm set on using it so it's there next time I see him. The current switch needs around a 14mm hole, the switch holder he gave me is nearer 12mm. I don't really want to drill it out. I need a replacement switch but don't know what amp rating I need. Anybody know? Daz.

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[bangermadness08]

I had someone techy install a fan switch, from memory it was a 13a inline fuse if that helps.

[floormanager]

You'd normally wire the fan through a relay, so the amperage going through the switch is small, something like this:-

 

 Fan.png   305.94K   3 downloads

[Ethel]

More than the wire, or fuse, is rated. Floormanager's info seems on the money 14awg is 2mm²  The fuse will also be what a blade fuse will be marked.

 

You might want to consider the terminals (1/4" spade?) & whether it illuminates too.  

[Rubbershorts]

Cheers guys, this has,as usual, turned into something else. The manual switch to the sensor on the bottom corner of the radiator, has neither a fuse nor a relay that I know of. Previous owner fitted the switch so I'd have to pull it all out to be 100%, but the wire isn't really hidden so I doubt there is. Serious question, how bad a bodge is that?
The battery is disconnected when not using the car, so not in flames at the moment.

[Ethel]

Is it not using the original wiring, if there was a thermal switch? Stalled motors  don't have much resistance, so a fuse is always a good idea where one is involved.

 

Putting a relay in place of, or in tandem with, the thermal rad switch would be the easiest way. You could then tap a live for the manual switch, to operate the relay, of pretty much anything downstream of a fuse. The heater fan switch would be easy, with a piggyback spade.

[Rubbershorts]

Thanks Ethel

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Edited by Rubbershorts, 27 May 2025 - 05:46 AM.

[Rubbershorts]

Thanks Ethel. This pic is just something I found on my phone, as I can't get to the car at the moment. Two red wires piggy backed onto the spades then run into the cab to the above pictured switch.

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Edited by Rubbershorts, 27 May 2025 - 05:45 AM.

[Rubbershorts]

Double post due to the current server issues. Evidently succeeded when it said it failed.

[Rubbershorts]

So this is how it's wired. The switch is on the end of these two large red wires, and when activated simply bridges the two contacts. Is this very wrong/unsafe? If so, how do I rectify it?

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[sonscar]

Looks like the switch is only doing what the temp switch should be doing.This should be operating a relay.Turn on without running engine and listen for a click when you operate the switch to find if this is so.If it is it should be carrying little current and should be ok.Steve..

[Rubbershorts]

Thanks Steve, much appreciated. No sign of a relay. Just to clarify, the temp switch still works but the previous owner fitted this aux switch as he had plans to move the car abroad and wanted a back up should the temperature one fail on the way. The temperature activated set up is from the factory so I'm presuming it has it's own relay? If I need to, how do I introduce a relay to into these two red wires? Could it just be fused?

[sonscar]

You would have to trace the wires to find their destinations,using the thermoswitch to control the fan without a relay is asking a lot of it.Floormanager posted a diagram of what you need to achieve.Be careful as overloaded wires cause fires.Steve..

[stuart bowes]

Is there any indication of wattage on the fan sticker?

Wattage divided by 12 (volts) = amps

Or to put another way, on a 13a fuse you can handle up to about 150watt

You could also set it up in series with a voltmeter and run it up for a few seconds reading amps, see what it pulls

Edited by stuart bowes, Yesterday, 07:01 PM.

[Ethel]

Is it not already switching a relay? I thought there was one on the aux fan circuit, or is that only the injection models? 

 

 

...The wiring diagram I've got (not sure if it's only SPI, but don't see why it'd be any different) shows the radiator switch switching the coil of the motor relay to earth. A light green/white wire coming from terminal 85 on the fan relay. If that's right, you'd only need a single wire to the dash switch, that the switch earths. 

 

The relay should be on the bulkhead to the left of the wiper motor - a bit of neater place to tap off for the switch.