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MG Midget and Sprite Technical - heating fan troubles

Hi all,

As I am not very good in dealing with electrical problems, I need your advice:

The heating fan in my MKIII (73) stopped working. Fuses are all OK. So I did a quick test and connected the fan motor directly to the battery via starting cables and it is turning...

So the problem must be either in the wires between the switch or in the switch, correct? Everything seems to be fine under the dashboard and in the engine bay, no visible damages etc. So, now the question - does anyone have some experience with this? Where to look first and how to test the switch?

Thanks,
Stepan
Stepan Marek

There should be a ground for it somewhere...clean and tighten it up, next look at any bullet connectors it may have clean and lube those up

If all okay there... Then id get creative with a 12 volt light bulb at the fan switch
Prop and the Blackhole Midget

Stepan,
I've had this problem. Check the wiring on the back of the switch. If the switch gets loosened in the dash, it can twist the wiring at the rear weakening the contacts. Have a fiddle there with the ignition and switch on and see if you can locate a bad connection.
Matt1275Bucks

x2 what Matt said

Also, take a volt meter, and test things at the fan:

the green/yellow wire should have +12V when the fan switch is on - if not, then Matt's suggestion should be your next course of action

the black wire should have 0 resistance to the body ground - if not, then you have a bad ground somewhere


I suspect it will be the switch, though, because the ground point for the fan is shared with a bunch of other stuff and if that was loose there would be a lot of other stuff also not working.


Norm
Norm Kerr

Isn't the heater switch fairly troublesome?

In the past Ive wired (bodged) the dash lights into the sidelamp / headlamp switch, freeing up the dash light switch for the heater - alternatively you could just fix the heater switch!

S G Macfarlane

The switch is troublesome, week and no longer available.
You could just wire up a normal switch on the dash - use the panel light switch as I cannot see a point in that being there. Just don't turn the fan on when the heater flap is closed, although I don't expect it will do much harm if you do.
Dave
Dave Brown

I have spare heater switches you can email me at Richard.woolley@hotmail.com. Richard
rj woolley

Hi Stepan. When you've checked all the easy stuff is OK and it still doesn't work then it may be the motor. I have a 1972 model and this happened to me. Being careful with money I obtained a double fan unit from a mini and cut one fan off. It works a treat now like a new fan
W Clough

Stepan,
shoot me down if I've misunderstood but did you also check the in-line fuse located above the main fuse box that also protects the windscreen wiper motor - easy to check, if the wipers work it's not the fuse
Nigel Atkins

Hi, if the switch is still wired as per the original spec - i.e. it just breaks the +ve feed to the fan then to fully check:

1) Attach a volt meter to the “in wire” on the fan switch. Turn on the ignition. If there is 12+V then the supply to the switch is OK. If there isn’t then there is a problem with the supply to the switch.

2) If there is 12+V supply to the switch then attach the volt meter to the “out wire” and turn on the fan. If there is 12+V then the switch is OK. If there isn’t then the switch is broken.

3) If there is 12+V supply from the switch then with it turned on check the voltage at the fan. If it’s 12+V then the supply to the fan is OK and there is a problem with the earth.

Or a quick way to test the switch is to take the two wires off the switch, join them and turn on the ignition. If the fan starts the switch is faulty. If it doesn't there is a problem elsewhere.

The switch itself is quite fragile and it easily breaks apart - I took mine apart and decided it wasn't an easy thing to fix at home. I think Ashley Hinton had some made up but not sure if they're still available.

As Dave Brown did above, I added another switch and ran the wires through that.




D Griffiths

This thread was discussed between 06/09/2013 and 14/09/2013

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