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MG MGB Technical - Heater fan not running

Hi everyone,
My heater fan on my 1966 MGB has stopped running. I have checked the fan and it works on the bench. There appears to be no current getting to the switch. Fuses also check out OK. I have noticed that the headlight flasher isn't working either which may or may not be relevant. I am trying to chase down the problem and I can't find anything obvious i.e. loose connections etc. Has anyone any pointers as to where I might look for the problem?
P.S. The control box is new, but the voltage regulator is original.
Thanks in anticipation Jim
J Reckitt

Pretty simple circuit - green to the dash switch, green brown from there to the motor, and from the motor on a black to earth.

Test for 12v between the green/brown motor bullet and a good body or engine earth, then do the same from the black at the motor bullets to the brown/purple fuse on the fusebox

If not on the green/brown then check at the dash switch, both sides.

If not on the black then that's the culprit, try and work out where that goes to the body.
paulh4

Thanks Paul. I've got it running again by finding a source of current and connecting it up. What confused me is that on the wiring diagram it shows the current wire for the heater fan coming from the live side of the voltage stabiliser. There are only two wires coming from it on my car, neither of which have any current coming to them.
Any ideas?
J Reckitt

The instrument voltage stabiliser is used as a branching point with one green coming in from the fusebox to feed the fuel gauge, and there should be two going out one to feed the indicator flasher unit and the other to feed the heater switch. If you only have two and the fuel gauge and flashers work as they should, then it would appear that the one to the heater switch is missing as you say.

Is your chassis number before or after 138801 if a roadster, or 139824 if a GT?

I'd expect to see two green wires in one spade connector and a single green in another at the stabiliser, do you have the 'two in one' or two separate green connections?

If you have the two in one take that off the stabiliser and the fuel gauge should stop working, but probably the indicators will still work.

If that's does the heater switch have a green or not? If so can you see a loose green wire floating round behind the dash?
paulh4

This thread was discussed between 17/10/2020 and 19/10/2020

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