[Mgs] Soliciting advice on an electrical problem

[PaulHunt73]

The switch bodies aren't earthed, any that need an earth to send on to something else like the earlier wipers have it brought in on a black wire.

The heater switch sends out 12v (should be on both green and green/brown with the switch on), and there should be two wires at the heater motor - one for this 12v supply and another for the earth.  As with the pump test both wires - still connected - for 12v.  If you don't have 12v on either then 12v isn't getting from the switch.  If you have any voltage on the earth then the earth is bad.  If you have 12v on one and an earth on the other then the motor should run, so if it doesn't the motor is bad.  The heater earth is wired back to the wiper motor E terminal (for self-parking), which goes to a body earthing point high up in the corner by the motor.

The turn signal tell-tales should have two wires on a Mk1 i.e. your 66 (it's Mk2 up to 71 that only have one wire and the lamp earths via the panel).  One wire goes back from both lamps to a third terminal on the flasher unit, and the other wires go back separately to additional contacts on the turn signal switch.  This is because the tell-tale signal from the third terminal on the flasher unit is normally live when the indicators are not operating, hence the need to switch the earth.  Mk2's got an improved 2-terminal flasher unit and the tell-tales operate in parallel with the lights at the corners of the car.

Only the map light and possibly the dual gauge (although why that doesn't have a wired earth for night-time illumination when the speedo does I don't know) seem to rely on an earth from the dash panel.  All the other items on the dash have a wired earth (again from by the wiper motor) so in theory the dash panel will get its earth from those as well as its physical mountings to the car body.  But as I found with one-wire number-plate lights, given the quality of painting on restoration it's very easy for this earth route to fail even with everything bolted together.

PaulH.


  ----- Original Message ----- 


  With key on I confirmed I have power to the white leads at the fuse box. I removed the radio blanking plate and was able to test some switches. I have power to the back of the heater fan switch, for instance, but it doesn’t come on.


  Are these switches grounded through the dash frame? If they are, I think I know the problem — the powder coat is acting as insulation. The whole thing is probably isolated.
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