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MG MGB Technical - Earth/Ground Points

I've recently purchased a 1980 roadster, as my '67 is still in pieces.

Driving it back from Yorkshire, I had a problem with my sat-nav switching off, as it wasn't charging - the sat-nav battery is u/s due to it being 7 years old and not being 'cycled'.

When I got the car home, I checked the voltage at the cigar lighter socket, which was around 11.5v. I also checked it by using one of the screws on the gearlever surround as a ground connection, and the result was nearer 12.5v.

It looks as though there is a high resistance in the ground connection, so I was wondering where the dashboard loom ground is attached to the body.


Dave O'Neill 2

The majority of grounding points for the dashboard, as well as for many other critical electrical components, is located at the base of the windscreen on the right hand side of the car. If you look under the dashboard, you should see a threaded stud with several black wires connected to it. This is a central grounding point. RAY
rjm RAY

Thanks Ray.
Dave O'Neill 2

High up on the right-hand side by the wiper motor.

The earth for all the instrument lighting daisy-chains off the cigar lighter, so if the earth to the lighter is bad it will be to the instruments as well.

You would normally only see a voltage difference between the lighter and a known good earth elsewhere if the lighter (or the instrument lights) were on i.e. some current was flowing. Without that the bad connection would have to almost open-circuit to affect just the meter.

As a 1980 this should have factory installed rear fog lights. If so I'd be grateful if you could tell me if anything else needs to be on for these to work i.e. ignition, parking lights or headlights.
Paul Hunt

Paul,I have a 1980 MGB with original wiring. Rear foglights only come on when headlights on. (The ignition does not need to be on).
Charles
CMD FARRAN

Dave,

Congrats on the new car. I had a similar problem on my 77, and I suspected a dirty ground between the eng/trans and the chassis. On investigation I found that the ground was non-existent. So, you might want to check that.

Charley
C R Huff

Thanks Charley.

Paul, I can confirm that the warning light for the rear fogs only comes on with the headlights. Unfortunately, the rear fogs don't come on at all.

More investigation required!
Dave O'Neill 2

Rear fogs - thanks for that both.
Paul Hunt

This thread was discussed between 19/06/2015 and 20/06/2015

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