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MG MGB Technical - Earth lead issues


As I didn't have the benefit of stripping down my mgb I am finding it difficult to determine where the black earth leads should be connected. I am using the wiring diagram but could do with some help with the following

1. My new wiring harness has 3 black wires grouped together and two other individual black wires in the cockpit (behind the dashboard) area. Can someone please explain where these should be fitted?

2. I also have 1 or 2 black wires in the engine bay (near the fuses). Do I just attach these to a nearby bolt (which is screwed into the body itself)?

3. I have opted for a single 12v battery and could do with knowing where on the body to attach the negative connection to. A photo would be most helpful

Many thanks

Alex Davies

Alex - The earth leads can go to any convenient screw hole in the body, but you do need to get all the paint and/or corrosion cleaned from around the hole clear down to bright metal, then coat it with a good corrosion preventative, electrical grease. See article, Electrical Connection Preparation in the Other Tech Articles section of my web site at: Cheers - Dave
David DuBois

Helps to say what year/spec the car is.
The group behind the dash goes on one of the three wing fixing bolts along the top edge - center one I think. On US cars this is immediately above the wiper motor.
The ones in the engine compartment go on a 10-32 screw in the area, usually the same one that retains a loom clip below the fuse box or near the coil. Some cars use more than one of these locations; doesn't matter so long as they reach.
Front lamp earths go to one of the wing fixing bolts forward of rad diaphragm.

FR Millmore

Thanks the car is a 1971 roadster.

I will look for this wing fixing bolt for the cluster of three earth wires.

Do you know where the negative terminal for a single 12v battery should go?

Many thanks,
Alex Davies

UK behind dash earthing point is behind the wiper motor on the bulkhead below the screen from what I've seen, not on a wing fixing bolt. Engine compartment is near the starter relay/fusebox. Both have a threaded boss going through the panel, so if not used for relay or fusebox should be obvious. They have a crinkled surface, possibly to cut through paint to get the the wire tag.

While early headlamps were earthed at a forward point later ones came back to the starter relay point. Chrome bumper parking/indicator lights never had an earth wire but earthed through their physical fixings, same as all rear light clusters.

Single 12v in a chrome bumper car was never a factory option so there isn't a 'proper' place for the earth strap to connect to the body when the battery is on the right-hand side. The most obvious place would be a hole drilled in a similar position to where the hole for the left-hand battery is.
PaulH Solihull

I found all sorts of earth problems after a restoration involving a new paint job inside and out (2 pack). The paint was proving to be a pretty good insulator. For the rear and front light assemblies I fitted unique earth wires just to be sure each globe was well earthed rather than relying on connection through the light fitting base and mounting screws.
John Minchin

This thread was discussed between 14/01/2012 and 19/01/2012

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