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MG MGA - Negative earth and coil connections

Hi all,
I am in the process of converting my car to neg earth. Battery done, fuel pump ok, however I am also told to switch leads on the coil. I dont understand why. I didnt think the coil would be polarity sensitive.
Do I need now to have coil conection marked "CB" having the battery feed and the terminal "SW" going to the points. If this is correct can any body expain why.
Thanks
s page

If you get the coil wiring wrong the spark jumps opposite direction across the plug gap. I still runs, may be a tinny bit lower on spark intensity, might wear the plug electrodes slightly faster.

http://mgaguru.com/mgtech/ignition/ig104.htm

http://mgaguru.com/mgtech/electric/et202.htm

Coils marked +/- are easy, just connect same way as the battery. For battery negative hot and positive earth, coil - to switch and coil + to ground through the distributor points. For battery positive hot and negative earth, coil + to switch and coil - to ground through the distributor points.

Older coils marked SW/CB are the same, just a bit confusing when you switch to negative earth.
SW = "-"
CB = "+"
For positive earth as original, SW goes to switch, and CB goes to the contact breaker points in the distributor (on way to grounding on the engine block).

For negative earth CB goes to switch, and SW goes to the contact breaker points in the distributor (on way to grounding on the engine block). Seems odd, but nothing tricky. If you reverse the battery you should also reverse the coil.

barneymg

Many thanks again Barney. That now does make sense.
s page

This thread was discussed on 09/03/2017

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This thread is from the archive. The Live MG MGA BBS is active now.