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FYI-How to find out if you MG is pos ground

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M

mightymidget

Jedi Knight
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As I mention I purchased a dead 67 MG Midget, and was wondering how to know for sure if it was postive earth, or if it had been switched over.

1. Electric Fuel Pump will only work if battery is hooked up correctly.
2. How the coil wire is hooked up to distributor, coil neg leg to distributor for negative ground cars

I am sure there are more, but these I have found once I started working on car
 
Unless someone swapped coils trying to get it to start, and possibly a fuel pump.
SU Pumps, often, if connected backwards, SMOKE.
I have seen some with coloured tape around the parting line to indicate internal polarity.
 
I thought I read somewhere the pumps are color coded for polarity, blue means positive earth or something like that? Don't quote me.
 
That's the tape.
I THINK mine was red.....and it was part numbered "positive ground", for a car converted to negative.....and it was toast, yet only 6 months old.
The polarity-sensitive part inside (diode for arc suppression, I think) is a blackened mass, and the plastic that held it was melted pretty good.
 
tomshobby said:
Check your battery cables. Does the cable on the positive post or the negative post go to ground.
Click to expand...

:lol: I was going to say that earlier but figured It was too mean. I assume the owner has a car that came with no battery and he wants to figure out the ground before he puts one in.
 
Along similar lines, though, the battery cable ends are usually different sizes becuase the posts of the batteries are different sizes for negative and positive. Trouble is, I can't recall which is the big side and which is small.
 
If you had followed this saga, he bought the car, actual year and marque is under discussion.
It was grounded wrong for what he THOUGHT it was, but maybe not for what it might end up being.

He was trying to figure if the PO had hooked up correct or backwards.

Quite a thread, it was.

Oh......battery cables not necessarily different sized...when new replacements are installed.
That happens once you tighten them down (not the "hat" style).

To give you an idea:

My LBC is a 1964.
Originally positive earthing.

Ah, but it was negative earth when it arrived on scene.
Now, I am not going to just swap parts or polarity until I KNOW what is up.

Good thing, too.

The car had AC, as it was from Singapore.....
When I yanked the AC out several months after I started driving it, lo, and behold, there was a Lucas Alternator under the compressor, NOT the Generator I would have imagined (stock).

Had I just swapped around cables, I would have had smoke, and lots of it.

The clock it toast, but I have a spare to get re-worked for negative earth.
The aftermarket radio would smoke on positive earthing.
Fuel pump, see previous.

Could you tell from the battery cables?
Nope, as they had been tightened for negative earthing.
 
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