Dumb question...how to tell if my 48 M is + or - ground?

R Weld

Member
I'm getting ready to buy an electronic ignition for my 48 M. I need to know if it is positive or negative ground. It has been converted to 12 volt if that matters
I'm an old car guy...I thought everything else was negative ground. Thanks
 
Alternator or generator??? If an alternator it stands about a 99% chance it is - ground. If you are an old car guy you should be able to tell if it is an alternator or not. By the way if is has an alternator on it and you hooked it up wrong the alternator will smoke so fast you can not pull the cable back off fast enough
 
positive ground = battery cable of positive post is bolted to the tractor on the other end for ground. Negative cable is hooked to power point. Negative ground = just the opposite. Negative cable bolted to tractor as ground. Positive cable goes to power point.
 
The 48 M was originally positive ground 6 volt. With the 12 volt conversion, its anyones guese what you got. Inspecting where the battery cables go should tell the story. Unless, UNLESS some idiot hooked battery up backwards since the conversion. Negative ground should be just that. Negative cable hooked up as ground. Postitive ground, the positive cable should be hooked up as ground.
 
Well, if you want to do it with a digital multi-meter, place the (+) red test lead on the starter post and the (-) black test lead on the tractor frame.

If negative ground the voltage will display as positive voltage. (the net effect is the red lead is connected to the battery + post [thru the cable] and the black to the - post [thru the tractor frame])

If it is displaying negative, the ground is positive. (the net effect is the red lead is connected to the battery - post and the black connected to the +)

Clear as mud, right?
 
Your M was originally 6 volt positive ground. 12 Volt negative ground has been around for almost 60 years now. Most all alternators are 12 volt negative ground. Most components except an alternator and an electronic ignition can be converted to either ground. On a 68 year old tractor the best answer might be: what would you like it to be, and then build it to be that way.
 
Assuming that your ignition wiring is intact, if the wire connecting the coil to the distributor is attached to the negative terminal of the coil, then it is a negative ground tractor. Vice versa applies.
 
(quoted from post at 01:25:59 09/11/14) Your M was originally 6 volt positive ground. 12 Volt negative ground has been around for almost 60 years now. Most all alternators are 12 volt negative ground. Most components except an alternator and an electronic ignition can be converted to either ground. On a 68 year old tractor the best answer might be: what would you like it to be, and then build it to be that way.

The Delco 10SI alternator can be built for positive ground also if desired.
 

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