Packard Forum Index » Post-War (1946-54)

We were on the subject of generator polarity in class today, and it got me thinking... The previous owner changed my car to negative ground, and said they had the gen and starter rebuilt. The car seems to run fine, but as long as I've owned it I've suffered bad voltage loss. Usually I have to charge the battery every other day that it is driven. The more I drive, the more often it dies. I was told that the generator polarity needs to be changed when the (+) to (-) ground swap is made. When i test my gen, how will I know if it was done? Will it just not work if the polarity is wrong?

Sounds like the beast isn't charging at all--that's why the more you drive the sooner its dead. Put a voltmeter across the battery terminals and you should get 6.8 to 7.2 volts at high idle.

Generators do need to be polarized when anything is changed. If your car is negative ground and you want to keep it that way, then take a jumper lead from the positive post of the battery and touch it briefly to the armature post on the generator (the one with the thicker wire).

If that's the real problem, you should now be good to go as the electrons will now march in the right direction when the engine is running.

If still no charge, look very carefully at what is stamped on the flanges of your voltage regulator. If it says 6 pos or 6P you will need to run positive ground or it will not be happy if it isn't ruined already.

Here's the easiest test in the world to see if the generator itself is OK: Take off the fanbelt. With one jumper ground the field terminal (small wire)to anything convenient. With another jumper now apply battery to the armature terminal. The generator should now run smoothly as an electric motor. If it won't then it needs to be serviced.

Ahhhh! So these are positive ground? is the 49?

Quote:

Yes,it is. Up until 1954 for 6 volt systems and 1955 for 12 volt.

thought it may be, my 48 ford was.

Somewhere around here I have an old reference, but I can't find it. I found my ancient picture of the late Earl Heath without his costume quality toupee and the Greta Garbo Duesenberg.

Anyway from memory it's something like this:

All 6 volt cars positive ground except:

Buick
Chevrolet
1937 Cadillac and LaSalle only
K series Lincoln, Linclon Continental (Lincoln Zephyr is positive ground)
Oldsmobile
Willys

If I ever find it I will audit this list.

I thought ALL GM cars were negative ground??
For sure Cadillac was from 49 up. Pontiac also.

So, I tried testing the gen today in school.... It puts out zero power, and failed the motoring test. So now I am in the search for another gen!! Am I correct in assuming that any Delco 6v genny will work? My shop teacher's dad as a pretty big collection of old parts, specifically 40s era Chevy stuff. He has a sweet '41 Chevy coupe that's still 6v, and has a 216 all hopped up with period parts like an Edmunds 2x2 intake and Fenton split exhaust....

Just because it doesn't have any output doesn't mean you replace it. Determine what's wrong with it - chances are it can be returned to service easily.

Not just any. You're going to want one with sufficient amps out and to match your regulator. 45amp generator is listed for 52. Some earlier and other make cars using Delcos are as low as 25-30amps. Have you looked into what it would take to be repaired. Unless you have a large selection of known good ones to choose from for free, it might be more cost effective to have yours repaired.