Totally Confused

[hicrop10]

As many of you know I’m restoring my B87,which has been in the family since new.I was always under the assumption it was positive ground being it was built in 1964.My electrician friend tells me it’s negative ground,he had a test gauge that says so.My question is how do I check to verify what it is?The truck has a voltage regulator and a generator,generator is not working so I’m getting that fixed.

[Geoff Weeks]

1st look at the generator regulator, sometimes they are marked as to polarity.

2nd does the truck have a working ammeter? If so hook up the batteries and turn on all the lights, wiper, heater etc and see which way the ammeter needle moves. If it moves toward the + side of the ammeter you have the wrong side of the batteries going to ground, if it moves toward the - side, you have the correct side grounded.

 

There is very little to do to switch from one polarity to the other on the old generator system trucks. Everything will function just fine on the reverse polarity with the exception of some electric gauges, most will read correctly but some types will read backwards. Of course any modern radios will be damaged with the wrong polarity. Alternators will be damaged, but not generators.

Once you have determined which polarity, all you need to do is "polarize" the generator. This is most easily done at the regulator. With the engine off, jump momentarily from the "bat" terminal to the "A" or gen (not the F or field) terminal to establish the magnetism in the field poles shoes of the generator. That is it!

If you still can figure out what it was from the get go, choose one polarity (I would suggest neg ground as it will make any accessories easier) and set it up for that polarity.   

[mowerman]

lol I’m no help… but  its hard to tell anything when you got everything stripped out good luck

[hicrop10]

7 hours ago, Geoff Weeks said:

1st look at the generator regulator, sometimes they are marked as to polarity.

2nd does the truck have a working ammeter? If so hook up the batteries and turn on all the lights, wiper, heater etc and see which way the ammeter needle moves. If it moves toward the + side of the ammeter you have the wrong side of the batteries going to ground, if it moves toward the - side, you have the correct side grounded.

 

There is very little to do to switch from one polarity to the other on the old generator system trucks. Everything will function just fine on the reverse polarity with the exception of some electric gauges, most will read correctly but some types will read backwards. Of course any modern radios will be damaged with the wrong polarity. Alternators will be damaged, but not generators.

Once you have determined which polarity, all you need to do is "polarize" the generator. This is most easily done at the regulator. With the engine off, jump momentarily from the "bat" terminal to the "A" or gen (not the F or field) terminal to establish the magnetism in the field poles shoes of the generator. That is it!

If you still can figure out what it was from the get go, choose one polarity (I would suggest neg ground as it will make any accessories easier) and set it up for that polarity.   

1st-the voltage regulator is marked mp,the fellow that I have dealt with the past 50 years tell me that mp stand multiple polarities (positive or negative).The generator is not working so he’s going to try and find parts to rebuild it.I don’t have anything else wired up yet.

[Geoff Weeks]

Can't say I've seen "MP" on the regulator, but that doesn't matter. Regulator (even those that are marked for polarity) will function fine on either. It was just the point material was place on the points that were optimized for one polarity. It made them last longer in the days where generator and point (mechanical) regulators were common.

 Now it doesn't pay to make and stock two regulators for every application. They make one, and figure it will last long enough. So little call for mechanical regulators these days. It has been like that for 30 years or more.

I have two trucks from the 40's and both regulators are still going strong. One I'm sure is the original, the other may be or may have been replaced at some point. 

 

If you have the truck wiring stripped out and are starting from scratch, then I would wire neg ground until I found something that didn't work right (gauge). then decide if it is better to replace that with a neg ground unit or switch to positive ground. 

[mowerman]

I was thinking the same thing…. I really can’t add much here … bob

[Vladislav]

5 hours ago, Geoff Weeks said:

Can't say I've seen "MP" on the regulator, but that doesn't matter. Regulator (even those that are marked for polarity) will function fine on either. It was just the point material was place on the points that were optimized for one polarity. It made them last longer in the days where generator and point (mechanical) regulators were common.

 Now it doesn't pay to make and stock two regulators for every application. They make one, and figure it will last long enough. So little call for mechanical regulators these days. It has been like that for 30 years or more.

I have two trucks from the 40's and both regulators are still going strong. One I'm sure is the original, the other may be or may have been replaced at some point. 

 

If you have the truck wiring stripped out and are starting from scratch, then I would wire neg ground until I found something that didn't work right (gauge). then decide if it is better to replace that with a neg ground unit or switch to positive ground. 

Geoff, how about the starter? I also have two trucks from the 40's. And a battery was once put wrong on one of them by my guy. To my great surprize the truck started (gas engine) and drove a few hundred meters to my shop. And I found out the mistake on the next day.

But the other one is diesel. And when I tried to apply different polarity to the cranking motor while its rebuild (reassembly) it spinned oppositely.

[Geoff Weeks]

9 minutes ago, Vladislav said:

GAnd when I tried to apply different polarity to the cranking motor while its rebuild (reassembly) it spinned oppositely.

older direct drive starter will spin the same direct on either polarity (as you found out). PMGR (permanent magnet gear reduction) starter will spin backwards on reverse polarity. 

To reverse direction on a wound field motor, you need to reverse the current in the field relative to the current in the armature. If you reverse both, they still spin the same way. With permanent magnets for the field, they will stay the way they were magnetized when the motor was made, and by reversing the flow through the armature, you have reversed the armature relative to the field, and vola, it spins the opposite direction.