The Stovebolt Site Forums The Shop Area The Electrical Bay Positive ground vs negative ground

My 41 has been called into active parade duty this year. Talk about fun!

Last week, despite being 100 degrees, everything went fine. Today I went to the garage, hit the starter and got a whole lot of nothing. I swapped out a 12 volt and did the parade. The 14 month old 6 volt battery tested bad and has been replaced along with the terminals on the wires, so the future looks brighter. I've never had any battery issues before today.

As I did all of this today, I noticed it was hooked up as positive ground. I thought Chevy's were always negative ground. Am I wrong? Are there any longevity issues/benefits to one over the other?

I switched them around to be more what I expected, but now when I drive, the amp gauge reads a heavy discharge. Do I need to flip the wires around on the generator when I change the rest of the system, and what else do I need to change?

Thanks!

Jake

jake53,

I am not sure I understand what you are saying, or asking. It sounds like you swapped a 12 volt battery for a 6 volt...unless you did a whole bunch more your parade days are numbered.

To my knowledge your truck would have been NEG ground. The ammeter is polarity sensitive, so if the system is actually operating correctly, the leads on the back of a ammeter gauge would be swapped in order to get it to read properly.

I am guessing you have left out a lot of what you have done in your explanation above!


Stuart

Jake - you need to polarize the gen/reg for starters, and as Stuart points out, you may have fried some of yer gauges, at least fuel, by using 12V even for a few minutes

Bill

To do the parade, I just swapped the 12 volt for the dead 6 volt. After I got a new 6 volt, I reversed the polarity of the system to negative ground. I know I may have cooked the fuel tank sender or gauge, but it seems okay.

My concern now is that when I rev the engine, the amp meeter goes way negative. Is the amp meter wired backwards and needs to be fliped, or do I need to switch the wires on the generator?

Jake53,

I am actually surprised you made it through the parade without fizzling out...sticking a 12 volt battery into the 6 volt truck and taking it for a spin is unorthodox to say the least.

Do not switch wires on the generator, this has no bearing on your amp gauge.

As I understand it now, you have the 6 volt battery installed, and the negative terminal is attached to the appropriate spot.

Before I did anything else, I would take a volt meter and verify that the generator is actually putting a charge into the battery.

I am not really clear on the pos/neg deal, but the regulator in the charging system could have been damaged as polarity was changed and improper batteries were installed.

So...put the system back to stock..6 volt negative ground. Check the charging system for proper output. If everything looks good, the ammeter might have been switched previously to accommodate the positive ground. The wires on the terminals could be swapped back to reflect the negative ground.

Depending on how long you ran the truck with the 12 volt battery, other components could have taken a hit...this will be revealed.

Stuart

What's the best way to check the output?

I'm thinking the wires to the ampmeter were switched, but I want to be as sure as I can. The last thing I want is to die in the middle of a parade in two weeks.

The strong discharge on the gauge spooks me.

My past experience is that these systems are more tough than we give them credit. My 53 was converted before I got it. Probably not done real well, but it has held up. I'll get this one back in order too.

Thanks for your help!

Jake53,

I always recommend buying a inexpensive VOM meter from your local hardware store. This meter will read AC/DC volts, resistance, and other values, depending on the meter.

Read the battery voltage with the rig off..then start the truck and bring the RPM up gradually. You should see the voltage climb to about 7.5 volts if everything is working. You will want to see a difference between voltage with the rig off and voltage with the truck running at a mid RPM.

You can do a rough test at night...start the truck, turn the light on, and as you bring the RPM up, your lights should get somewhat brighter. This will at least tell you that your GEN is GEN-ING!

When you start the truck, look at the ammeter at an idle. It will probably be centered...rev the engine up..if it swings over to discharge , it probably is as you have surmised..connected
backwards (to your new polarity) and is actually charging.

These are tough systems. Substituting a 12 volt for a 6 volt is truly a test of this system.

Maybe a old GMC fellow was the previous owner of the truck, and got confused when he installed a new battery..it sounds like you have a parade deadline, so grab a meter and cross your fingers!

Stuart

I'll try that today. I used the meter yesterday to learn that the battery was toast. Now I'll try it again and see what it looks like running.

Your guess is about the same as mine on how it got messed up. The red wire went to the engine ground, the black to the starter.

Should I just put it back that way and leave well enough alone? Everything seemed to work ok until the battery went dead... 14 months of light use seems like a short life. It just dropped dead.

I did notice that the heater worked (switch was bumped when opening the floor vent) when 12 volt was in use. It never worked 6 volt. Maybe same guy was confused and began a 12 volt rebuild when he re did the truck. The horn would just go "thud" when you hit it in 6 volt. I thought it was dead and removed it, so I didn't test it with 12.

I don't think he did a full 12 volt, because the battery always held a charge... Wait, maybe there is something to look at there.

How do I best test the generator/regulator to see what it is putting out? Is that best done at the battery too?

Thanks a ton! I think I'm getting there...

Here are the readings:

Cold - battery alone - 6.5volts
Started, low idle - 7.3 volts
Fast idle, mid rpm running - 8.8 to 8.9 volts
After running, battery alone - 6.8 to 6.9 volts.

While running, the amp meter shows a discharge, the higher the charge the bigger as you would expect.

Any thoughts?

Jake53,

The system is charging, although it looks like the max voltage is higher than it should be. As I recall, it should cutout around 7.4-7.6 volts.

The ammeter is a pretty dumb instrument, it is only showing you current flow through it, and I would say it is obvious that it is connected backwards.

The tests you performed show that the generator is functioning, and that the regulator is "regulating", just a bit high.

Your meter could tell you state of charge of your "toasted" battery, but wouldn't indicate if it were any good or not.

If you installed a new 6 volt battery, you want to make sure the system isn't going to overcharge it. If the battery compartment was full of acid stains, or the old battery was out of water and wet on top, this might be an indication your system has been overcharging for some time.

The regulator is made to be adjustable. Usually this is done by someone well versed in the procedure...no nose ring or pink hair!

The alternative to adjusting is to replace.

You might want to take a look at the Tech-Tip section. I think there is a good article on the 6 volt charging system compliments of Hot Rod Lincoln.

I guess you have made sure your battery connections were based on the positive and negative notations on the battery case and not solely on the color of the cables.


Stuart

I may read up on the regulator adjustment, or try a spare I have. If that works, I'm on my way.

The old battery showed no physical or performance indicators of being over charged. It just died. I don't get it. The meter never read a huge charge (unless the starter ran it down) before I did what I did yesterday. I don't think I cooked it.

I'll try another regulator and see what happens. I can't really explain what I did when I installed the new one last summer. I probably put it in the old battery was, since we were in a hurry to load and run, I must have not noticed the difference.

Now I'm looking and thinking, so I want everything as right as I can. Don't want to buy a new battery every summer...

Jake53,

Without a hydrometer and a load tester, troubleshooting a battery is tough. They are a consumable..usually four years of life and they croak.

You seem to have a real good mechanical sense, carry on and you will figure it out.

My only concern would be the amount of charge..it seems quite high to me. If you have a spare, it would be fun to try and adjust the one on the rig now.

Enjoyment is the name of the game with these old trucks.

Stuart

Okay, swaped the regulator with one from my part truck. Voltage now is a steady 6.35 volts. I'm guessing that one is dead, whereas the other is cooked to allow the higher voltage.

Time to order a new regulator...

Thanks everybody!

Any more thoughts are greatly appreciated.

regulator = regulate to voltage needed by the battery - if it's fully charged it doesn't need more than 6.35

have you polarized the generator anywhere thru this adventure? try it, you'll like it

Bill

Read this before you spend money on a new regulator you may not need.

Just a final follow up here.

I did buy a new regulator from Jim Carter. Priced my local NAPA, but they wanted twice as much.

With the new regulator, all is well. At full run, it will kick out about 7.35 volts, at rest it stays about 6.5. By the way, the gas gauge is fine!!! I was really scared about that one, but no real harm done. I'd still not recommend trying something so dumb without desperation.

Thanks again everyone!

red is right you will have to polorize the generator.