Positive To Negative Ground Conversion

[dmckeehan]

Recently acquired an 1966 C-95 open cab Mack fire truck. This truck has the thermodyne gas engine. Looking to convert it from a 12 volt postive ground system to a negative ground system. It does have the big alternator with AC output as well.

I've been doing some reading in a factory service manual for the truck and it appears that it should not be too hard to convert. What i'm not sure about is the alternator. Will the alternator charge correctly as a negative ground system? Will I need to change the leads on the coils around to optimize the performance as a negative ground? Any help would be appreciated.

[Firemack]

Here is link that explains how to convert the Positive to negative ground for both alternators and generators.

http://mgaguru.com/mgtech/electric/ac101.htm

Pretty easy.

Firemack

[dmckeehan]

Here is link that explains how to convert the Positive to negative ground for both alternators and generators.

http://mgaguru.com/mgtech/electric/ac101.htm

Pretty easy.

Firemack

Thanks Firemack. That helps. One question though. I've been told that an alternator could not easily be converted over to negative ground. I'm pretty mechanically inclined and have a good understanding of the negative ground systems, but never worked with a positive ground system. I'm not seeing why the alternator would have problems with the type of ground system. any insight into this? also, will the regulator have problems as it says on it that it is for a postive ground system?

Edited October 24, 2007 by Daniel McKeehan

[Firemack]

Dan,

If you read through the section about installing an alternator in a postive ground system it also discusses changing the charging wires to the voltage regulator. If the alternator was already used in postive ground system you may need to polarize the alternator- however if it has not been used in a positive ground system you should be able to bolt it in and wire it up.

The voltage regulator can be either postive or negative ground. Either way works. The important item is to make sure the charging circuit is wired correctly per the instructions.

If you are using the generator it will need to be polararized for the negative ground and utlize the same voltage regualtor etc.

Firemack

[dmckeehan]

Dan,

If you read through the section about installing an alternator in a postive ground system it also discusses changing the charging wires to the voltage regulator. If the alternator was already used in postive ground system you may need to polarize the alternator- however if it has not been used in a positive ground system you should be able to bolt it in and wire it up.

The voltage regulator can be either postive or negative ground. Either way works. The important item is to make sure the charging circuit is wired correctly per the instructions.

If you are using the generator it will need to be polararized for the negative ground and utlize the same voltage regualtor etc.

Firemack

Thanks again Firemack. I'll reread the pages and do some cipherin. You've been a big help.

[Greg Rider]

The alternater that is in my A-30 has 4 studs on the back, a"+", "-" and two that are marked "AC".When I had it checked out the told me it has an isolated ground and can be wired in either direction.Read up on my posts in the electrical section also.Speed was working on converting to neg.ground system.It is more time consuming than difficult in my opinion.