12 volt Chevy Alternator - Is it charging?

[Fastfrankie]

I bought a M715 that has both 24 volt and 12 volt systems. It has the older style Chevy alternator (maybe mid-late 1970's-early 1980's) and has one wire coming off the positive post.

Seems that every two months, the 12 volt battery is weak/dead and I have to charge it overnight. Once I put it back in, everything is fine again - my lights work etc.

I am curious if the fire department wired the alternator in correctly and even if the alternator is even working at all. Any ideas on how to check this alternator out and even if it is charging the battery?

I am getting a strong feeling that it isn't working at all and that is why the battery is being drained through using the lights and then it just winds up being discharged.

I thought about buying a cheap 12 volt amp gauge and mounting it to see if the battery is being charged...

Suggestions and things to look for would be great. Any way to spot check just the alternator itself?

[adk4x4]

Test the voltage across the battery before and after starting the truck. If the voltage stays the same or is less then you've got nothing.