hey guys, i thought my slow starting problem was coming from a weak starter until i replaced one of my batteries with a new fully charged one. aft i did that it was starting fast and really well for about 2 days. after that it started getting weaker and weaker. i took the alternator off to get tested and noticed the one i have is a 100amp when the truck originally came with a 60 or 70 amp. the alternator tested good. so my guess would be the voltage regulator but could the 100 amp alternator be causing problems? the batteries do charge while the engine is running just not enough to turn the motor over as fast as it should unless i put the batteries on a charger.

 

I do not see a problem with the higher output alternator if the regulator is doing its job. What are the volts going to battery at idle? If they are low, look at the wire from the alternator to the battery. It may not be a sufficient gauge or has corrosion. This would limit the output to the battery.

 

You should not change just one battery at a time. If the other battery is no good or weak, it will pull down and hold your newer battery back and it will not perform very well either.

Like the other poster said, what is the battery voltage with the truck off, and with the truck running?

 

I do not have a voltage meter but I can get one tomorrow. Where would I put it to test? I'm looking at the wires now and they look like a jumbled mess. Some look to have been replaced but it's not pretty. Is there a company that sells a harness kit for it? Or a diagram that could show me how to make my own?

When I had bought it the po replaced one of the batteries. So now I have two new ones

 

Upon further investigation I did find on the regulator there's 4 plugs labeled I A S F and the I had no wire attached. Am I missing something there?

 

That depends on whether you have a cluster with idiot lights or gauges with an ammeter.

There are two ways the regulator is wired.

Is the regulator properly grounded?

 

Just put the meter on the battery. With the truck off you should have a reading somewhere around 12v. With the truck running, if it's charging you will have something higher, 13.5v or higher.

 

On a 6.2 diesel (yes GM) I had, when I changed out the bad ALT little did I know the pulleys were a different size so at idle the ALT did not put out the volts the old one did before it went belly up.


By the time I found this the old ALT was gone for a core so I lived with it. Never had low batt. but would see it on the volt gauge.
Dave ----

 

An the alternator I have 13.6 at the batteries I have 12.4 with engine in or off

 

Check the large (charge) wire for continuity between the alternator post and the fender relay stud.

There must be an open or very high resistance there.

 

Replaced the voltage regulator and suddenly the batteries started charging. They read 12v when the engine is shut off and 14v when running