Prostar alternator, replaced and still showing lower voltage

I definitely second that on checking the starter connections. my positive cable from the alternator failed at the starter because of their design decisions to connect a 4 gauge wire to 4 10 gauge wires into a terminal.

 

I am with the others who suspect a faulty ground issue, there should also be a ground strap from cab to frame. If you can get your hands on a wiring diagram it will show the ground points as well as the power supply circuit.

 

I have 2011 prostar and the battery VT going under 12 and lights came on, was at TA did battery check they said alternator not charging the batteries, now looking for alternator, any suggestions about aftermarket part? Cause OEM is 526$

 

On my 2008 ProStar I was having similar issues, everything stated above and more. I wound up replacing every bit of cabling that left the battery box, over 100 feet of it. To my horror, I discovered that from the factory, I had bare exposed copper on every one of my electrical cables that left that battery box including a few grounds to the frame. I pulled the main starter cable out, 10 inches of bare copper at the starter. That piece of cable was roughly 15 feet long, and was GREEN from end to end. My other battery cabling and grounds were in the same, if not quite as bad of condition.

That is where I would start. If the cabling is bad, which I suspect it is, I used copper welding cable from a local truck repair parts house. I brought in the old cabling, he matched it up and installed the ends for me at no charge. They had one of those cable end tools that properly crimped on the electrical connectors. Since doing that, electrical gremlins are gone.

Also, on your alternator, check your build sheet to see which alternator your truck came from the factory with. On the ProStar, there were two differnet amperage models used. One was around 185 amps and the other was up around 300 amps. If you have a truck that came with one of these higher amp alternators and are using the lower amp version, this to will cause some of the symptoms you describe, and could possibly damage the ECM and BCM. Just something to look in to.

 

Did you ever find out what the problem was?

 

My truck started doing the same thing this past Friday! So aggravating! Did you find out the issue?