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Discussion Starter · #1 ·
NEWBIE NEEDS HELP
I am feeling a little embarrassed but here it goes. I bought a 94 Power Ram 2500 today owner said it needed a new alternator. With the old alternator in I did the test drive checked everything from soup to nuts it drove well and ran well. So I bought it.
Ran to the loca Napa mpicked up the alternator and changed it out in his driveway all looked ok, the battery level indicator in the cab looked a little low when I started it but I thought OK maybe the battery is weak(eternal optimist) Well I got 10 miles down the road and it started to chug and the charge indicator was reading 8 volts and when I hit the brakes it went to zero and the speedo went to zero. I got to a parking lot and shut it off. Now it will not start. Now I am thinking the battery might be bad as well. I am sure I hooked up the alternator correctly. So i bought a bettery on tthe way home and I am going back out there tomorrow to try the battery. Anyone have any ideas out there??? It all appeared good on the test drive with the fresh charged old battery but it does not work now??? HELP:doh:
 

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If the alt is bad it can damage the battery. If the battery is bad, it can likewise damage the alternator.

I'd remove them both and have them checked out. If they both come back with the green light and are okay, then there is the voltage regulator which is what I suspect your problem is.

That leaves you two options (three actually). Since the regulator is in the pcm you'll have to:
A.) Replace the pcm.
B.)Have the pcm rebuilt; or
3.)Install an external regulator.

The first thing is unhook all the original electrical connections from the alternator. Then take a wood chisel to the little black molded box and break it apart to reveal the individual ground and alternator output cables. Then, pull apart the wire loom that runs over the upper alternator mounting bracket that has the two wires connected to the original alternator field, and cut, heat shrink, and tape them. Re-install wire loom over those wires. (you're deleting them and just removing the ends) Now, the 2 little green and orange wires need the ends cut off, heat shrinked, and taped. The rest is easy, take the wire connected to the top post on your regulator and run that to the upper field connector. The 2nd wire down on the regulator goes to switched power, The final wire goes to the positive (ouput) wire on the alternator. Lastly, you need to ground the other (lower) field post. Loop a short wire from that post to the ground connector on the alternator case.



 

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If the ecm is bad, i go this way, napa reg #vr38 and conector #vrc38. There are two field wires, should be one blue and one green, blue wire is key hot tap into this wire with blue wire on vrc38. Cut the green wire then run the alt side to green wire on vrc38. This reg must be grounded.
 

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Discussion Starter · #4 ·
ECM or PCM are they the same.

I was able to get it home(New Battery) about a 45 minute drive but by the time I pulled into the driveway the battery was getting weak. The alternator is outputing 36volts. At the battery it is reading about 11.64 volts.
Now I am not sure but are we all referring to the ECM on the passenger side firewall. Because of all the posts I have been reading on this some are referring to a PCM and some ECM.
I see the regulator mod, and it looks quite easy to do and I am open to that, and it would get me running very quickly if this is the problem. But I guess the check engine light would stay on( a little annoying) The other option is 400.00 for a rebuilt computer.
Has anyone that done this mod run into any other problems.
 

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Discussion Starter · #5 ·
Got it home with new battery

If the alt is bad it can damage the battery. If the battery is bad, it can likewise damage the alternator.

I'd remove them both and have them checked out. If they both come back with the green light and are okay, then there is the voltage regulator which is what I suspect your problem is.

That leaves you two options (three actually). Since the regulator is in the pcm you'll have to:
A.) Replace the pcm.
B.)Have the pcm rebuilt; or
3.)Install an external regulator.

The first thing is unhook all the original electrical connections from the alternator. Then take a wood chisel to the little black molded box and break it apart to reveal the individual ground and alternator output cables. Then, pull apart the wire loom that runs over the upper alternator mounting bracket that has the two wires connected to the original alternator field, and cut, heat shrink, and tape them. Re-install wire loom over those wires. (you're deleting them and just removing the ends) Now, the 2 little green and orange wires need the ends cut off, heat shrinked, and taped. The rest is easy, take the wire connected to the top post on your regulator and run that to the upper field connector. The 2nd wire down on the regulator goes to switched power, The final wire goes to the positive (ouput) wire on the alternator. Lastly, you need to ground the other (lower) field post. Loop a short wire from that post to the ground connector on the alternator case.



Hi Warlock,
Thank you for the reply, I am trying to diagnose this further and this is what I have found. With engine running Alternator outputing 36 colts at the battery I have 11.64 volts. I did not check the current. Is it your experience that this indicates the ECM/PCM
 

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Discussion Starter · #7 ·
Well isnt this an interesting development

:SHOCKED:
the 140 amp alt fuse has blown. ecm/pcm same thing, yes it's on pass firewall. with the alt putting out 36 volts that shows it's working. the volts just can't get to the battery.
Guess what you were right 120amp Alternator fuse was blown. ???? I will get one tomorrow and try again. Thank you for the pointer. I thought it did not look right but had not yet checked that. :smileup:
 
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