[cade_dutt_12v]

Hello all,

‘I have an issue that I have been trying to fix on my 1998 12v. I have read through all related forums with the same topic with no luck. I will start off with symptoms and backstory.

Manuel swapped 1998 dodge 12v Cummins. I mention that because I know from reading that the voltage regulator control in the PCM is somewhat related to auto trans wiring. ( I did this swap about 5 years ago and no issues until now, just wound up and zip tied above Manuel trans.

what I believe to be the original alternator, went out on the way to a desert trip. And lights starting dimming more and more until the batteries fully died and just kept the truck running until I arrrived, to look into it while I was there.
Confirmed alternator was dead and not charging, bought a high output XDP alternator, installed along with new batteries since I drained them so badly.
Now the truck is still not charging, and had a fried who is better at electrical help troubleshoot and test as much as we could with the help and suggestions from other posts. And have found that the blue wire from the PCM is not giving the alternator any power to charge.

I have followed the blue wire and did not find any damage or shorts,. I was ready to try and buy a PCM but am also reading that it is generally never the PCM, and that they are so likely to go out.

any other recommendations or experience with this that I should look into beforebuying and trying a PCM.
Lastly, I bought a cheap external regulator, but the more I read, the more I would like to try to have it working properly instead of more of a band aid.

thank you so much and anything is appreciated.

 

[cade_dutt_12v]

Sorry, few more details I would like to add. That was about the same timing.

my entire instrument cluster was crazy for about a year. I didn’t drive the truck much so didn’t bother me too much. It got too the point wherenothing worked and was doing some routine maintenance while doing the alternator. While doing that and replacing with a new belt I found my crank position sensor wires cut from the belt. So all my gauges were fixed. Doubt that could short the pcm but thought I’d mention

 

[24hrsparkey]

Being a 98 12v , that dash cluster and PCM are rare / special.

My son has one.

Sometimes the PCM just stops controlling the charge / alternator . ( all years ) .
BUT i think further troubleshooting is ness , before condemning the PCM and sending it off to a fixer.

 

[jimduchek]

Just to clarify, all your gauges work correctly, and your only problem is that the alternator will not charge? If that is the case, I agree it's highly unlikely (though not impossible) to be the PCM -- they tend to die outright, not just one part of it, which means your gauges wouldn't be working. If the tach is working then the PCM knows the engine is running. Any codes if you plug it in?

 

[Down Under Dually]

Being a 98 12v , that dash cluster and PCM are rare / special.

My son has one.

Sometimes the PCM just stops controlling the charge / alternator . ( all years ) .
BUT i think further troubleshooting is ness , before condemning the PCM and sending it off to a fixer.

Hey mate, do you mind elaborating a bit on the rare/ special nature of the '98 dash and PCM please? My truck (well the cab at least) is a '96 however I am 99% certain that at some point in it's life its had a '98 wiring loom, dash etc installed into it. I don't have any other Second Gens around here to compare to as they were never a factory import, so I've been groping in the dark a bit in the past few years.

Sorry for the thread hijack

Cheers

Joel

 

[smokinu2]

Hey mate, do you mind elaborating a bit on the rare/ special nature of the '98 dash and PCM please? My truck (well the cab at least) is a '96 however I am 99% certain that at some point in it's life its had a '98 wiring loom, dash etc installed into it. I don't have any other Second Gens around here to compare to as they were never a factory import, so I've been groping in the dark a bit in the past few years.

Sorry for the thread hijack

Cheers

Joel

1998 was a transition year for the 2nd gen ram both in terms of powerplant and interior. This is common for any generation of vehicle and is often referred to as a mid-cycle refresh. The switch form 12V to 24V powerplant was emissions related though. The timing was less than ideal and we all wish the 12V would have stuck around a few more years.

Consequently, the 98 Ram has parts on it that are unique to that year only. Further complicating it, there are 1998.4 parts and 1998.5 parts that do not interchange with each other. Like stated above, if you need a PCM for a 98 12V, you're looking for something that was only manufactured for six months. Hen's teeth...........

 

[jimduchek]

Hey mate, do you mind elaborating a bit on the rare/ special nature of the '98 dash and PCM please?

The 94-97 instrument cluster gauges attach directly to the sensors they represent. Only the tachometer is fed by the PCM (though the PCM also supplies 5V to the vehicle speed sensor, so a dead PCM can kill the speedo too).
The 98 instrument cluster is entirely computerized. The sensors are read by the PCM, which tells the instrument cluster via a digital bus what to display on all the gauges.
So while some parts on a 98 12V are common (the instrument cluster itself, for example, is shared between all 98-02 Rams), some parts (like, the PCM or the engine harness) are very, very specific to 98 12Vs.
See attached -- the instrument cluster with the wood background is a 94-97, the one with a white background is a 98.

 

[smokinu2]

The 94-97 instrument cluster gauges attach directly to the sensors they represent. Only the tachometer is fed by the PCM (though the PCM also supplies 5V to the vehicle speed sensor, so a dead PCM can kill the speedo too).
The 98 instrument cluster is entirely computerized. The sensors are read by the PCM, which tells the instrument cluster via a digital bus what to display on all the gauges.
So while some parts on a 98 12V are common (the instrument cluster itself, for example, is shared between all 98-02 Rams), some parts (like, the PCM or the engine harness) are very, very specific to 98 12Vs.
See attached -- the instrument cluster with the wood background is a 94-97, the one with a white background is a 98.

The 98.4 12V cluster is different from the 98.5-02 24V cluster. The tach has a higher redline on the 24V, and the odometer window/display is different. It's possible they are interchangeable though.

 

[cade_dutt_12v]

Just to clarify, all your gauges work correctly, and your only problem is that the alternator will not charge? If that is the case, I agree it's highly unlikely (though not impossible) to be the PCM -- they tend to die outright, not just one part of it, which means your gauges wouldn't be working. If the tach is working then the PCM knows the engine is running. Any codes if you plug it in?

Correct, all of my gauges work as they should. Sorry for the late reply.

I ended up needing to use the truck and installed the external voltage regulator, though would still like to r some point figure out how to fix the actual issue. It does charge higher than I was used to. 14.8 volts idle and nearly the same with throttle. Haven’t seen it above 14.9with a meter to the battery.

I will have to check codes again as I don’t remember what they were. I am pretty certain the were all pertaining to auto trans, which those have all been there since the swap with no checkengine light.