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96 Ram 2500 multiple issues

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Recently given a 1996 Ram 2500 12 valve 2wd automatic. Its got a few problems with it: 


Its in limp mode. 3rd only unless you manually shift. No tach. No speedo. No wait to start indicator.  I assume no grid heaters are working because the truck doesnt feel like its cycling them when its cold enough for it. Voltage runs a bit high. Like 15-16.5 volts and it fluctuates in that range. Lights follow voltage fluctuations. It has an external voltage regulator so at some point it has had PCM related charging issues. No MIL. OBD ii doesnt want to work but it may be directly related to the fact that my scan tool is a 25 dollar special from a local autoparts place. Once in a while the tach will flick up to a few hundred rpms when you start it but it drops back to 0 within a quarter of a second-ish. ASD relay is missing and has been jumpered. 


Unless im mistaken the ESS needs 5v reference? I cant remember what it was when i checked at its connection but i want to say it was less than 2v with key on. backprobing pins A4 (sensor gnd) and A17 (5v reference) gives me no voltage reading. Probing A32/A31 (its just listed as ground in the FSM) and A17 gives me 1.75v.  A22( fused battery) to A31/32 gives me 12v so i do have power to the PCM, correct? 


I haven't gotten any further than that due to time constraints and prior engagements so what I've verified stops there. 


Is it possible that the internal voltage regulator going bad caused the PCM to let out the magic smoke and my problems lie there? I need to replace engine/battery hot/grounds and that may alleviate my voltage fluctuations. How often do those bolt-on external regs go bad? 


 I've got the Service Manual printed out in its entirety and am currently trying to track down a powertrain diagnostics manual to boot, if there's one to be had. They're pricey on Ebay used for my budget.  


Any leads on other things to look for? Suggestions would be greatly appreciated. I have to get to bed soon so i may not respond for some hours but i will respond eventually. 


Thanks much. 



Edited by elijah123
added/clarified things

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