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texas_outlaw

Electrical problems

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Truck is a 97 2500 4x4, swapped in a nv4500, retained the auto PCM and grounded NSS wire. Speedo did not work on the initial road test, shut the truck down at the house and an hour later we took the truck on another road test and everything was working normal. After two days of driving normally I parked the truck in the driveway, came back out 30 min later and when I keyed on there was only oil and air bag light prove out. No engine, gen, wts, trans temp or wif lights come on during initial key on for prove out. A/C is not working, alt. not charging and tach is dead. All other gauges work properly and read normal. I have replaced the ESS and gapped at 0.050", all fuses in the cab and under hood have been checked with test light and dvom and all are good. Battery connections removed and cleaned, grounds all seem to be making good contact and power is present on other side of fusable links. When the problem first started I removed the 20amp fuel system fuse under the hood with the engine running and the alt. started charging(overcharging after a min or two) and a/c compressor stayed on no matter what position the selector in the cab was at. We pulled the harness this weekend to inspect and found no issues. I found a connector pinout for the pcm connectors but the circuits are hit and miss with whats on my truck. I have no diagram to follow but, as far as i can tell my constant and switched 12v are present at the pcm as well as the grounds. I can ground the individual circuits for the wif, eng., gen ect. and the lights illuminate in the instrument cluster. Sorry for the book but any help is very much appreciated.

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I don't know anyone with a 97 that would swap. Do yo know of any reputable places to get a PCM? On the verge of putting external regulator, different tach and wiring compressor to a switch!

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I wonder if there's more to this. I mean it ran fine before I assume and now something is tripping the PCM up. Do you have wiring diagrams and stuff to double check things you may have brushed up against? You can get them in the downloads section.

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I dont have any diagrams to follow and was unaware of the one in the downloads section. Thank you for pointing me to that. I will have to wait until Friday to get back to working on the truck, raining today and trick or treat for the kiddos tomorrow night. It worked fine before the swap and for two days after the swap. Just happened out of no where and caught me off guard....the wife swears its something I did. Thank you for the help!

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If you track everything down and multimeter everything and cant find any shorts or anything, let me know and I can send you my PCM. It's a 1997 5spd, have to check with someone else to see if it would work.

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Since nothing with the PCM seems to be working how does the ground for the PCM check out? I believe it grounds out on the front of the engine either by the intake or thermostat housing.

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Since nothing with the PCM seems to be working how does the ground for the PCM check out? I believe it grounds out on the front of the engine either by the intake or thermostat housing.

I really don't think I can help much..... but on my 02 the PCM ground goes to the firewall, just a short distance toward the driver side. There is another ground from PCM to the passenger battery, negative post. Check the factory connector in that wire. Some have chased away a problem by getting rid of the connector and soldering the wires together. I'm getting a little older and I accidently crossed wires and put full battery power thru all the grounding system. Truck thru codes and did strange things..... not shifting... temp gauge very high.... CEL was on all the time. I cannot remember all the codes nor every symptom but after disconnecting batteries for an hour or so everything worked properly on the truck after that. Had to have codes cleared and did not come back. I was very lucky my PCM and ECM weren't fried. Sometimes you'll find an alternator that isn't fully grounded thru the mounting bracket, with some resistance there. I ran a seperate ground wire off the alt. Just throwing thoughts, not parts, if it helps........... I do think the electrical system on our trucks is very sensative so therefore can easily be effected by any wiring anywhere on the truck that may not be in number one condition.
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Thank you for the recommendations. I had a buddy I haven't seen in a year call me last night and started talking about trucks. He just bought a 97 3500 and said he would be more than willing to swap PCMs to help if wiring is not my issues. Come friday I will be burried in the diagram and truck harness.Sent from my SAMSUNG-SGH-I747 using Tapatalk

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The auto and manual PCMs should be the same, and I also believe that 96 and 97 are the same, 95-94 have a different plug setup.I got a 96 5spd CTD and a 97 auto V10 I'm going to swap the PCM here soon just for grins, Just got to get the 96 back together enough first lol. I had a problem like this where only half my guages worked and it wouldn't charge, problem was the mother-of-all-plugs under the dash that goes through the firewall has a bolt to hold it together. Well I missed tightening it all up so it wasn't plugged in all the way.

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Got home late today and didn't get a chance to check the truck out. Was notified today I have to work all day tomorrow but, I will also be able to swap PCMs with my friend just to rule it out. Part of me hopes its the pcm so this whole ordeal will be over and the other part hopes not so I don't have to spend $400-$500.Sent from my SAMSUNG-SGH-I747 using Tapatalk

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PCM it is!!!!!! Now are there any suggested places to get one? Is cardone worth a damn? Thank you everyone for your help.Sent from my SAMSUNG-SGH-I747 using Tapatalk

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Ended up buying a used one from a manual truck in the for sale section here. Its been driving awesome for 4 days so far!! Thank you everyone for the help.Sent from my SAMSUNG-SGH-I747 using Tapatalk

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wish I'd caught this sooner...I would have said to try running an external voltage regulator, seeing as if the factory one goes bad (located in the PCM) it can often cause all the issues you had...

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