webbrenda

No they didn’t. I posted the last update a little too soon. After I got the alternator replaced, the first time I started it the WTS light came on almost immediately( maybe a second or two ) after key on and truck started right up. Thought I had it. But after putting everything else back together and finishing mounting fuel pressure gauge and boost gauge it does take a few seconds( 3-10) for the WTS and the LP doesn’t run with bump start. At one point after the the harness and ECM both worked the way they should. Getting a little lost on the sequence of events. Should I send the ECM in or do you have any other ideas what would cause it? Not sure why it worked at first several times but now it doesn’t.

Bad alternator off the shelf. Resolved and everything is back to normal. Damn what a process.

John. replaced the fuse after testing as you suggested. All is well. I’m only getting like 12.8 volts from alternator but I just ran the truck for a few minutes. I’ll drive it and let it get up to temp and check it again. I have no codes and truck runs well. The only odd thing now is the WTS start light is delayed a few seconds and it wasn’t that way earlier in this process. And the LP doesn’t run after bump start but it does come on for a second after the WTS and it runs after it starts and I’ve got 15psi. I can’t thank you enough for all your input and help with this.

Thanks again for your time and knowledge. I assumed after it blew the fuse it must have something to do with the harness but I checked the blue and black wires from alternator to corresponding pins on PCM and they are correct and show good continuity. Everything was pointing to voltage regulator in PCM I thought( before reading your response about current having nowhere to go) so I sent my boy to town for an external regulator and just got done wiring it in and still have 22 volts at alternator. I also assumed the high output was what caused the fuse to blow. Any ideas what would have caused it to blow? I replaced alternator earlier in this process because it was showing low voltage at the gauge and I was grasping at straws and it did test bad at O’Reillys. I have had the truck running off and on by jumping pins on the relay and can’t say for sure when the fuse blew. With the only thing in that circuit being the alternator and battery and if the high output didn’t cause it I’m lost as to why it blew. Just reread your response and I guess it is possible that I shorted it out when I had the PDC box up and out of there tracing wires. I am sure I am overthinking some things. Every time I find something and fix it something else rears its ugly head. Couldn’t find a fuse anywhere today but will have one tomorrow and I’ll replace and see what happens. Thanks again

I know I’m not going to have enough information but here goes. I found a blue wire and the brown/white wire in opposite positions of where they were in the old harness so I cut and spliced them to correspond to match original harness. Now I have voltage to relay and truck starts and runs fine. CEL went out and I have no codes. I thought I had it but noticed volt gauge was only showing 12 volts or less with new alternator. Checked the big wire at back of the alternator and it’s putting out around 22 volts and blew the 140 amp fuse. Checked the blue wire at back of the alternator and it’s shows 12 volts. What would cause the alternator to be putting out 22 volts? Voltage regulator correct? I’m not knowledgeable on how the regulator works in the PCM nor do I understand how anything with what I did would cause it. Help please and thank you.

Yes. Thank you. Looks like that part number for 1999 is the other end of the harness that connects to PDC. I was looking for the ECM harness. Would you happen to have those part numbers?

I was using a 99 wiring diagram that was posted on here. The brown/white from pin 36 goes to the 11 pin connector at the fire wall and straight to relay. I can’t find anything that shows those 11 and 14 pin connectors for a 99. I found one for a 2000 but I haven’t been able to figure out what harnesses interchange or if any of them do. From ones I’ve seen for sale it looks like the 98.5 and 99 were the same and 2000 and 2001 were the same. I can’t imagine why the new one I bought has all the correct plugs and all the wires on the ECM plug are correct but it is different at these two plugs.

I went through and all the wires on the ECM plug match color and position with the original. The issue is at the 2 plugs at the end of the harness that connect behind engine at the fire wall ( the 11 and 14 pin pin connectors). Short of completely undoing all the wrap and tracing each wire I’m not sure what to do. I do find that there is a solid blue where the brown/ white wire should be and the brown/ white wire is where the blue wire should be compared to origainal harness but there are extra wires on this harness compared to original. Can’t seem to find a diagram that shows color wire on the 11 and 14 pin connectors.

John I just ran a jumper wire from pin 36 which is a brown with white tracer and didn’t have voltage to pin 86 at the fuel system relay. In tracing the wire up I found that the brown/ white wire isn’t in the same location in the plug at the back of the engine at the fire wall. This is a new wiring harness I purchased from Firsttruckparts. Their part number is 3944847 but it says “ other oem part numbers and list 4 or 5 numbers. One of which is 3934387 which I thought was the one I needed from looking at several websites. All the connectors on this harness are correct and in the correct location. Can you verify the correct part number I need? There was no tag on my original harness. I had ordered one off eBay several months ago and had tried it before this one and found it was wrong and missing some connectors and I’m assuming it’s for a 2000 or 2001 as they don’t have a crank position sensor I believe. I have emailed Firsttruckparts but I’m sure they are closed today. I would try to figure out how to remove the pins from the plug and correct this one but I’m sure that’s going to snowball. Again, any help or suggestions are very much appreciated.

John Thanks a bunch for your time and excellent explanation. Very much appreciated. I will do this when I get home tonight and report back. I have read and used forums like this to help me over the years but have never contributed when I figure something out and you have inspired to take the time and share.

I haven’t tried the old ECM but I will. I know nothing about the internals of the ECM but I’m not seeing how it can put out the needed 12 volts and drop when the relay is plugged in. I wouldn’t think it would take much to just pull in the contact. I could see if there was an issue with the VP after it pulled in causing the voltage drop but I have the VP unplugged so all it’s trying to do is pull in the contact. I really wanted to get everything back to original by doing all this but I’m starting to think maybe just using a key on signal from somewhere else. Thoughts on that? Will it cause any other issues? Interested in the “ dirty fix”.

I was just out messing with it again. Tried to test for voltage at pins 48 and 50 but without the ECM being plugged in it causes the No Bus and no power. I’d rather not penetrate the insulation on the wires to test. Will a non contact tester work or do you have a good way of testing those with everything plugged in? Thanks again for your help and input. Several days messing with this and restless nights. Been a mechanic and maintenance guy for 35 years and been stumped before but can’t remember a more frustrating problem as this. I guess what I’m asking is how would I use a test light in this situation to find the poor connection.

Thanks for the reply. I was in a bit of hurry when I posted and left out a couple things. After the ECM and harness replacement the WTS and lift pump issue is fixed. When I was first troubleshooting the lift pump issue before ECM replacement and before I studied and understood the wiring diagram I pulled the fuel system relay looking for issues. I pulled the cover off the relay to check voltage because I couldn’t get my meter probes onto the spades. In doing so I accidentally shorted the relay and blew fuse 3. Replaced it and was back to square one with LP and WTS. So then I replaced ECM and harness. Got done and the WTS comes on lift pump cycles. I primed filter and had fuel to VP. Tried to start and cranks but wouldn’t start. Traced it down to no voltage at VP. Then I went back to the relay and if I jump 30 to 87 I had voltage to VP and truck starts and runs fine. That’s when I kept digging and figured out I only lose voltage to pin 86 when I plug relay in. I never lose voltage to pin 30. I will go check pins 48 and 50 with relay plugged in and see what I get. To confirm what you said about resistance not always showing the problem, when I accidentally shorted the relay a bunch of other stuff started happening like ASD relay buzzing and no gauges and no bus on odometer which all lead to fuse 3 being bad. I checked it probably 20 times with ohm meter and it checked good. Finally swapped it with another and everything went back to the way it was. Tore the fuse apart and you could see where it was “blown” and barely touching. Thanks again and I’ll let you know what I find

Hey guys. I have a 99 Dodge 2500 quad cab 4X4 5 speed. I was having an ongoing issue with WTS light either being delayed or not coming on at all and LP not cycling so I replaced ECM with a known good one and replaced ECM wiring harness with a new one I found at Firsttruckparts. When I was troubleshooting LP not running( before I replaced ECM and harness) I pulled the fuel system relay and got a P1689 code and truck wouldn’t start. So now, after replacing those I still had code and no start. After a lot of troubleshooting and wire checking I figured out on the fuel system relay that I have 12 volts to pin 86 from ECM until I plug the relay in and then it drops to about 1.8 volts. I sanded and dielectric greased all the grounds. I finally ran a dedicated ground to pin 85. Same thing. I have the plug unplugged from VP 44. I have checked resistance on wire from pin 86 to the ECM plug and it shows 0 resistance. I’m lost at this point. I don’t think it’s the ECM as it has 12 volts until relay is plugged in. Any help would be greatly appreciated.