Hello! I'm new here but I have been been reading forever trying to fix various problems, but especially the speedometer/odometer acting funny. Call me Crambone. I got tired of working on trucks a long time ago from always having to spend all my spare time keeping my junk running so I could get to work so I guess you could say I don't really belong here with the guys who really like working on this stuff. Now I need help because this problem has been driving me crazy for over a decade.

I've been dailying this truck for something like 12 years and since I got the truck the speedo sometimes works but usually jumps down to zero randomly then back to near correct speed at most speeds (or, it used to before I installed the third instruement cluster and now it's 7 MPH fast at 45). I understand this is a common problem and I'm wondering if anyone has figured out the root cause.

This truck has the VSS in the pumpkin, no output shaft sensor in the trans. Only sensor on the manual trans is the reverse switch which works fine.

I changed the VSS twice, changed the instrument cluster twice, and tried a different ecu, and the real kicker is I completely deleted the rotten harness connector with someething like 42 connections in it, the one under the drivers seat.

Through all of this work nothing has changed and it's still a thorn in my side. When the speedo goes to 0 the fuel trim gets whacky and the truck falls on it's face. It's terrible to drive and gets terrible gas mileage, especially on the interstate because it takes constant throttle control to maintain a certain speed (no cruise control)

At this point I wish I had never bought the truck but then I realize if I bought something else I would just have to keep spending time and money on the new one to keep it going as well so i've decided to do whatever I need to do to make this one right.

I've spent probably $6,000 on this truck since I got it replacing everything to keep it going and still haven't been able to figure out this speeedometer issue.

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Today myself and a buddy went through all of the factory testing procedures for this problem except for checking the gray/black wire that goes from the GEM to the instrument cluster but that seems an unlikely culprit.

One test procedure (test black/green wire and red/pink wire) for voltage less than 5 seems to show that the red/pink wire has a short to battery, but the other (ohm test for more than 10,000 ohm) procedure shows normal. We tried all tests with a confirmed ground and with VSS pigtail plugged in and also unplugged from the sensor. When we wrapped it up for the day the speedometer now doesn't work at all, stays pegged at zero, so I don' tknow what happened there. Maybe the GEM finally gave up completely? Or maybe it was the ABS module? But everything else works fine as far as I can tell.

I have ordered a tested GEM and already have a supposedly known good ABS controller to try next week if all else fails.

Next weekend we will connect test wires from the VSS directly to the GEM and see if that fixes the problem. If so we will know there's a short in the wire from the VSS to the GEM.

I have a feeling the Red/Pink Wire and some other whatever +12v wire have been rubbing against each other and are slightly bare and are touching but going by one of the few the test procedures we did this doesn't seem to be the case. Connecting test wires will prove that one way or the other I guess.

If that's not the case we will try the new GEM and then the new ABS controller.

My point in all of this is first to ask if anyone has gone through this entire procedure before and figured out exactly what's been causing this problem for so many of us and second to document what we did when/if we figure out how to fix it.

So, the question is, has anyone gone through this front to back, 100% before and figured out the real root cause? If so, please tell me what you did! If not, does anyone have any suggestions?

Sorry about the long post. I never learned words and communication very well. I know most people could have said this same thing with 5 sentences but my disability makes it difficult for me to explain things the way I'm thinking about them.

Thank you for reading my post and please comment if you know anything.