91 K5 (possessed) - I need a old priest and a young priest!!!

[Rhinodrvr]

To the brotherhood, my 1991 K5 (MegaPig) has been possessed!!! After transplanting a GM factory crate motor in, multiple tranny rebuilds....I have finally started putting miles on her. I decided to replace the sppedo with another factory unit that had been reset and reconditioned to track the new miles on the drivetrain. Well this new speedo never worked. I have replaced the VSS and the DRAC module and after finding a third unit....my speedo started working. Now we get into the possession.....about a month ago the working speedo began to bounce around and show inaccurate readings, then the blinker lights quit working, then the service engine light comes on and goes out, then the E Brake light comes on and goes out and now the dash lights have quit working. I NEED HELP, ADVICE, A TECHNICIAN, A PRIEST or some direction to get this correctly working. My dash is completely torn down and I am tired of driving a truck that is non functional and looks like crap.

 

[dyeager535]

I like to figure VSS out with cruise control. Does setting cruise still work? If the speedometer jumps and the cruise tries to match it with throttle, the problem is not with the speedometer.

My *suspicion* is that your wiring to the cluster is screwed up. The contacts on the cluster connector and (less often) at the back of each gauge are problematic at best. You can try to make sure the contacts are good and tight, the only REAL solution with a stock cluster is to hard wire the whole thing.

You can search my username and "cluster" in the title to find what I did. Not the best writeup, but it's got pics linked and part numbers.

 

[Rhinodrvr]

What kind of automotive repair service should I look for to help trouble shoot this? I feel this is outside my DIY capabilities. The guy who did my DRAC module offers a diagnostic service that includes wiring diagrams, online support, etc.

 

[blazinzuk]

Bad ground


Which is my go to answer for anything electrical. Oddly enough correct more than not.

 

[dyeager535]

What kind of automotive repair service should I look for to help trouble shoot this? I feel this is outside my DIY capabilities. The guy who did my DRAC module offers a diagnostic service that includes wiring diagrams, online support, etc.

Pretty much anyone that has dealt with these trucks should be able to handle it. So an old guy lol. But finding anyone you can trust to work on a vehicle anymore? Good luck.

It's not difficult. The problem is that "fixing" it might not work. All you do is remove the gauge bezel, I suspect removing the dash pad will make access quite a bit easier too but probably not necessary. Once you've got those out of the way, the cluster comes out.

It's not likely at all that you have multiple issues. Almost certainly as mentioned it's one thing causing all issues, and on these clusters, both the + and - is just one wire....only takes a problem with one of them to affect every gauge and light on the cluster.

 

[dhcomp]

There is a harness that ties the vss to the trans. 2 wire I think. I will et your bouncing speedo is from these wires shorting.

Mine looked fine, but when I untwisted them, the insulation was all cracked. Replaced the wire, and all was well again

I'd check grounds too.

 

[PWagon]

I had the same problem only mine was with my gas gauge (needle bouncing). It turned out to be a bad connection from the back of the gauge to the circuit board in the cluster. Don't be intimidated by the cluster setup. Like dyeager535 said above, there are a lot of good articles on this site that have addressed this very issue before. Take your time and make sure you repair your cluster the first time. Nothing's more frustrating than having to fix the same issue multiple times.