93 K1500 Speedo/odometer intermittently function

[motorhead327]

I have a 93 K1500 with the 350 and the 5 speed manual transmission. starting last fall the speedometer would randomly drop to 0 and if on cruise it would cut out not too long after i noticed that the odometer would also stop reading when the speedometer stopped working. fast forward to now where the Speedo only works on occasion mostly on right turns and the odometer only registers 1/3 of gps mileage on average. the shift indicator is also out of whack. i have replaced both the vss and the vssb to no avail so i turn to you for help. My electronics background is telling me is a bad ground but i haven't been able to find any as of yet.

I know that sometimes other seemingly unrelated issues are in fact related so the others that i have are: park brake light is almost always on, the temp gauge hasn't worked in the time I've owned the truck, the drivers side door doesn't turn on the cab light when opened (passenger door does).

I changed out the circuit board behind the gauges I'd start there.......paid only $75 for mine used.

 

[someotherguy]

I changed out the circuit board behind the gauges I'd start there.......paid only $75 for mine used.

Your 1989 gauge cluster is entirely different from a 1993. 1988-1991 are one circuit design, and are known for problems with the speedometer going intermittent. 1992-1994 really don't ever go bad in the same fashion.

Richard

 

[jus10inbrla]

Under the dash and just behind and up above your aldl port is a bracket that should have a small ground wire screwed into it.
That bracket from the factory is bare steel and it rusts.
The weak little screw is some kind of a zinc plate self tapper but it is a ring flange self tapper. As are most of those small ground screws.
In other words, when you pull it and look at the bottom of the screw head.
It is not flat like you would expect.
It only contacts through a very thin ridge that runs around the outer diameter of the screw head.
No matter how good that thing looks, pull it and clean the base metal of that bracket and install a better screw.
No matter how good it looks
All kinds of strange random instrumentation problems are caused by that one little ground.

@Muddy STRONGLY suggest checking this ground and hitting itand the contact point with a wire brush. Its the main ground for ALOT of circuits. Even tho its maybe only a #12

 

[Muddy]

@Muddy STRONGLY suggest checking this ground and hitting itand the contact point with a wire brush. Its the main ground for ALOT of circuits. Even tho its maybe only a #12

I am not seeing it anywhere

Sorry it’s been a while. Life happened.

 

[jus10inbrla]

thats proly your culprit then

 

[Muddy]

I mean I can’t find where that bolt is i’m not sure if I’m just missing it

 

[jus10inbrla]

Just find the single ground wire somewhere behind the knee bolster. The eye has ridges on it.

 

[Muddy]

Just find the single ground wire somewhere behind the knee bolster. The eye has ridges on it.

Ok

 

[Road Trip]

Under the dash and just behind and up above your aldl port is a bracket that should have a small ground wire screwed into it.
That bracket from the factory is bare steel and it rusts.
The weak little screw is some kind of a zinc plate self tapper but it is a ring flange self tapper. As are most of those small ground screws.
In other words, when you pull it and look at the bottom of the screw head.
It is not flat like you would expect.
It only contacts through a very thin ridge that runs around the outer diameter of the screw head.
No matter how good that thing looks, pull it and clean the base metal of that bracket and install a better screw.
No matter how good it looks
All kinds of strange random instrumentation problems are caused by that one little ground.

@thinger2 is on the money with his guidance. Here's a couple of illustrations from the '93 FSM
to give you a visual clue or 2 about what he's talking about.

By the way, the ground that affects nearly everything in the cab was named G202 by the General.

Physical location illustration:

You must be registered for see images attach

And after all these years the factory splice where all the fanout is performed is also of interest
if the bad actor circuits still act like they are victims of a sketchy ground while the rest of them
continue to work as advertised:

S(plice)207

You must be registered for see images attach

The wiring diagrams for these trucks are pretty decent, and take a lot of guessing out of
repairing electrical gremlins like the ones you are suffering from. If you haven't downloaded the
ones for your year already I'd highly recommend you give yourself this unfair advantage.

Hope this helps. Happy hunting!

 

[someotherguy]

Look at the diagnostic (ALDL) connector under your dash. Lay down on the floor mat and look behind the dashboard at the metal tab it's connected to. Behind the connector you'll see that single black ground wire attached to the same metal tab with a screw.

Richard