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Speedometer and Tachometer not working properly?

Tiny
RODJAMES
  • MEMBER
  • 1992 GMC SIERRA
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 300,489 MILES
My speedometer gauge bounces up and down periodically and most of the time reads max speed. I’m not sure if this is normal but my rpm gauge seems to be reading a lot higher than it should. How can I fix or diagnose this?
Saturday, March 16th, 2024 AT 3:03 PM

2 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Yep, this goes wrong when the cluster is going out or the system has a bad ground. I would remove the cluster and check the wiring connectors for corrosion. The ground is the black wire which a would test with the cluster disconnected.

This guide can help:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

If the ground is good, I would try a rebuilt/used cluster. Check out the images (below). Please let us know what happens.
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Sunday, March 17th, 2024 AT 11:13 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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Anything?
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Saturday, May 11th, 2024 AT 12:39 PM

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