Speedometer becomes tach...help

Larry Matthews

New Member
I'm looking for someone who may have had a similar problem or can help me troubleshoot this problem. My 1995 Newmar Dutchstar is on a Chevy p30 chasis with a 454cid engine. While either sitting still or rolling down the road, when the lights and/or AC with fan are turned on........the Speedo suddenly starts fluctuating like a tach. I have replaced the gauge cluster and the problem still persist. I have checked all the grounds, no blown fuses, everything works fine. My local RV guy cannot find the problem and none of the local Chevy dealers have any ideas nor do they want to take it into their shop. One web RV advisor said that my alternator was putting out too much?????? Anyone have any ideas?

rv wizard

New Member
Speedometer becomes tach...help

You could try disconnecting the altenator and see if that stops the problem. If so then replace the altenator.

Mike & Amy - Fulltimers
Ashley & Candi at school
2000 Gulf Stream Scenic Cruiser on Spartan M.M. 330 hp. & 6 spd. Allison
#3 & #8 NASCAR

C Nash

Senior Member
Speedometer becomes tach...help

With most goofy problems like this ,I have found that it is a ground problem. Ck routing of wires. Let us know what you find

Chelse L. Nash


New Member
Speedometer becomes tach...help

I agree with the ground possibility. I would add a new ground from the instrument cluster to a good frame ground. You can never have to much "ground path" anyway. Bad grounds have been promlematic since the advent of the electric tachs and speedos. JM2CW

Happy Motoring, Butch
2000 Diplomat
1999 Grand Vitara+ toad