2005 Toyota Matrix - INstruments go nutty

I have a 2005 Toyota matrix with 123,000 miles. Tachometer, temperature gauge, and AC compressor seem to go haywire only intermittently especially on the initial start up. After a few minutes of driving it does seem to clear up but has been ongoing. What is the cause?

Bad ground connection is my go to. Might be a bad instrument cluster.


Also monitor battery voltage before and right after starting, >12.5V before, 13.5-14.5V after.
Check condition of serpentine belt and pulleys.


A friend of mine had bad ground right at where it gets to the battery negative terminal, it went completely haywire, the vintage of Matrix is around the same mid-2000.
The trouble is that it’s more than one grounding wire going into that point, and connections are crimped in the way where visually it looks OK, but ground is quite bad already.
The fix was trivial - get aftermarket clamps, make sure things are tight.
He later replaced the wire/clamp to OEM Toyota, it was not that expensive at the dealer’ part counter.

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A bad connection to ground or possibly power is most likely causing the issue. To see if it is a ground problem you can make a jumper and connect it to a suspected bad ground point to see if that makes a change. You can do the same with the power but be careful not to place power where it shouldn’t be.