Low Voltage.....?

[John Crouse]

Hi All. 

I have got a real puzzle. The volt meter (analog) on my dash when cold reads just under the 14 volt mark. As it warms up it drops eventually to just above the red zone. I have changed out all my cables with heavy duty cables, cleaned all grounds I could find, being that both were old anyway, changed alternator and battery for top pole battery., swapped out Ecm (swapped back), and still the same. Here is the real puzzle for me. I have checked with my multimeter the continuity of the battery cables and when running, tested the volts. With multimeter everything is good to go and reads 14 volts. So guys, what do you think? 

Edited August 6, 2022 by John Crouse

[richard wysong]

so it's just the gauge that's not reading correctly? It's 14v even when the gauge says it's not?

[John Crouse]

Correct.

Since writing this, I bought (to much money) a 200 Amp Alternator and it is worse. Also spiratic and the needle jumps up in volts as soon as the rpm's go up when starting to drive although, it doesn't read as high as the first new alternator which is 105 amps. When engine is warm, In idle, stopped and in drive, is when it gives off the worst readings. all plays out on the dashboard volt meter. With multimeter everything is normal. Could it be a ground under the dash? And how could the higher Amp Alt be worse than the stock Alt? Clearly not clear.

Any thoughts? One quick note, other than this, the truck works fine. 

Edited August 6, 2022 by John Crouse
Added thoughts

[CamGTP]

Sounds like a bad stepper motor for just that gauge or an internal wiring for the cluster is going bad.

Edited August 6, 2022 by CamGTP

[greatmizzou]

Do all gmt400 clusters use that weird plug in the back versus individual connections?  

[richard wysong]

yes but not all clusters are interchangeable. I do not know what the differences are but did a swap in my 98 and the speedo was off, I had different indicator lights than the original. that truck the voltage gauge was also inaccurate and would read lower with the lights on. I always suspected a bad ground to the cluster

[John Crouse]

3 hours ago, greatmizzou said:

Do all gmt400 clusters use that weird plug in the back versus individual connections?  

The entire cluster has what looks like a hardware plug which goes out from there with flexable laminated circuit plastic sheet to the individual motors and lamps. 

[richard wysong]

yes but not all clusters are interchangeable. I do not know what the differences are but did a swap in my 98 and the speedo was off, I had different indicator lights than the original. that truck the voltage gauge was also inaccurate and would read lower with the lights on. I always suspected a bad ground to the cluster. I would just add a seperate aftermarket voltmeter and be done 

[John Crouse]

6 minutes ago, richard wysong said:

yes but not all clusters are interchangeable. I do not know what the differences are but did a swap in my 98 and the speedo was off, I had different indicator lights than the original. that truck the voltage gauge was also inaccurate and would read lower with the lights on. I always suspected a bad ground to the cluster

Wouldn't a weak cluster ground effect other gauges? 

Edited August 6, 2022 by John Crouse

[Brian Lindsey]

there are several companies that can fix your gauge cluster , i had mine done from a company in florida , but i know of another company in new york state, and im thinking another is in washington state, i know the first two , but third one i had just heard about it

[John Crouse]

Thanks all for your awesome input. I have kept an eye on this over the last few days and I am certain you're right with the little volt needle motor. I'll be looking into the fix. Again, thanks much.