To begin, I 100 percent believe my ESS is perfectly operational. It has all required power, everything shows good continuity, and unlike any other ess failure, my A/C works and batteries are charging. I also have overdrive but that’s because it’s a 5 speed. My tach output wire on the pcm (pin 43 I believe) is putting out approx 100-115 hz at idle and it does climb as rpm’s climb. Nothing is shorting to ground or losing power where it needs it. Any suggestions on what to check or just bite the bullet and throw a cluster in it?

 

What are you driving?

 

94 12v

 

There is a service manual for your truck here. I really don't know much about the diesels, so, afraid I can't be much help.....

 

If the tach output signal never drops but the needle in the cluster does it's very likely a problem with the cluster. You could check the tach output signal at the cluster to make sure there is no wiring issue. Then have a close look at the cluster, the connectors are somewhat iffy and the flexible PCB isn't aging well either.