67' Cj5 V6 Speedometer / Gauge Install And Grounding

Continuation from my post immediately above.....

After studying this document that Timgr posted a link to, Gauge Repair Information, I've at least partially answered my own question. (Thank you, Tim!)

Here are two sheets from that document that clearly explain how the fuel gauge's internal voltage regulator gets grounded to the cluster housing. Note the red "block" shown in these diagrams, which indicates the area on the rear of the fuel gauge that makes this grounding:





This ground connection from the fuel gauge's internal voltage regulator, or CVR (for Constant Voltage Regulator) is intended to contact the unpainted area on the inside of the cluster housing where the gauge is mounted. Here are the photos from Fred's first post in this thread of the rear view of the fuel gauge showing the CVR's ground contact points, and the inside of the cluster housing:






My only remaining question concerns the temp gauge. The document above indicates that it does not it need to be grounded to the cluster housing - but if not, why?

 

No. It receives 5V from the CVR via the insulated strap. It grounds through the "sender" at the engine. It's measuring the resistance of the sender and displaying that as the gauge reading.

The fuel gauge would not need a ground if it did not contain the CVR. The indicator of the fuel gauge grounds through the fuel level sensor in the gas tank. The "CVR ground" is exclusively to power the voltage regulation action, not the gauges.

Glad I could help!

 

Okay, I get it now.

The fuel and temp sending units, being different types of variable resistors which are each connected to ground, provide the grounding for the two gauges.

However, the constant voltage regulator, or CVR, located within the fuel gauge must be grounded to the cluster housing, which is the reason the cluster housing must in turn be grounded to the body.

Thanks again, Tim!