Hello Wilson8ford!,
I am experiencing the same freightliner gauge issue you had posted about back in 14'. My speedo, tach and both air gauges work but the other 4 smaller gauges don't work. I can unplug the working speedo into the fuel gauge and the fuel gauge will still not work. Like you, I think I encountered a voltage spike over 7v. In your post, you stated a 3rd party for a aftermarket gauge, who is that? I tried the Colaw RV salvage and they only have a volt gauge. Looking for an alternative to Freightliner's price gouging. Thanks for your time and posts!