quick pyrometer gauge??
 

I did not install my pyrometer it was done by a shop. Ever since like a month after it was installed it has been going crazy and going up and down (its a mechanical gauge) sometimes it works but if i turn on my headlights or turn on my rear defroster it will go crazy if i have both my lights and my defroster on it just goes completly dead. Just wondering what you guys think maybe its grounded wrong or something i just want it to work and i was hoping you guys could help me narrow the possibilitys thanks.

take it back the shop

Sounds like a ground offset problem...If it uses a amped up thearmocouple the chassis ground needs to be pretty close to the T/c grounds Voltage or else you will run into problems.

were are the t/c grounds