I had the same problem at one point. My issue was as was said above, i cleaned out the circuitry very carefully and reinstalled it. I also had issues with my fuses being loose in the fuse block. I replaced the fuses and cleaned out the connections where the fuse sits and now i dont have any issues with any of my gauges or the heater.
2009 KK Sport 4X4
235/75/16 GY Wrangler Silent Armor
Custom Crossrails,Thule Ski/Snowboard Rack,
Silverstar Ultra H-13, Cobra 75 CB Radio W/ 2' Firestik
Relm 8125 Fire/EMS UHF/VHF Radio
1989 YJ 2.5L Stock (for now)