Don't replace the old one. I had the same thing happen and many dodges have the same problem. As long as the fuel sending unit is working the problem will lye in the voltage limiter, it is on the rear of the cluster and drops the voltage down for the gas gauge and temp gauge. If you don't replace it you will likely burn out the temp gauge even though you've disconnected the wire to the gas gauge. My problem was a combination of loose gauges and bad limiter. I order the plug n play one below. Do a search here on the voltage limiter and you'll see its your problem.