Metal vs Plastic Base Instrument Cluster 1975-1980
One of the major problems with 75-80 Dodge Trucks is amp gauge failure. When the amp gauge fails, the truck stops. The reason the amp gauge fails is excessive heat damage because the plastic cluster base doesn't do any adequate job of transferring heat away from the gauge.
The best solution for this problem is to replace the plastic base instrument cluster with a metal base cluster. The metal dissipates the heat from the amp guage a lot more effectively. The metal base instrument cluster was installed on 1975 Dodge trucks for part of the year after which they switched to the plastic base cluster. The metal base cluster is a direct replacement for the plastic base cluster. The circuit board is different and the instrument light bases are different, but the speedometer, gauges and clear plastic faceplate are the same. The stock cab wiring harness connects without any changes and the dash instrument cover fits over the cluster the same except for minor differences in the attaching screws.
The plastic base cluster will work fairly well in a new truck, but as the truck ages the demand for current to run the heater blower motor and other accessories increases. That is one reason it is a good idea not to run the heater blower motor at its highest speed setting. The heater blower motor switch is a high failure rate item for the same reason.
If you decide to go with a metal base instrument cluster, make sure the leads that connect to the amp gauge aren't badly heat damaged and the fuse block is in good condition. If you remove the plastic base cluster and want to reinstall it, verify the amp gauge hasn't melted into the base. The best way to check it is to remove the two 3/8 nuts and take the amp gauge out of the cluster. If the 2 legs on the back of the gauge are tight, the amp gauge is ok. Then take the 2 screws out that hold the fuse block in place under the glove box lid, flip the fuse block over and inspect the fuse block for heat damage. If both the amp gauge leads and the fuse box components show nothing but minor heat damage the electrical wiring should be able to support the new cluster.
Article written by Joe Leonard 1-07
Joe Leonard 2007-01-23