Trouble with gauges

Alright, this problem has been plaguing me for weeks now. I have a 1974 Dodge Dart custom. My gas and temperature gauge do not work. I started by taking apart the cluster, checking the gauges for functionality, and fortunately they work. I decided to replace the IVR while I had the dash apart. Still not working. Next I tested the temperature sender. It works correctly and has the correct resistance. I then checked that all connections all the way to the cluster pins were solid from the temperature sender, and they were. I’ve recently tried hot lining the top pin on the cluster, which heads to the idiot lights, and the IVR and in turn the temperature and gas gauges. When I hotline the gauges they work but I have to disconnect the battery before the gauges are pinned and will ultimately fry. Is the top pin on the back of the gauge which is labeled as (a) a supply for power? Or what am I missing. I just am not sure where to go from here. One thing to note. I’m missing a bulb socket for the brake light on the cluster, could this be causing serious issues with the total circuitry? I’d think not, but I’ve been told these clusters are complete systems and that one small problem can ruin the darn thing. Thanks for any help. I’m just stumped.