[Southpa]

Not that it makes any difference but the pass. side sending unit (from factory) is for the TCS system (Transmission Controlled Spark) which was installed in 1970 and later motors for emmissions control. The wire connector for that sender is a flat tang where the coolant temp sending unit has a little knob. The usual location for the coolant temp sender is on the driver's side between the 1st and 2nd sparkplugs. If you bought this sender yourself and its the right one (for the coolant temp gauge) then I guess it doesn't really matter where you install it. Otherwise, there could be a grounding problem. Check all your ground straps from engine block to frame (should be one on either side of the engine near the back) and check grounding from frame to cab, located near cab mounts. Unhook them and clean the contact areas with rough sandpaper.

I had the same problem myself, gauge was reading too high and I suspect the gauge wasn't up to snuff. So I opted for a mechanical gauge/sender unit. They are a complete package, just run the sender thru the firewall and install then mount the new gauge somewhere on, under or near your dash.