Serial Data Question. Truck Cluster. Tach but no temp or fuel
 

I am running a stock 99 Silverado gage cluster in my 75 mercedes LR4 swap. The tach is working but the water temp and fuel gage (I am using the silverado float/sender in the MB tank) are not. My understanding is that all 3 of these signals come from the ecu through a grey wire to the cluster. What should I check?