I was assuming it was a 94-96 B-body, with an LT1, and no towing package. They all are setup the same, in the this area.
The fan on the drivers side will not come on unless the pass side fan can't keep the temps under control, or get the A/C head pressure under control. When you unplugged the sensor at the WP, you put the car in a limp mode, protection mode, whatever you call it. The PCM doesn't know what temp the engine is running at, so it kicks both fans on.
The gauge on the dashes of these cars(Roadmaster, Caprice, Impala SS) can be hard to trust. It's sweep from "Cold" to "Hot", might not be that much of a difference in actual coolant temperature. I'm not familiar with how close the 96 SS gauge is, since it is different than the 94/95 Impala SS cluster, which is the same as the ones in my 94-96 Caprices. Cruise down the highway at about 75mph, and see where the gauge runs. At that speed, there is enough airflow, that the fas are not needed. I can't remember the speed thresh hold for the fans to turn off, but I'm fairly certain at 75mph, they are off. Typically, the car will run about 15* F, higher than the t-stat opening temp. So for the factory 180* stat, that is about 195*. When I do this, my 95 Roadmaster runs at about 175*. I know this, because I can go into the climate control, and get an actual reading the PCM see's. In *C. Both of my Roadmasters have a 160* stat in them. This Roadmaster doesn't even HAVE a primary electric fan. It has the towing package, so it came with a primary mechanical fan. I removed this fan, put the primary electric fan on, and never wired it up. Even while sitting for long periods of time, the secondary fan doesn't kick on often.
The gauge on the dash, gets it's reading from the sensor in the passengers side head. I strongly suggest swapping that one.
Do these engines really get that hot?
Oh yes. The Reverse cooling is great. The engines can get really hot, and the heads are cooled first. The T-stat is 180* stock. But, it doesn't hit 180*, and then fly open. It has a dual element, so it opens slower. It is also effected by the "cold" side. But, the programing in the PCM is set so the fans don't come on until the engine really gets hot. I think the temps are actually 224/234* F for the primary/secondary fans to kick on. There are a few reasons, why we think GM did this. The hotter the engine, the lower the idle emissions. Less wear on the fans, so they will last longer. Who knows. But on the flip side... LT1's LOVE to run ice cold. The colder you have them run, the more power they make. These engines feel slow, as if they have lost quite a bit of power, when they are running around 230*. At the points when the secondary fan actually kicks on, you can tell the motors are hot. A simple reprogram of the PCM can change this, so the fans come on sooner.