The pre turbo will let you know the EGT coming from the engine and the pro turbo will give you an idea how hot the turbo is. Best to wait till the post tempature is 300 degrees before shutting the engine down. If you just have the pre turbo probe, you don't know the turbo tempature. If you only have the post turbo probe, you won't know that the EGT is to high till after it is to late.
I am working on a How-To for installing two Westach probes, boost and guage. Let me know if you would like to take a look at it.
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1999 2500 ST LB 4X4 Metallic Red, 5-speed, 3. 54 gears, LSD, camper and tow package
Westach Boost/EGT (pre and post turbo) mounted on A pillar.