When ever I drive my truck in the rain my water in fuel light will come on. It will then go off when I drive when its dry. Is there a sensor that gets wet and turns it on? Any suggestions?

Do you still have the stock fuel filter housing? If not and the unplugged wire hanging there is getting wet it will trip the light just like you mention. But if you do have the stock filter yet look on the side of it and check if the WIF wires are plugged into it. Then unplug it and put some dielectric grease in the plug and plug it back in. This should cure the WIF light problem.

Not weather-related, but I know if I tighten the sensor on my 12V a little too tightly, it'll trip the light on. Just had to back it off a hair or two, and it operated properly after that. But along the lines of what M73M said, I'd venture to say you're getting moisture in a connector somewhere..

Because you have the FASS 150, I'm guessing that you are not using the OEM fuel filter housing, and have probably removed it from the engine. If so then the WIF sensor thats dangling and hopefully tapped up will still measure any moisture it comes in contact with.

Sounds like what mine does b/c I don't have the stock canister so when I go through a car wash or in a really heavy rain it will get wet and come on for a while. I tried putting some tape on it, then that fell of so now I just don't worry about it. It only comes on once in a blue moon.

If that plug is not in use, silicone sealer or liquid tape (when it's dry).