I hope you guys are not expecting to use all 19 gallons out of a 19 gallon tank. Most sending units will read empty when there is at least 2-3 gallons left in the tank, and you should fill up then. If you are putting 15-16 gallons in the tank at the station, you are pretty much empty as far as this system was designed.
I would expect the same for the 38 gallon tank. If you are putting 34-35 gallons in it at the station you were considered empty.
Well said! Every OEM has the gauge read E with some percentage left. It's even in the manual, typically. That percentage varies but is often 15%, and even more on my medium trucks at work.
So I think any of us fixing/modding/replacing the sender would be wise to follow suit, for your own sanity and anyone that borrows the vehicle, too.
I did the 38 gal bronco tank mod and when I forget to switch tanks until it's too late(doh), I will get 36 gallons in the rear tank on fill-up. I have just a fuel-rated hose going to the very bottom with a Vee cut in each side.
(My fuel sender plug doesnt have the tabs that hold it into the socket and its popped out...hence me running out of fuel on accident a few times.)