EDIT: 1990 E150 5.8
The issue in question is that the fuel gauge isn't working. I removed the middle fuel tank because I couldn't find a seperator worth a damn and recently installed a new tank with sending unit and pump as well as the high-pressure pump and filter... basically replaced everything. I have since not had any issues at all as I did with the dual tank set up (stalling, acting up on WOT, etc.) but the stock fuel gauge stopped working. I caulked it up to maybe the mid-tank wires still there or some kind loose end somewhere. Well, I have pulled the harness, removed the mid-tank wires, double-checked that I had the right wires running from the rear-tank and got a simple aftermarket fuel gauge I am still it is doing the same thing.




But before pulling the harness I tried to simplify the fuel tank selector to what I thought was just the bare necessity. It obviously didn't work because the schematic I found had the rear and front tank wires swapped and heres where things got wonky. As you can see below (and with the crossed-out colors on the schematic I drew) I thought it was the brown and yellow / light blue was the rear tank but it was the orange and brown / white. but the thing is the damn rear pump worked the whole freakin time. The drawing I have above is what it is at now... which includes splicing in the inertia switch. I can't wrap my head around it! Everything still works fine it's just that the gauge doesn't. It does budge a little... so I know it is getting power, it even has it own fuse space (isn't a dual fuse thing). It's almost like the sending units arm is stuck but thats about it. I really don't want to drop the tank because I just finished that dang job (and seriously kicking my butt for not checking beforehand) but that pretty much all I can think it is. I just need a sounding board to make sure my schematics above should work and that dropping the tank to check the resistance on the unit is next. Its night now but I can get a pick of anything tomorrow morning if needed. Thanks for any help!

 

How about listing the year, chassis and fuel type for whatever you're working on? Maybe edit your post including it in the very first line?

 

Whoops totally forgot that part.