I know it's been covered but after reading all other posts relating to the subject I'm still having a problem.

Details:
Original fuel tank select valve was leaking from the connector plug. Both tanks worked and fuel gauge worked for both.

Switched to the Pollak and wired up the weather pack connector. Truck runs off both tanks but gauge only reads correct on front tank. Rear tank reads empty.

Searched all forum posts and advice and figured out I had main sender and aux sender wires reversed on harness. Switched them around and now have correct reading on rear tank and empty on front tank even though I topped it off and it's full.

currently wired as:

Orange > E (main tank)
Brn/Wh > D (aux tank)
Y/lt Bl > C (aux sender)
Y/Wh > B (fuel gauge)
Bl/Y > A (main sender)

This should be the correct wire up but still seeing the gauge issue. I'm going to measure resistance on both sender wires today to see if there could possibly be a short on one. Nothing has changed since everything worked properly except the plug on the end of the wires and the valve. Why is this such a p.i.t.a.?

 

did you read the simple way i ended up doing it here?
with stock connector cut and in hand,this will become all so clear and 'so easy a caveman could do it'.no meters nor testing anything required.
in other words,you can put the meter away.the stock connector you cut,provides your schematic for you.with each connector in hand,and the info listed above written down,or printed will all become so clear,and easy.you'll wounder why you struggled once its clicks.
now,if something doesn't work after following that,that either something was wrong already before you started,or it just happened.in which case,the FSV may not have been bad,then problem may have just been the electrical.this would really confuse ya. (cus really,you should have tested the electrical before swapping the FSV.in my case i didn't have too.mine went in such a way,that it sounded like an electric fuel pump lol.that's how i knew right away when my engine stopped,to start with that,as i didn't hear it any more.-just got my truck.)
so you would need to start testing things like the switch on the dash board for starters.

however,you say yours was just leaking,and everything electrical worked fine first.so you should be fine once you connect things properly.

when i searched,i threw all the quotes and tips i could find into this thread,and added a boat load more info.
https://www.ford-trucks.com/forums/9...el-gauges.html

 

That was a great read and lots of info which helped. I read and took advice from it the first time I replaced the valve which I did the wire to wire from the stock connector.

Problem is I threw the old one away a couple weeks ago and don't have it for a reference anymore. When I hooked up at first only the front tank read and the rear didn't. After changing the glow plugs yesterday and remaking the harness I decided to go back to the ftsv and fix the problem with the rear tank.

I came back to the thread and searched some others and gathered that I had terminals A and C reversed from your thread. When I swapped them the front tank no longer reads and now the rear tank does. I'm certain I have the wiring right but just want to think out loud so to speak in case I'm missing something that to someone else might be apparent.

I see Dave mentioned sender grounds by the valve which I haven't checked on. Does the valve motor use the ground through the senders to complete the circuit? I'm curious to meter the sender wires anyway to verify and see what they read vs. what the charts say since the front tank is topped off. Maybe I caused a short somewhere during the switch out.

 

yes as noted here:

so if this seems to be the problem,the first thing i would in this case,would be to pull the switch on the dash,and jump it,to then see if the noted info above tests like it should(down on the wires at the FSV.)
if it does when jumped,but not when switched using the switch,then you'll know the switch is bad an needs replacement.
if it still doesn't,then you know the problem is somewhere with the wires.in which case,id probably run new wires myself,as it may be hard to find the short in that run down along the frame rail.it's all wrapped up really tight.check for anything obvious first though,you may see the problem right off.
chances are the switch on the dash is whats also bad.

of course don't forget the first thing........the fuse lol.i guess i shouldn't assume you already checked the obvious.
but since you were able to find the connections via a meter,and not using the stock connector,i guess its safe to say,you've seen power.now you need to use your meter on E and D and test for power and ground,and if they switch back and forth.which is an easy test.
as you can see,this is the point where i stopped and it dawned on me to simply copy the stock connector over.all worked fine,so i had no need to continue diagnoses from here.but it's quite simplistic with the provided info from others like Dave to trace out the problem.
what doesn't add up however,is that all was working correctly before you began.
what are the odds the switch all the sudden blew.
ahh well.you'll know a lot more info when you find the ground and power,and see they if they reverse polarity when you flip the switch.

 

Fuse?? nope haven't checked it.

D & E are verified and they reverse with the switch = switch is good.

Metered both senders and one was 140 ohm and the other was 22 ohm...okay everything good, thinking maybe I just need some gas. Cruise down and put 5 gal in the rear, which is funny cos it's already reading full...

Okay get home thinking somethings not right so I siphon 5 gal out of the front tank and even though switch is on the rear the gas gauge drops off full and further the more I siphon out of the front tank.

So I'm switching A & C again which puts it back to originally how I had it and at least I know reads the rear tank when switch is on rear. This leaves the problem of front tank not reading. I metered the wires after driving around and one now reads 17 ohm and the other won't read.

I'm almost convinced the front sender is bad or there's an intermittent problem in the wire.

If the sending unit goes out does that just controls the gauge right? The lift pump would still be pulling fuel from the tank or would that starve the engine? Since the valve switch, the truck ran fine for a week then would die out after sitting at idle for a while. I thought air intrusion but have double, quadruple checked the lines and my connections.

Rear tank runs steady when I check the flow at the schrader valve. But running on the front tank after a while it dogs out and dies. Problem is from the ftsv back on the front tank which is why I'm starting to question that it's the front sender failing and not the wiring now.

Fun times!