Yes you could have them backwards. As you know, your sender is good. So you've done well so far.
I am changing my advice because I'm approaching it more directly, sequentially and quickly so.......... if a person gets stumped:
Go to the bench:
1. The test ground wire, from the removed gauge, on the bench, must go directly from gauge ground pad to the battery neg post. Always remember when getting a base line/boiler plate reading, there must be NO MIDDLE MEN. (like a cluster ear) (like a "known" ground) Direct test wire only.
2. Test wire from battery neg post to sender flange. Direct test wire only. Battery or power source.
3. Test wire from battery positive post to gauge positive terminal. Direct test wire only. Battery or power source. Fuse can't hurt.
4. Short test wire from gauge sender terminal to sender center tap.
5. As we said in the past, all parts on the bench for testing. Power source can be battery charger or a battery. No truck wiring or truck grounds involved. Just test jumpers on the bench.
Cut out/isolate all possible wiring and ground failures until you get the stuff working together ON THE BENCH. Maybe you did that, can't tell from your description.
Commentary: This is not aimed at you NKkid. This is your first post on this issue. There have been so many, it's time to stop and establish order. Hope it's just your needle. DADS50 is an expert on this whole issue. Good man.
Commentary:
Come on people, this is common sense. In these seemingly difficult fuel reading cases when nothing seems right, can't find the fault, you can not keep asking why why why if you have not tested the sender for ohms, then test the sender and gauge together, doing it outside the truck on a bench. Do all the tests seen it videos posted and explanations posted. There certainly is enough of that info in past posts. YOU MUST eliminate the gauge and the sender from the equation FIRST. Eliminate, as in: Sure they are working. During bench testing we must have them 100% isolated from the truck and isolated from each other and then connected to each other during testing. Then we can move on to truck wiring, ground or power being the obvious issue. We CAN NOT move on until then. We CAN NOT keep guessing if it is the truck wiring, truck grounds, proper power to gauge, bad gauge, bad sender, wrong gauge, wrong sender, backwards hook up, wrong test procedure, wrong voltage, pinched needle, user error.............
After the two components are deemed good, ohm and voltage matched, we then carefully install a little at a time while testing all the way. Any other way is burning daylight. Do the work, we can not pin point it for you.
