I'm looking to find out what's the cause of my fuel readings on my gauge to be thrown off.

I have an 86 1/2t silverado w/ dual tanks. Well the gauge reads full or past full unless I turn my lights on, then it reads empty until I start the truck up and it reads the full or past.

Have replaced both the grounds on the sending units (wire ends) and looking to find out if I need to replace the sending units, selector valve or if it's something else.

Also when I use the selector switch one tank reads full and the other reads past so I only use the drivers (changes full and past still).

Now I didn't wire the switch so could this be something too?


Need to know soon so any ideas let me know.


Thanks.