1999 GMC Sierra fuel gauge is erratic

Could be a faulty sending unit in the tank or the gauge on the dash.

low fuel light on but still runs good but went that happens that fuel gauge reads empty than low fuel out fuel gauge reads ok whats my problem louis

It would be nice to get a little more detail on the intermittent light - you say "intermittent gearshift indicator light on or black problem" - Would it be ok if you elaborate a little more? Thanks.

As for your fuel gauge - you will be needing a new sender unit. Someone liked to keep the tank full all the time, so the wiper that moves across carbon strips wore them out just on that part. Thats why when your fuel quantity goes down, the wiper moves down to a good part of the sender board.

Ford is real proud of that sender unit - $140.

You can buy one on eBay for about $80 shipped to your door --

sounds like the floater in the tank is stuck dump some fuel injector cleaner in the tank and bounce car little bit to unstick it should fix it

you need to pull pump and make sure fuel float is not bent or hitting side of tank

the sending unit in the tank has gone bad or a wire is grounded out.

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/sean_54c3a3dc48a7773c

The fuel sender is built on to the fuel pump. This happens sometimes if you run the tank low alot Try keeping the truck above 1/2 tank see if this helps otherwise you might need a new fuel pump

My 1999 GMC Sierra did the same thing. Fuel pump went out shortly thereafter.

the fuel pump gage is sticking needs replacement/ its pretty easy if you need to do it yourself/ Please rate my response thankk you very much

This condition is caused by a defective fuel guage sending unit, it is located in the fuel tank