I have a gas guage that has not worked since I bought the vehicle. when looking at the sending unit i notice that there is just the main wire (1) coming out of the sending unit going back to the fuse box, no ground. my 70 suburban ambulanc has that same wire and then an additional wire that grounds to the bumper. Am I missing a wire or is the sending unit on the 71 k5 ground inside the tank?

1st - :welcome2: from West TN :hi2:

2nd - If memory serves on my Blazer, seperate ground wire ;)

Don't know about the sending unit wire, but welcome from the Pacific NW. Post some pictures of your blazer when you get a chance.

is the sending unit on the 71 k5 ground inside the tank?


Nope, should be outside.

Welcome from VT.

Pretty New To The Board, Thanks For The Welcome. I Am Not Sure How To Post Pics Yet But I Will Try To Figure It Out. I Have A 71 K5 Blazer, 70 Suburban Ambulance, 56 Bel Air Wagon, And An 03 Silverado

Frame is the negative side. The Tan wire is your fuel gauge sender feed. If you unplug it and the gas gauge pegs to the right, it's not the gauge. Most likely the sender, inside the tank, or the brass float ball on the sender arm.
You will have to drop the tank to get to the sender and/or ball. On my '71 Jimmy, I will have to un-rig a tow hitch crossmember, and unbolt a bulletproof shield around the fuel tank. Since I hav'nt had the time to do all this, I keep a mileage log and make sure I don't go more than 200 miles before filling up again. [20 gallon tank @ 10 MPG]. Good luck. And welcome to the board.

look in the FAQ part of the board theres all kinda good info in there
http://67-72chevytrucks.com/vboard/forumdisplay.php?f=28
heres one on posting pics http://67-72chevytrucks.com/vboard/showthread.php?t=209103

Welcome to the board. I agree with Sunshine, probably in the tank. Only a single wire.