1986 c2500 GMC fuel gauge duel tank issues

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Dukester68

Member
Joined
Sep 25, 2024
Posts
36
Reaction score
33
Location
Arizona
First Name
Gary
Truck Year
1986
Truck Model
c2500
Engine Size
350
Hello my square body experts! I have a 1986 c2500 GMC. It belonged to my FIL and we took ownership after he passed. Its a California 350 and only has 66,000 original miles. Its in beautiful shape and we are keeping it original. That being said i have a gauge issue. I have watched all the you tube vids and was pretty convinced it was the sender units. I have replaced both sender units and cleaned up the grounding areas on both sides and replaced the fuel lines. Im still getting wrong readings on my gauge when on the drivers side tank. The right side tank reads almost empty as it’s probably correct but when i switch the tank back over it only goes up to a quarter plus, it is full of fuel… I pull the connection on sender separately and both go to full on the gauge. I can hear it switching and it runs on either tank. Im stumped. I have left the bed backed out about a foot just in case i need to get back in there. I have swapped out the new senders but still get same results. Im not thinking its a gauge issue but im not sure. I have had the dash and gauges out when i had the dash redone. Could it be an issue at the tank selector switch under the truck? It switches but thats when the gauge fails…………Thanks on advance for the help…
 

Attachments

  • IMG_9663.jpeg
    IMG_9663.jpeg
    172.2 KB · Views: 9
  • image.jpg
    image.jpg
    126.6 KB · Views: 11
  • image.jpg
    image.jpg
    112.6 KB · Views: 9
  • image.jpg
    image.jpg
    175.9 KB · Views: 10
Last edited:

ali_c20

Full Access Member
Joined
Sep 20, 2016
Posts
1,371
Reaction score
1,970
Location
Austria
First Name
Alexander
Truck Year
1974, 1979
Truck Model
C20, K5
Engine Size
350, 350
If it was a gauge issue it would not work on 1 tank.
The gas gauge pegs out over full when there is no ground.
Does it do the same when you disconnect the ground on the passenger side sending unit?
I would check: The selector valve wiring. The selector switch wiring. The sending unit ohm readings with a multimeter.

What is the black wire end in the picture of the driver side tank?

Nice clean truck.

Good video on GM gas gauges:

xc_hide_links_from_guests_guests_error_hide_media
 
Last edited:

Forum statistics

Threads
44,563
Posts
961,143
Members
37,053
Latest member
jg57sc
Top