K25 Fuel Gauge Problem
 

My '68 3/4-ton 4wd came factory equipped with saddle-bag tanks in addition to the standard tank. Recently the fuel gauge had begun reading high (3 o'clock position) for the saddle-bag tanks only. The standard tank still reads correctly. I understand that this symptom indicates a ground problem, but since it affects both tanks I was hoping someone could point me to the likely location of the fault. There's a foot of snow on the ground and I don't relish rooting around trying to find it. TIA.

Re: K25 Fuel Gauge Problem
 

I don't think I've ever seen this year saddle tanks with senders. Just a hand valve on the floor and you drove until the engine chugged and switched the valve

Re: K25 Fuel Gauge Problem
 

Are they in bed tanks or bolted to the frame underneath?

Since it is affecting only those tanks I would think it would be the ground from the engine to the frame or from the frame to the bed. The first thing I would do is to run a wire from the NEG battery terminal to the frame and see what that does. You could use a heavy wire with alligator clips on both ends or a jumper cable to test that. If no change go from the NEG battery terminal to the bed. Just make sure where you connect the wire/cable is bare metal on both ends.... That way you wouldn't have to be crawling around underneath trying to figure things out.

LockDoc

Re: K25 Fuel Gauge Problem
 

It has the switch on the the dash to select which tank is being read and the valve on the floor for fuel.

Re: K25 Fuel Gauge Problem
 

Tanks are bolted to the frame with the little aluminum doors in the fenders.

Re: K25 Fuel Gauge Problem
 

I have a hoist at the back of the bed powered by an old Meyer snowplow pump. The motor on it is like a starter motor and draws a lot of juice. It is grounded to the frame under the bed and functions properly.

Re: K25 Fuel Gauge Problem
 

I don't know how those are wired with the switch on the dash. You will have to see if you can find a wiring diagram for it. That might be a challenge....

LockDoc

Re: K25 Fuel Gauge Problem
 

Just curious is a K25 different then a K20?

Re: K25 Fuel Gauge Problem
 

All are k20 no k25

Re: K25 Fuel Gauge Problem
 

Thats a aftermarket auxiliary gas tank there so you will have to sort out how the po did it

Re: K25 Fuel Gauge Problem
 

15 or 1500 is 1/2t and 25 or 2500 is 3/4t. Standard badging for GMC.

Re: K25 Fuel Gauge Problem
 

For GMC!!
Okay, now I get it
Thanks

Re: K25 Fuel Gauge Problem
 

Once the snow melted off I was able to crawl under the truck. Lo and behold! There was a broken wire right next to the fuel valve/tubes. Spliced it and all was good.

After looking at the installation of the fuel tanks, I believe they were a dealer add-on. I was told the truck was originally ordered in Yreka, CA as a plow truck. It has 4.56 gearing and 80 lb. lead weights just inboard of the rear wheels.