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fuel guage reads past full all the time

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R72K5

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on the 77 with dual tanks the fuel guage reads past full all the time and nothing else, never moves

sounds like the wire is disconnected/broken somewhere ?

or ground it lost somewhere ?

(open in the circuit)

what should i check first?

and how can i get the fuel system switched to the driver side if the system is not working

is complete system all intact though

thanks for anything
 
wish mine read past full, well at least you never have to worry about running out of gas! haha sorry but i have no idea
 
i have the same problem, would ihave to take off the dash to look at the wires or can i just look above the fuse box?
 
Your best bet is to start at the tank IMO.

Very common, and likely, that the connector(s) at the tank are broken or corroded beyond recognition. You can't hurt anything by removing the ground and cleaning it up, plus while there you can test that the sender is not at fault.

Of course interior wiring can be messed up, PO's do all sorts of crazy stuff, however, the gauge uses the same connections everything else does on the cluster (except the single sender wire) so if everything else works, it's likely not in the cab that your problem exists.

Good look identifying visually ID'ing single wires under the dash unless you've done it a few million times, it's a spaghetti nightmare. :)
 
on my blazer i had a similar problem, and i ended up running a jumper wire with aligator clips from the tank ground, to the frame...was susposed to be on there just long enough to see if that fixed my problem, and it did fix it.....and well two and a half years later that jumper wire is still there..lol one of these days i'll get under there and fix it proper..
 
mine did the same thing when i did my engine swap. i had to redo some of the wiring and accidentally wired the gauge to 12+ rather than the sending unit. made the gauge read at about 3 o'clock.
 
Last post in this thread might help. http://coloradok5.com/forums/showthread.php?t=69917&highlight=fuel+gauge

To simplify matters, throw out the resistor parts, and replace 90 ohms with "connect to nothing, gauge should peg full" and replace 0 ohms with "connect to good ground, gauge should peg E".

If it passes that test, then the gauge isn't the issue, nor is the wiring there to the gauge from the point you tested, ideally at the inline fuel gauge wire connector near the tank.

Also, I believe in a *dual tank* setup, GM used two different methods for running the gauge wiring. I recall my dad telling me that his '74 dual tank setup switched the tank sending unit wire at the tank switch, and at some point I believe GM got smart and started switching them at the tank switching solenoid.
 
see this is where i am confused

mine already reads empty- or just past it- all the time

it is switched onto the right tank and is the only one that works currently

so definitely means theres an open in the circuit right ?


how should a 77 dual system be wired up ?

anyone know the wire colors and where they should run ?

i know theres that light tan/brown color wire thats supposed to run from the fuse panel to the tank(s) and always is tucked into the driver side step plate rocker crevice

but other than that i dont know, even though i have dropped alot of these tanks in the past, but i never really paid attention to wiring



hmm

so at this point so far i figure that if the wiring looks ok- at the selector switch in the dash- then the problem is surely gonna be somewhere under the cab or in the rocker wiring crevice


no ?

this has to be one of the extreme top stock/factory problems with these truck, heh

thanks!
 
oh and which is full and which is empty-

90ohms

zero ohms

seems like zero ohms is full since when there is an open in the circuit it goes over to full or past it


right?

so if i take the sender unit wire off the unit- and put a resistor inline with the wire end and the chassis ground- then it should go to empty

IMHO


thanks :D
 
ok so infinite resistance is what would cause the needle to go to full or past full

keep thinking backwards :O

thanks
 
If the gauge reads right for one tank, it can be assumed that at least the gauge itself is good, and so is the wiring past wherever the two tank sender wires merge.

My dads got a similar issue, one gauge doesn't read for squat, the other reads fine.

Sorry can't help with the year splits for wiring, you might be able to dig up a few posts that have wiring diagrams in them, or dremu's brochure page?
 
both tanks dead, needle never moves, its all dead, i hate dual tanks, always seems to be this problme with them, more likely than with single tank


i found Aaron's wiring pages on slosh but nothing related to tank wiring at all, no where even close
and it looks like everything there is just for K5's only anyways


hmm

i may just end up dropping a tank and runnign single wire and 3/8" line and eliminating all the dual tank BS, its all nothing but trouble



thanks :D
 
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120 ohms resistance in the right tank and 93 in the left

is what ive got

the right tank is a brown wire and the left tank is a blue wire

theres another brown wire under there in the same harness and it is cut off under there and goes to nothing, and so does a green wire

then at the dash switch is a pink wire in the same harness, but it doesnt go under the truck

i assume the pink wire goes to the fuel guage

what is the second brown wire and the green wire for ?

one is for the switch valve assembly which only has one wire spot

why is there a second brown wire ?

they all these wires run from RH side of truck where the valve assembly is and over to the driver side and meet up with the blue wire out of the LH tank and then run up the frame rail into the firewall straight to the dash switch

very basic simple

and i cannot get the needle to move, i even tried jumpering the pink wire with the brown wires and the blue wire,

to no avail, was a little of a spark though between the pink and the brown or blue wire


how can the switch valve assembly only need one wire to run it ??

wierd ?

ideas ?

thnaks
 
nope the pink is hot as heck

i grounded it and it blew the fuse

apparently none of the wires at the dash switch go to the guage

because all the wires thaty comes off the switch- other than the pink- go straight through the firewall and to the tanks/unit stuff

what the hell ?

oh and the browns are actually tan, one is striped and the other is solid and it is connected to the RH tank sender

the striped one is cut off at the unit under there

and so is the green one

which plugs to the unit and whats the other for ?

i assume the green goes to the unit and gets switched from hot to not hot

hot coming from the pink wire at the dash switch

i took another fuel guage and i connect one side to the pink wire and the other side to the blue wire and it pegs real quick over to full or hot- i forget which

and i connect the solid brown wire to where i had the blue wire and it pegs again

i know that hot is at the guage all the time with the key on, so i know im doing it right

i dont know what the deal is and why theres no wire from the dash switch to the guage ??

wth ?

thanks
 
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Well, then we need to figure out which wires come from the tanks (sending unit wires) and where they go, so you can test that the gauge isn't an issue.

NOW I think I understand what you were saying before...the tank switcher isn't working, and your fuel gauge works for neither as well. Correct?
 
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