Mystery cable under dash

[tucsonjwt]

When removing the HVAC duct under the dash of my 83 Chevy C20 to replace the heater core, I found a loose cable. It is 20" long with 3/4" brass fittings on each end. The brass ends are both squared off. One end was fitted into a plastic insert in the ash tray frame under the dash, the other end was loose (somewhere at or near the firewall?). (Photo attached, but not a good photo.)

Does anybody know what this cable is for? It has the number "2526" stenciled in white lettering on it.

On a side note, after I removed the cable I ran both of my dual tanks low so that I could add a fuel cleaner (per label instructions), and now my fuel gauge reads 1/4 full all the time, after I filled both tanks. Could the cable be related to this, or did I just kill the old sending units by running the tanks low?

Thanks.

[Big Port Jimmy 6]

IIRC Fiber optic light for ash tray/lighter One end to an instrument light other end to a clip int the ash tray. Jay

[old Rusty C10]

nothing for the ash tray light right?

[ElGracho]

That is the ash tray fiber optic light. It doesn't have anything to do with the way the gas tanks read. It goes on the lower right bulb in the instrument cluster.

You can't "ruin" a fuel sender by running the tank low. It's a variable resistor actuated by a float. Clean up all of your grounds (tanks to frame, harness near fuel valve to frame, cab to engine, battery to radiator support) and your senders will probably work again.

[tucsonjwt]

Thanks everybody.
I will clean up the grounds and report back. I think these are the original sending units (27 years old?), so their time may have come.
I did disconnect the power supply connection to one of the tanks and the gauge read full. Does this mean the sender is bad?
How exactly do you use an ohm meter to check the sender? One probe on the power supply connection and the other probe to the ground connection - zero resistance is open (broken sender)?
As you can tell, I am as green as you can get in these matters. But I did change a sender on my old 1976 C20 once (dual tanks also). By some miracle the fix worked.
Fortunately, I have a dump conversion on this old 83, so I can lift the box and get at the sending units easily. I don't know if I can remove them without dropping the tanks, since the cab partially blocks the sending units.

[tucsonjwt]

I checked resistance at the fuel sending units (supply terminal to ground terminal and tank) - result was 102 ohms on a full tank. I cleaned ground connection to frame and cleaned off the ground connection on the sending units - no change.
Could the floats on the sending units be damaged and not rising to the top - which is why I only get 1/4 tank readings but have resistance in the units, indicating electrical continuity in the circuit?
The fuel gauge does move slightly when I switch from one tank to the other, and the gauge goes to full when I remove the power supply wire from one tank, so I wonder if this means the gauge is O.K.?

[kris's66lwb]

does anyone habe any more infor on this fiber optic cabel ? i just found it on my floor too

[Fer79]

Originally Posted by big port jimmy 6

iirc fiber optic light for ash tray/lighter one end to an instrument light other end to a clip int the ash tray. Jay

+1

[kris's66lwb]

what does it doo i shine my led flash lite thru it and it wasnt very bright i cant see it being of any use at all

[ElGracho]

Originally Posted by kris's66lwb

what does it doo i shine my led flash lite thru it and it wasnt very bright i cant see it being of any use at all

It's not that bright. Just enough so you put your ashes in the ashtray and don't stab them into the dash pad or miss and drop them all over the carpet.

Originally Posted by tucsonjwt

I checked resistance at the fuel sending units (supply terminal to ground terminal and tank) - result was 102 ohms on a full tank. I cleaned ground connection to frame and cleaned off the ground connection on the sending units - no change.
Could the floats on the sending units be damaged and not rising to the top - which is why I only get 1/4 tank readings but have resistance in the units, indicating electrical continuity in the circuit?
The fuel gauge does move slightly when I switch from one tank to the other, and the gauge goes to full when I remove the power supply wire from one tank, so I wonder if this means the gauge is O.K.?

Based on what you've written, it sounds like the gage is good. An open circuit (removing the "power wire" (should be pink/white or pink/black)) is high resistance and should peg the fuel gage high. If that's the case it is logical that the fuel sender has failed.

It still is really odd that both fuel tank senders failed, in the same way, at the same time. What was in that fuel cleaner?

[kris's66lwb]

cool thanks much

[tucsonjwt]

It was gumout All-In-One. On sale at AutoZone for 2/$5. I guess it was not such a bargain after all.
http://www.gumout.com/ourProducts/all-In-OneFSC.asp
The engine was running rough - I think from varnish in the carb/fuel tanks because I was only driving it once or twice a month, and only on short city trips. This is a 454 which is notorious for being "cold blooded" on start up anyway. I sprayed a big can of carb cleaner into the carb while working the throttle, then used the fuel cleaner in the tanks. This gumout really did the trick - poured it in the near empty tanks, filled up, ran it on the highway up to about 55 mph for 10 minutes, ran like new after that.
Maybe that super concentrated solution at the bottom of the tanks cooked what was left of the floats before it got diluted with a full tank.
Note to self and others: Disregard instructions on bottle - next time add to full tank so the cleaner can dilute right away.