New Wiring Harness=Fuel Gauge Issue

[Bare64]

Evening Guys, need a little guidance. Read through 5-6 threads trying to find out if any of you have had this issue. Installed a brand new American Autowire harness from LMC.

What I know: Tan wire Ohms out, no breaks, continuity
Harness was plug and play at gauge


Son removed brand new fuel sending unit stealing gas (he's 29 years old and an idiot. Nut on sending unit underneath the eyelet where Tan wire attaches spins in both directions, could it have gotten broken when he removed the sending unit?


Ignition off gauge reads about right 1/4 tank, I put 5 gallons of gas in it.


Ignition on it slams immediately to E.


Any help much appreciated, a few photos for reference:

[1966shortwide]

I think that attache's to flat strap. Just take it out and you will see the problem .That bottom nut should be solid. He might have twisted it off. You can probably solder it back together , and you can check unit out of the tank. turn key on and move float up and down and it should do react the same.Just be sure to ground as if in the tank. up is full, down is empty

[jtrichard]

sounds like it is shorted/grounded in side on the tank unit pull the wire off then turn key on and see what happens if nothing then touch the tan wire to ground and see if it slams to E again if so pull the sending unit and see if you can repair it... send pics of coarse

[Bare64]

Thanks, appreciate the quick responses and suggestions

[Bare64]

Hummmmmmm.......Fuel Sending Unit flat strap was twisted but not broken. Ohm'ed at .6 in empty position, 34.7 in full position. Think I read here that it should ohm out at 0-90? Pink wire is on drivers side at gauge, tan on passenger side just like the new harness came, is this correct? Tan wire has continuity between gauge and unit also.

[Bare64]

it is ok if the fuel sending unit is grounded like so, right?

[TBONE1964]

Originally Posted by Bare64

Hummmmmmm.......Fuel Sending Unit flat strap was twisted but not broken. Ohm'ed at .6 in empty position, 34.7 in full position. Think I read here that it should ohm out at 0-90? Pink wire is on drivers side at gauge, tan on passenger side just like the new harness came, is this correct? Tan wire has continuity between gauge and unit also.

For a 1964, the ohm reading you took is correct. These only have a 0 - 30 ohm scale. It was not until 1965 that they changed to a 0-90 ohm scale and I am not 100% sure this applied to trucks as the gauges are all the same from 64-66.

How does your temp gauge work? The fuel gauge and temp gauge share the same power with the pink wire and should have 12V with the key on. The tan wire should run from the tank to the fuse panel and then to the gauge.

Hope this helps. Make sure you have voltage when (ignition on/off) and where it needs to be on the pink wire.

Tom

[jtrichard]

with sender (tan) wire off what does the gauge do when you turn on the key?

[1966shortwide]

As before I suggested you leave the sender out of the tank, with all wire's still connected and ground also. move the float up and down , turn key to on , don't have to have engine running and watch the gas gage and see if it respond's to what you are doing with the float arm .Also with a ohm's tester you can watch ohm's reading from o to 30 in order and 30 to 0 in order. example ===== 0 1,2,3,4,5,6,7,8,9,10,,11,and all the way to 30 . the bad sender will do this========0,1,2,,3,4,5,6,7,8,9,8,7,6,10,11,12,13,10,14,15,12,. another word's a good sender will climb number's up or down in order.Hope this help's.

[Bare64]

TBone - No clue, have not ran the motor enough to tell if the Temperature Gauge is working, Oil Pressure and Volt Meter are working though but they are all aftermarket.

jt - no clue, did not check that due to battery going dead and jumper cables missing.

Shortwide - that is exactly how it ohm'ed out. I checked the VM at 1/4~9ohm, 1/2~18ohms and 3/4~27ohms guesstimates. Wires weren't connected though, will follow up with wires connected.

Will follow up with you guys once I get back in town. Thanks for the responses

[Bare64]

Originally Posted by jtrichard

with sender (tan) wire off what does the gauge do when you turn on the key?

Tan wire off, truck off......gauge reads correct
Tan wire on in accessory position.......gauge goes dead empty
Tan wire on, truck running.......dead empty
Tan wire on, restart truck.....100% full

[Bare64]

Attached to sending unit, accessory position......."0" volts


Attached to tan wire, accessory position........"12" volts


Broken sending unit?

Thanks

[65 C20]

Originally Posted by Bare64

Tan wire off, truck off......gauge reads correct
Tan wire on in accessory position.......gauge goes dead empty
Tan wire on, truck running.......dead empty
Tan wire on, restart truck.....100% full

I don't know much about fuel gauges but there is no accessory postion on a stock key.

All the way to left is ignition locked.
Click 1 to right ignition is off but not locked.


Click 1 more time to right ignition is on.
spring loaded last postion to right and that is start mode.

[Bare64]

Originally Posted by 65 C20

I don't know much about fuel gauges but there is no accessory postion on a stock key.

All the way to left is ignition locked.
Click 1 to right ignition is off but not locked.


Click 1 more time to right ignition is on.
spring loaded last postion to right and that is start mode.

Tilt steering, ignition is on column, guess I should use term "run position"

[jtrichard]

take the wire off then turn key to "run" see what it does ....then with key still on/run ground the wire and see what it does .... gauge should "float" (with wire off ) and "slam" to E when grounded if I remember right... report back

[Bare64]

Originally Posted by jtrichard

take the wire off then turn key to "run" see what it does ....then with key still on/run ground the wire and see what it does .... gauge should "float" (with wire off ) and "slam" to E when grounded if I remember right... report back

Tan wire off, ignition in run the gauge pegs to full. Ground wire it still stays pegged to full.

ground wire to frame, stays pegged

Floats with ignition off, turn on ignition with wire hooked up or not pegs to full, turn off, then ignition on with tan wire hooked it pegs back to empty. Do not have to touch the wire.
Video:

[Bare64]

How harness came:

What Instructions Say:

Gauge is acting right now.........took me long enough
Will update if it gets crazy again.

[Bare64]

Pretty sure this is not suppose to happen either. As soon as it comes back to idle voltage drops something crazy. Bad alternator? As soon as I try to start again, dead as a door nail.
Video:

[Bare64]

New alternator, all good on charging the system. Now to get power to courtesy lights that are at driver and passenger spots and dome lights. Need to buy the switches for the doors to make them come on and off.