Tan wire to fuel tank sender

[72bowtiestepper]

I searched the forum for fuel gauge problems and could not find a answer to this question...What voltage should show on a voltmeter when touching the tan wire that connects to the fuel tank sender ??
Mine shows 8 1/2 volts with ignition on & engine running and touching the tan wire and to ground.
I also read it should NOT show full 12 volts...Is 8 1/2 volts safe ??
Don't want any surprise gas tank explosions !!

[Big Kev-O]

It isn't the voltage that is a danger it is the current. The resistor inside the sending unit can get hot if it receives full current from the battery. The current through the sending unit is limited by the gauge resister in combination with the sending unit's resistance.

Are you measuring 8.5V with the tan wire connected to the sending unit?

How may ohms do you read across the ground tab and sending unit connector with the wires unplugged?

How many ohms do you read across the resistor on the back of the gauge?

What position is the gauge needle in,
with ignition on:
with ignition off:
with sending unit wire disconnected:

[72bowtiestepper]

Originally Posted by Big Kev-O

It isn't the voltage that is a danger it is the current. The resistor inside the sending unit can get hot if it receives full current from the battery. The current through the sending unit is limited by the gauge resister in combination with the sending unit's resistance.

Are you measuring 8.5V with the tan wire connected to the sending unit?

How may ohms do you read across the ground tab and sending unit connector with the wires unplugged?

How many ohms do you read across the resistor on the back of the gauge?

What position is the gauge needle in,
with ignition on:
with ignition off:
with sending unit wire disconnected:

Thanks for responding Big Kev o
Will check later tonight with my ohm meter....with sending unit wire disconnected the gauge is in the 3 o'clock position.

[HO455]

TBONE1964'S excellent fuel guage guide may help you.

https://67-72chevytrucks.com/vboard/...d.php?t=640615

[HO455]

I wouldn't worry too much about the fuel guage causing a gas tank explosion. The system is inherently safe. Even when shade tree mechanics who listened to their drunk, claims to be an electrical genius, buddy try to rewire them they still don't explode.
I have literally been in and around thousands of trucks in wrecking yards over the last 45 years or so and I have yet to see a truck (or car) with an exploded gas tank.
Not to say it isn't possible if someone really tried hard but, most of those folks work in Hollywood.

[Wizo]

TBONE1964'S your go to man. Please consult with him before you go any further.

[Big Kev-O]

Originally Posted by 72bowtiestepper

Thanks for responding Big Kev o
Will check later tonight with my ohm meter....with sending unit wire disconnected the gauge is in the 3 o'clock position.

That is normal. I suspect you may have a faulty fuel sending unit. If you ground the sending unit wire at the tank your fuel gauge should read empty. If it does read empty this confirms your gauge is good & your sending unit has gone bad. Ground the sending unit wire at the tank and report back.

[72bowtiestepper]

Originally Posted by Big Kev-O

That is normal. I suspect you may have a faulty fuel sending unit. If you ground the sending unit wire at the tank your fuel gauge should read empty. If it does read empty this confirms your gauge is good & your sending unit has gone bad. Ground the sending unit wire at the tank and report back.

OK....I got to check before going to work the following :

Grounding the tan wire with power on did make the gauge show empty.

The sending unit (new) in tank that is nearly full showed 88ohms.

The tan sending unit wire from gauge disconnected showed 36ohms with power off.

I will try to see if the gauge works like it should tomorrow with the truck out of the garage (Just in case ! ) Thanks to all that responded...I like to double check for safety anything electric...This truck was a long project...don't want any fires or other mishaps !

[72bowtiestepper]

Gauge working as it should...Thanks again to all that chimed in !