You can't use the volt/ohm meter to verify the gauge, but you can use
it to verify the sending unit.
1. Disconnect the wire from the terminal on the tank's sending unit.
2. Connect the meter between the terminal on the tank's sending
unit and a GOOD ground (clean with a little sandpaper) on the tank.
3. Set the meter to a low ohms scale. The TF trucks read around 30
ohms when "full" and near zero ohms empty. If the reading is wrong
fix or replace the sending unit. In mine, the brass strap that
connected the actual variable resistor at the bottom of the sending
unit to the terminal on the outside of the sending unit was broken
and was easily repaired with 100 watt soldering gun.
If step 3 checks out good, you can figure out where the wiring is going
wrong by making a test rig that consists of a length of 18 gauge wire
attached to an alligator clip on one side of a 15 ohm resistor with
another length of wire attached to a sharp pointed device (I used a
large paper clip and ground a point on it). Exactly 15 ohms is not
important, 10 to 20 will do.
4. Disconnect the gas gauge wire where it attaches to the tank.
5. Hook the alligator clip to a good ground in the truck.
6. Turn on the key, but you shouldn't have to start the engine.
7. Touch the pointed end of the test rig to the gas gauge terminal
that goes to the gas tank. If the gauge reads still reads
full, the problem is in the gauge, the grounding of the gauge
or the power circuit supplying the gauge. If the gauge reads
around half full (or half empty if you are a pessimist) continue
probing the gas gauge wire as it makes it's way towards the tank.
When you reach a point that the gauge no longer reads half full
as you probe the wire you have gone past the open (break) in
the wire.
-----Original Message-----
From: Hudson29@aol.com [mailto:Hudson29@aol.com]
Sent: Saturday, June 26, 1999 7:19 PM
To: oletrucks@autox.team.net
Subject: [oletrucks] How Do You Test a Gas Gauge Sending Unit?
I just got the gas tank back from Mattson's Radiator after having
the
ReNew process done and decided to "bench" test the new sending unit
purchased
during my brief flirtation with Golden State Pickup Parts.
The simplest way to do this I figured, would be to go out to the
truck, wire the sending unit up to the harness and power the system up
(fresh
6v Optima) watching the gauge while moving the float by hand. The gauge
should read "empty" with the float dangling and it should climb to "full"
when the float is moved up. Wiring in the new sending unit makes no
difference to the gauge reading.
Putting theory to practice confirms that something is fouled up
someplace. Even with the float fully down the needle rises to "full."
Alternately removing the ground and restoring it get the needle to make a
very slight wiggle, but alas, no movement. Touching the wires together does
not change the gauge reading either. The gauge normally rests on "empty" and
goes to "full" with the key "on" even with the tank empty.
If I could verify the sending unit is not at fault, I could go ahead
and install it and get the tank in. I have an old Radio Shack volt/ohm
meter.
Can I use this to verify the gauge? Am I condemned, like poor Smokey, to
wander the highways and byways of America with no working gas gauge, spare
gas cans always along for the ride?
Paul O'Neil, Hudson29@aol.com
1951 Chevrolet 3600 Pickup Project, See it at:
The Poor Man's Advanced Design Tech Tips Page
http://home.earthlink.net/~conntest47/
Fullerton, California USA
AEROMARK - Need Rubber Stamps or Signs? See:
http://hometown.aol.com/hudson29/myhomepage/index.html
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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