Hi, Frank -
The gauge operates by sensing resistance in the circuit between the wire to
the gauge T terminal and ground. When the tank is full, there is more
resistance than when the tank is empty. For a BJ8 (and I would assume also
for a BJ7), a full tank should give a reading of around 90 ohms when
measured between the green/black wire that connects to the T terminal, and
ground. When the tank is empty, the resistance should be close to zero.
These measurements check the operation of the sending unit.
The best way to check the gauge itself is to remove it from the car.
Connect a 12V source to the B terminal and the negative post of the source
to the central mounting post of the gauge. This should make the gauge read
FULL. Then connect a wire between the central mounting post and the T
terminal. This should make the gauge read EMPTY. To check the gauge
calibration, make up a couple wires with 90 ohm resistors in them and
connect them to the central mounting post. When the end of a wire with 90
ohms resistance is connected to the T terminal, the gauge should read FULL.
When the ends of BOTH wires are touched to the T terminal together, the
sensed resistance is 1/2 of 90, or 45 ohms. This should make the gauge read
approximately 1/2.
Negative or positive ground does not affect the gauge operation.
Steve Byers
HBJ8L/36666
BJ8 Registry
Havelock, NC USA
-----Original Message-----
From: healeys-bounces@autox.team.net [mailto:healeys-bounces@autox.team.net]
On Behalf Of Frank Edwards
Sent: Sunday, September 12, 2010 8:02 PM
To: healeys@autox.team.net
Subject: [Healeys] BJ7 Fuel gage.
Hello Listers;
I can't get my fuel gage to work. If I put 12 volts on it it goes right to
full. When I ground the Tank terminal it stays at full and I believe that
it
should go to empty. The car has been changed to negative ground but I don't
believe that I've ever seen anything about that effecting the fuel gage.
The
sending unit is new but I know that doesn't mean that it's good. The car
has
been sitting for 20+ years.
Any thoughts on this?
Thanks in advance for your help.
Frank R. Edwards 570-784-4662 logical2@hotmail.com
1962 BJ7
1969 Midget
1961 Bugeye
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