[TR] Troubleshooting TR3A fuel gauge

[Dave MacKay]

On 30 May, Bill Beech <wbeech at flash.net> wrote:

>Dave,

>Be sure the gauge body is grounded.  Check resistance at the sender with
wires off, with wires connected you should see the gauge moving.

>Good luck,

>Bill

>

>Sent from my DynaTAC 8000X

>

>On May 29, 2019, at 11:38 PM, Dave MacKay <mailto:dave at mdmackay.ca> wrote:

>Thanks Bill.

>

>I should've thought of connecting 12v directly to the B post of the gauge.
I'll try that to see if it makes a difference. I'll also try putting 12v to
the T post of the gauge (the side going to the sender unit) to see if I get
a steady resistance (ohms).

>

>I'm happy for your help.

>

>Thank-you,

>

>Dave

>

>On Thu, May 30, 2019, 12:10 AM mailto:Wbeech at flash.net, <mailto:
wbeech at flash.net> wrote:

>Barney at http://Mgaguru.com is a good guy that knows his stuff.   Ohms
should roughly go from 10-90(Barney says 0-70) with the clothes hanger and
all wires disconnected.

>

>Check all your related connections, the sender and the gauge need to be
grounded

>

>I would expect 12v at the hot post of the gauge.  If your not getting it
try a direct jumper and test the system.   New gauges are NLA but you can
either find them on eBay or other parts sites, or send your gauge AND
sender to one of the several reputable >instrument rebuilders.

>

>Bill B

>TS30800L

>Sent from my DynaTAC 8000X

>

>On May 29, 2019, at 10:29 PM, Dave MacKay <mailto:dave at mdmackay.ca> wrote:

>Hello:

>I’ve been troubleshooting the fuel gauge on my TR3A because it has not
been providing an accurate indication (or even a reasonable approximation)
of the fuel level in my tank.

>I referred to a number of documents and old posts about how to
troubleshoot and calibrate the fuel gauge and sending unit (e.g.,
https://www.triumphexp.com/forum/tr2-and-tr3-forum.6/faulty-fuel-gauge-57-tr-3.1244960/
and >http://mgaguru.com/mgtech/electric/fg_01htm).

>I started by looping a clothes hanger around the float in the tank and
reading how many ohms I saw at different levels. What I found was that the
reading fluctuated --- it didn’t stay the same even when I held the float
at one level. I then checked to ensure >that the grounds were good (they
were). Before concluding that the sending unit was flakey, I thought I’d
better ensure that I was getting good power to the unit.

>That’s where things got weird.

>-       I read 7.6V between the sending unit and ground.

>-       I read 7.65V between the T terminal of the fuel gauge (which
connects to the fuel tank sending unit) and ground. However, this reading
was erratic; the value would change to, say 4V.

>-       I read 10.6V at the B terminal of the fuel gauge

>-       I read 10.9V at the A4 terminal of the fuse box.

>-       I read 11.9V at the A2 terminal of the fuse box.

>-       I read 12.5v between the terminals of the battery.

>I’m a bit baffled. I expected that I’d see about 12V at all points. Even
if the fuel gauge was bad, I would have expected to see the same voltage at
the battery, A2, A4, and the B terminal of the gauge. As it is, I’m seeing
a drop of about 2V among them.

>What might be causing the voltage drops that I’m seeing? Could it be as
simple as a broken fuel gauge? If so, how could I test that?

>Moss lists the fuel gauge as NLA. Does anyone know of another source?

>BTW, when I switched my generator for an alternator years ago, I
eliminated the control box (regulator).

>Thanks in advance.

>Dave MacKay

>TR3A s/n 68639L

>near Toronto, Canada



Thanks Bill.



The gauge is grounded via the holder with the knurled nut. It reads good. I
hooked up a separate ground wire but it didn’t make a difference so that I
felt confident the ground was good.



When you said to check resistance at the sender with wires off, did you
mean power off (e.g., battery disconnected) or to physically disconnect
both wires? I had thought that as long as the power was off I could just
hook up my multimeter and measure the resistance as I moved the float.



Dave
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