[T3] fuel gauge and gauge light fluctuating

David Yaghoubian goob at roadrunner.com
Sun Sep 21 13:03:53 PDT 2014


Some important things to quickly add:

I just went down and found my old gauge (the original gauge, my family is
original owner on this T3) and in the process realized that I have an extra
lamp base with a #31 lead... which I pulled off the 71 gauge and put on my
old gauge for storage. So in case a #31 ground is the solution, I have a
lamp base ready.

I then installed the old gauge to the original lamp base, and the condition
was exactly the same. Hence, I am ruling out the year difference in the
gauges, or the gauge itself. 

The issue with the lights seems like it will be cured once I obtain a soild
gauge body ground, but no matter how I try to ground the body I can't seem
to get the fuel gauge to rad anywhere near accurately. It maxes out with the
bright lights on sometimes, and/or when the gauge is moved (which then cuts
the gauge lights). 

That's where I'm at.  Anyone want to venture a sane plan of attack?

-----Original Message-----
From: type3-vwtype3.org [mailto:type3-vwtype3.org-bounces at lists.vwtype3.org]
On Behalf Of David Yaghoubian
Sent: Sunday, September 21, 2014 12:38 PM
To: type3 at vwtype3.org
Subject: Re: [T3] fuel gauge and gauge light fluctuating

Quick addendum. I meant to say I AM ruling those posts out (!). 

-----Original Message-----
From: David Yaghoubian [mailto:goob at roadrunner.com]
Sent: Sunday, September 21, 2014 12:35 PM
To: 'type3 at vwtype3.org'
Subject: RE: [T3] fuel gauge and gauge light fluctuating

Tremendous. Thanks Jim and Keith for the responses.

So to start, I pulled the gauge back out and confirmed that my lamp base
(which I was calling a harness for lack of appropriate term) does NOT have
the #31 ground tab on the back. I think it is perhaps important to mention
now that I installed a '71 gauge set when I did the dash in 2006 (to get the
trip odo primarily) so I am running a 71 gauge without a #31 ground. Again,
this hasn't been an issue up until last night (although I don't know if this
has to do with why I can't get the gauge to seat fully) but it might be
relevant. I took a few photos of the back of the lamp base in case anyone is
interested in seeing this ultra-rare T3 item. ;)

I then used a tiny flathead screwdriver to gently bend the ends of the three
contact post push-on so they fit tighter. I noticed the lamp base seemed to
seat more solidly when I put it back on, but the condition was the same when
I tried the lights and ignition again, so I am not ruling those posts out.

Right now, if I push slightly on the left rim of the gauge, the lights come
on full in the gauge but the fuel gauge needle reads dead empty. When I
release pressure from that edge, move the gauge a bit, or tap the dash just
above it, the fuel needle taps out, and the lights go off completely. This,
of course, suggests a problem with the gauge body ground, but I am stumped
as to why a bare ground wire to the body seems to have no effect whatsoever.
The gauge body seems completely corrosion free, but I will take some steel
wool to a portion and see if that makes a difference.

Regarding adding a #31 wire myself, I will go back out and take a look at
the wires joined to the socket just below the hole where the black wire
comes in (those would all be grounds, correct?) and see if that is something
I think I can handle without melting anything. If not, perhaps I can
purchase one of your extras Jim?
	
In absence of a #31 wire for now, is there a way to definitively tell if
this is a ground issue at the housing before getting into the soldering or
swapping out what was a perfectly functioning lamp base? Would adding a #31
wire eliminate the need for the gauge housing ground as the dash (thus
making it unnecessary for me to figure out how to finally seat this darn
thing?).

Thanks again,

Dave



-----Original Message-----
From: type3-vwtype3.org [mailto:type3-vwtype3.org-bounces at lists.vwtype3.org]
On Behalf Of Jim Adney
Sent: Sunday, September 21, 2014 10:25 AM
To: type3 at vwtype3.org
Subject: Re: [T3] fuel gauge and gauge light fluctuating

Jim wrote:


This is a fairly common problem. I THINK the problem is due to the fact that
up thru '68 the gauge gets it's ground via the springs that retain it in the
dash, but that seems to be at odds with some of your observations. I've
never seen a problem with the 3 contact posts; those are always pretty
tight, but I can see now that this is a possibility.  

I think this problem arises after many years as the vinyl dashboard pad
shrinks and loosens the gauge units. It can be compounded by people pushing
the retainer springs out PAST the humps in the metal dash, which actually
makes them looser. Starting in '69, the speedo and clock bodies got their
own dedicated ground wires, but the left gauge body never did. Looking at
the lamp bases I have here, they all have a #31 (ground) faston tab on the
back just below the hole where the black wire exits. On my later cars, that
tab gets a ground wire.

Does that #31 tab exist on your '68 lamp base? If not, you could either
solder in a brown ground wire next to the black power wire, or swap in a
later lamp base (I have several) that has that ground tab, and make a brown
ground wire to ground that tab. If you want to solder in a new ground wire,
just slip it in next to the black wire and solder it with the other wires
that are joined to the socket just below the hole where the black wire comes
in.

All the lamp bases I've found in my pile of gauge parts have this #31 ground
tab, but it's quite possible that I don't have any early ones. 
Looking at the parts list, I see that only one lamp base is listed, and that
is a B version which is listed for all years. That means there were 2
previous versions, so it seems likely that a non-grounded version existed. I
don't know what other version there might have been, but people who know the
really early cars may know.

I suspect that your attempts to run a separate ground wire were stymied by
corrosion on the housing, making good contact iffy. But I'm always puzzled
when this question comes up. I've seen this problem in later cars, where the
ground wire should be there. I just checked my '71 and it seems to have a
wire of some kind, presumably a ground, attached to that tab. Any yet I've
had other '71s display the same problem that you have. Maybe you're right
that the problem is with the center ground pin between the metal housing and
the lamp base.  

One of the common symptoms is that if you turn on the 4-way flashers with
the key off, the gas gauge needle bangs from limit to limit. Do you see
this? This all seems to get cured by tapping/moving the instrument. Maybe
the rivet under that ground tab loses contact. That seems unlikely, however,
since I don't see similar problems with the other rivets. Or maybe there's a
problem at the other end of my ground wires.  

Let me know if your '68 has that #31 tab. This comes up often enough that we
really should try to get to the root cause of it.  

--
*******************************
Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
*******************************

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