1971 Bus - The Great Fuel Gauge Sender Wire Hunt

[JLT]

The subject line says it all, but a little background might be in order. Please bear with me, as this is a long and sordid tale.

The patient is a '71 Transporter whose wiring was heavily "modefiled" by Previous Owner (hereinafter called "PO"). The fuel gauge was stuck eternally on 5/8" full, regardless of the fuel level in the tank.

I pull the instrument panel out of the dash. Tacked onto the back of the fuel gauge is a vibrator. (Why a vibrator on a '71? Good question. Does anybody have a good answer? The only reason I could think of was that PO had replaced the '71 gauge and sender with a post-'72 one, for reasons I can't fathom.)

The vibrator has two input terminals: one is marked "12v" and the other "to gauge" as well as a ground wire. The vibrator's output terminal was plugged into the "+" terminal on the instrument panel housing, to which was connected the brown wire of the gauge itself. The "G" terminal on the housing was completely missing, and the white gauge wire that was supposed to be connected to it was .... grounded to the housing.

I don't know what's going on here. I thought that the "G" terminal and white wire were supposed to go to the sending unit in the tank. So I go back and look at all the connections I undid, which I carefully labeled as to where they went on the cluster. I could find no sender wire whatsoever. (It turns out that the wire marked "to gauge" actually was a switched 12v lead going to the fuse block.) No other wires were unaccounted for except one thin brown wire marked "not ground not 12v" by PO. It disappeared behind the inner front panel of the bus. When hooked to an ohmmeter grounded to the chassis, it registered infinite ohms. I took that to mean that if this is indeed the missing sender wire, there is either a break in the wire between it and the sender or that the sender itself is shot and is creating an open circuit.

So, I says, If I want to confirm that it's a sender wire, all I have to do is find the other end of it and see where the break might be. Well, I can't find the other end. I know that the sender is inside the tank itself, which is tucked behind the engine, and the wire must exit the tank compartment somewhere, but I can't see where. Also, the wiring chart shows a connector between the gauge and the sending unit (marked "T1" on the chart), but I can't find that, either. Is it inside the tank compartment or somewhere between there and the front of the bus? What is the actual path of the sender wire as it goes between the sender and the gauge?

I really don't want to take the engine and tank out at this point, but I'm baffled. If I knew that the T1 connector was outside the tank compartment, I'd be willing to cut an access hole to remove the sender and simply replace that segment of the wire along with the sender, if I had to.

This situation has left me quite confused and PO'd (PO not meaning Previous Owner). Any insight into where that damn wire goes would be gratefully appreciated.

[dtrumbo]

You can barely see in this picture (please excuse the dirt, this was BEFORE I cleaned!) a brown wire coming out of the 'gray wall' just to the left of the grommet that passes through the firewall (circled). You can click on it to make it a little bigger.



This is the sender wire. The 'T1' connector you speak of is just prior to the wire going behind the wall. Unfortunately, I doubt you'll be able to access it with the engine in the way.

The other thing is, assuming your sending unit is correct for a '71, I doubt a later-bay gauge (one with a vibrator) would work with it. For reference, here's a great article that explains how each style works.

http://www.nls.net/mp/volks/htm/fuel_ga.htm

Scroll down to the part that discusses 'balanced coil' senders. This is the type that is supposed to be in your bus.

If you decide to restore your fuel gauge to it's original configuration, I highly recommend giving Ken Madsen at www.thebusco.com a try. I bought a very nice complete instrument panel from him for my '70 at a very reasonable price.

Good luck and happy spelunking!

[JLT]

You can barely see in this picture (please excuse the dirt, this was BEFORE I cleaned!) a brown wire coming out of the 'gray wall' just to the left of the grommet that passes through the firewall (circled).

I don't see that wire at all in my bus, although the grommet (with the wiring harness that goes from the starter solenoid to the battery) is easy to spot. Is that wire in front of the engine flange when the engine is installed? (I also looked pretty hard at the whole area around the starter, when I was under the bus, but couldn't find a wire -- brown or otherwise -- anywhere around it.

The other thing is, assuming your sending unit is correct for a '71, I doubt a later-bay gauge (one with a vibrator) would work with it. For reference, here's a great article that explains how each style works.

http://www.nls.net/mp/volks/htm/fuel_ga.htm

Scroll down to the part that discusses 'balanced coil' senders. This is the type that is supposed to be in your bus.

Yes, I saw that page. That's where I got the idea of testing the sender in situ by seeing if there was any resistance at all from that mystery brown wire to the chassis. And the schematic of the fuel gauge raises another point: It shows three connections ... hot (6 v in the picture but 12 in my bus, of course), sender lead, and ground. There are only two terminals on the gauge itself, the "+" terminal and the "G" terminal. Am I correct in assuming that the ground is provided by the metal-to-metal contact with the instrument cluster housing?

Which reminds me: The Bentley book gives a procedure for using a battery and voltmeter to test continuity in the sender. I tried that, too. Somebody somewhere said that these tests have to be done when the float is actually immersed in gasoline, so I tried that, too. Same result.

I just KNEW this wasn't going to be easy ....

[dtrumbo]

Is that wire in front of the engine flange when the engine is installed?

I believe so. I know I never saw that wire in my bus until I removed the engine, even though I had replaced the battery-to-starter cable. The sender wire doesn't pass through the same grommet as the battery cable, but another one less conspicuous. I think it's the same one that the oil pressure sender and generator wire pass though as well. They all end up in a common sleeve that goes up front which is why you don't find the brown wire all by itself under the bus.

Am I correct in assuming that the ground is provided by the metal-to-metal contact with the instrument cluster housing?

Yes, the gauge grounds to the metal back of the instrument cluster which is then grounded by a brown wire to the chassis. Take a look:



At the top-center of the diagram is the instrument cluster (K). The thin black lines are the ground "wires" which are really the metal of the backing plate. At the top of the cluster is where the ground connection is made. On your actual instrument cluster it's a circular arrangement of spade lugs which look similar to a crown. One of the brown wires goes to the chassis and the other wires go to other things that need a ground connection.

I just KNEW this wasn't going to be easy ....

That just makes the victory sweeter! Keep at it!

[JLT]

That just makes the victory sweeter! Keep at it!

I don't know about sweet ... it's more like "no more sour."

Anyway, I have achieved gauge-ness. I never could find out where the wire came out of the fuel tank compartment ... in fact, there is a very good chance that it never did, but was removed by PO at some point.

What I ended up doing was (forgive me, Colin, for I have sinned) cut a hole in the rear deck of the bus to access the top of the fuel tank and sender. I then ran another wire from the sender to the gauge and repaired the hole with a home-made removable plate (I figure that if the sender goes bad, that work will not have been in vain).

I hooked up everything, reconnected the battery, switched the ignition on and the gauge read half full. I went to the gas station, put 7.2 gallons in, and now it reads almost full (like 7/8 of a tank). So I might just have a working gauge again.

PO also disconnected the clock for some reason. Once I found the connection and plugged it back in, it now works, too. This may be the first bus I've ever owned that had a working VW clock.

[Amskeptic]

What I ended up doing was (forgive me, Colin, for I have sinned) cut a hole in the rear deck of the bus to access the top of the fuel tank and sender. I then ran another wire from the sender to the gauge and repaired the hole with a home-made removable plate (I figure that if the sender goes bad, that work will not have been in vain).

Ouch sayeth the VW gods on high in Wolfsburg Heaven. . .

That sender wire connector on my bus is visible under the car near the right rear shock absorber area at the frame rail. Type 4 in my case, but I don't ever remember seeing it where it is on yours, dtrumbo. . .
Colin

[JLT]

Ouch sayeth the VW gods on high in Wolfsburg Heaven. . .

I am now saying "Fahre nur mit Shiebetur verriegelt!" seventy times in penance.

That sender wire connector on my bus is visible under the car near the right rear shock absorber area at the frame rail. Type 4 in my case, but I don't ever remember seeing it where it is on yours, dtrumbo. . .

I looked for it there on my '71 and couldn't see it at all.

And I spoke too soon about the clock. It works intermittently, even though it seems to have current all the time. It probably needs to be taken out and given a good clean. (Speaking of Shiebeturen, after having had a lot of trouble getting the sliding door open, I eventually took the rear locking mechanism off and found that the grease had congealed to the texture of paraffin wax over thirty-eight years. I took it to the Kombi Haus where Justin put it into their degreaser. When I got it back, I put in new lithium grease and reinstalled the mechanism, and now the door leaps open when I turn the handle.) Moral: Don't assume that a mechanical assembly has failed before you clean it off and lube it.

[JLT]

Am I correct in assuming that the ground is provided by the metal-to-metal contact with the instrument cluster housing?

Yes, the gauge grounds to the metal back of the instrument cluster which is then grounded by a brown wire to the chassis. Take a look:



At the top-center of the diagram is the instrument cluster (K). The thin black lines are the ground "wires" which are really the metal of the backing plate. At the top of the cluster is where the ground connection is made. On your actual instrument cluster it's a circular arrangement of spade lugs which look similar to a crown. One of the brown wires goes to the chassis and the other wires go to other things that need a ground connection.

On reading this several years later, I realized that there were a few things that weren't clear. First, the "G" on the back of the instrument cluster at the fuel gauge leads goes to the fuel sensor in the tank, not the ground to the vehicle. This is because it's the resistance to the ground connection that's actually being measured. The "+" connection goes to that same network of wires that connect the bulbs for the oil pressure sensor, the alternator/generator charge, and so on. These are actually all "hot" terminals, energized when you turn on the ignition. That's why you see them go on in the "test" mode when you turn the key. As the car starts, those lights go off because the grounds are interrupted by either the oil pressure switch turning off as the oil system is pressurized or the alternator/generator ground being overridden by whatever controls the voltage in the system.

I think that I'm clarifying the situation, not muddying it.