• Registered: 2008-11-01
  • Posts: 6

Topic: fuel gauge

On a 72 beetle my fuel gauge doesn't work.  I only have one hookup on sending unit and it is hooked up to fuel gauge.  The wiring diagram shows two wires from the sending unit - one to the gauge and the other to unlabeled hookup on speedo housing.  I'm guessing that is ground and tried connecting to a mounting screw for the sending unit but didn't work.  If I hook up the wire from the fuel gauge to ground and also to sending unit the fuel gauge will register full, so I know the needle isn't stuck.

Does anyone know how to hook up that second wire.  If I was right to hook a ground to the speedo housing and to the sending unit mounting screw could my problem be in the sending unit?

  • From: Vancouver Canada
  • Registered: 2004-04-28
  • Posts: 441

Re: fuel gauge

You don't need a second wire. 
Get your ohm meter and measure the resistance between the flange of the sending unit and the car's body.

  • From: Bethel Park PA
  • Registered: 2004-06-27
  • Posts: 686

Re: fuel gauge

If the fuel tank is properly mounted it's insulated from the car's body by a rubber gasket.  Trying to ground something to the sending unit mounting bolts won't work.

David H
'66 VW Beetle w/sunroof
http://tinyurl.com/qhw59
"Where am I going ... and why am I in this handbasket?"
  • From: Washington, Indiana
  • Registered: 2004-03-27
  • Posts: 1,423

Re: fuel gauge

Steelman, is your bug a super beetle?

                                                           Yancey

Yancey's Website

  • Registered: 2008-11-01
  • Posts: 6

Re: fuel gauge

Yancey,no it's a standard beetle.

David H, I don't think there is a rubber gasket insulating fuel tank from body; does this need to be done?

Bruce, I haven't measured resistance from the sending unit to the body yet.  Is it supposed to be open or grounded because if the fuel tank is supposed to have a rubber gasket it would be open unless I had to ground it.

Again thanks for all of the help.

  • Registered: 2006-07-20
  • Posts: 332

Re: fuel gauge

The screws attaching the sending unit to the gas tank would ground it, even with the rubber gasket, no?

  • From: somewhere over the rainbow USA
  • Registered: 2006-07-26
  • Posts: 1,882

Re: fuel gauge

steelman,
It is correct that the mounting screws ground the sending unit but one must have a metal,usually copper washer, the others have a plastic washer. You can narrow it down to the sending unit or gauge by pulling off the sending unit and grounding that wire with key on. If the gauge goes to full it is the sending unit if not, it is in the gauge,vibrator,and or wiring upstream of sending unit. One thing that happens is that the brass nuts that hold the gauge to the speedo head work loose.

                                                                         burrhead

burrhead

A wise man makes his own decisions, an ignorant man follows public opinion.
  • From: Bethel Park PA
  • Registered: 2004-06-27
  • Posts: 686

Re: fuel gauge

The rubber gasket between the gas tank and the body isn't absolutely necessary.  It's main function is to prevent rubbing and squeaking that you might have with metal to metal contact.   The gasket does provide the effect of insulating the tank from the electrical system.  Since the tank is painted, there is no guarantee of a good ground through the hold-down clamps.  That, plus rust and corrosion at the clamp-to-tank juncture further limits electrical conductivity.  You MAY find a ground at the sender bolts but a good reliable ground can only be somewhere on the body.  And I don't mean on the body like the sheet metal screw that grounds the headlights.  Find a bolt on the chassis and run your grounds to that bolt.  Something like one of the bolts on the front suspension or easier, to one of the ground terminals behind the dash.

Last edited by David H (2009-02-13 14:10:09)

David H
'66 VW Beetle w/sunroof
http://tinyurl.com/qhw59
"Where am I going ... and why am I in this handbasket?"
  • Registered: 2007-03-27
  • Posts: 2,422

Re: fuel gauge

Yeah like to point out here that the ground wires ( usually Brown is part of a Grounding loom !
  In fact the Brown wire grounding loom is actually seperate from the rest of the electrical loom . As in you can start at the Brake light switch un plug it then go to the Emergency hazard switch unplug the loom from the Hazard switch Metal houseing . Then work your way over to the Speedo Body ground then the Speedo Houseing ground , the gauge grounding, Turn Signal Falsher 31 Ground etc. etc.
  Winding up with about a 4 ft long Brown wire'd loom that goes into Y's every 4 - 6 inche's !
  These Y's in the loom are plugged into the Body and Metal Houseing's and #31 prong's on the switche's etc . etc.
  Often I find the E. hazard switch has the back comminig off and Hot wire's in the switch short on the metal houseing, where the grounding loom is grounded !
  This causes problem Thru out the system as the System is grounded in serie's thru this Brown loom too all switches , As well as the Flasher , the fuel gauge vibrator , etc.
   The usuall here is that if the E. Hazard switch is commin apart or the back is loose it causes a short to the metal caseing and Instantly Burn's out the Fuel gauge vibrator that is attached to the back of he Speedo .
  Eventually it will short out the Turn Signal flasher , then the Windsheild wiper switch etc.
  100 Buck's In labour Is the Minimum I charge on under the Dash Short's ! What I tell um straight up ! Cause I know that in order to fix it right ?? I have to at a Minnimum Check the serie's of this Grounding Loom and how / where it's plugged in !
  Usuall here is I find half of this loom if not all of it is Missing with added ground's such as you guy's are suggesting here !
  Usual on this is just too fabricate a new grounding loom altogether and Plug it in, in the proper sequence before I can even start reading the instruction manual on how to operate my New and improved , super Kick Arse Volt Ohm meter , of wich I need to check Switch function and resistance, with !
  Then after 106 page's of proper New and improved, Digital Volt Ohm meter Function and Operation Instruction ! I will find the Bad switch / Relay Etc. I then get to use the New and Improved Phone Book , too look up the part's house Number to call se if they have the Switch !
  But only after I read 3 page's of instruction's on how to use the New and Improved phone Book ! LMFAO
                                           Sean