Which wire is for the fuel sending a unit?

[Vwbuschris]

I have a 76 Westfalia and trying to figure out what wire is for the sending unit. Does anyone have any advice?

[busdaddy]

None of those, the tank sender wire is found inboard of the RR shock absorber on 72+ models, it goes up into the tank area through the floor on the angled area near the side. It's the brown one when you do locate it.
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[Vwbuschris]

Thanks for the help

[jtauxe]

Funny, that... I just uploaded a photo of the fuel sending unit wire with its T-connector and grommet through the floor. It feeds into the wiring harness under there, near the starter.

Mind you, that is for a truck, and our fuel tanks are located forward, on the floor, as it were.
The fuel tank in a kombi would sit in the depression next to the T-connector.
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1969 Transporter, 1971 Westfalia, 1976, 1977, 1976, 1977, 1971, 1973, 1977 Westfalias,
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[75 Westy FI noob]

I love this site so flippin' much. Thanks guys.

i verified my gauge works.. i can tell someone has replaced the sending unit before (the sheet metal above it is cut in H pattern).. hoping to find/fix a wiring problem.

[NASkeet]

[75 Westy FI noob]

Moved on to the sending unit …

If I jump from battery to FSU ground wire.. i get 12.4 V
So ground is good.

If I jump FSU ground wire to FSU hot wire… Gauge goes to 1/1 Full.
So that implies the hot line is also good.

But, if i put a meter between the hot and ground in the FSU area (pictured) … the voltage dances all around between 2.5 and 4.5 V. I expected to see 12.

Is that normal or do I have a bad hot wire into the FSU after all ?

Running a line from battery to FSU hot input does not move the guage.

Btw, do you think i can squeeze a new one into that opening? Its hing style 1975.

[busdaddy]

Don't go putting 12v into any of those wires!

If grounding the sender wire gets a full tank the gauge and wire are good, the sender grounds that wire gradually as fuel level increases, if the tank is empty it should read ~90 ohms.
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[75 Westy FI noob]

Thanks BD.. i thought every thing could handle 12. lol
Thanks for the word on the timing also.

I guess it’s a bad FSU. Wishful thinking that it would be wiring.

Hopefully i can shoehorn a new one in there.
I tried to order a new one yesterday but the vw man convinced me to test ground first.

[mikedjames]

The voltage regulator on the fuel guage contains a bimetallic strip and heater. It pulses the 12 volts on and off a few times a second, heating up the strip when the output voltage is 12 volts, breaking the contact when the strip gets hot enough.
It produces a voltage which averages about 5 volts.

With a digital meter it presents values that dance about because the meter averages the voltage about 3 times a second, the regulator pulses a couple of times a second, the two beat together and produce junk.

If you connect an analog meter or an oscilloscope you would see the voltage swing to 12 volts and back again.

If the fuel gauge is working, and you have a pulsing voltage at the sender end of the wire, the sender may just have partly burnt out.

They all burn out eventually, cheap reproduction senders are worse than cheap reproductions made 10 years ago which are worse than originals.

They all read tank level and produce different values for different amounts of fuel, just the calibration of the newer senders is very poor.

On my current sender, the tank goes into the red sector after 100 miles.
After another 100 miles, it sits a needle's width off empty. After another 50 miles it sits at empty and it is empty.

If you hunt around you may find a sender with approximately the correct construction (the winding of the resistance wire is bunched with tighter turns up at one end) - these will cost more.
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[Wildthings]

I would cut off most of your flap and make a decent air tight cover for it. Leave enough of the flap so that it gets up onto the flat and then increase the size of the hole towards the rear of the body a bit. It didn't take me too long to make the fitted cover I have, but you could also use a flat cover and some fire stop caulk.

This is the cover I made for my 77, but I would move the entire hole rearward 3/4-1" if I was doing it again, so I didn't have to deal with the bend in the deck.

[75 Westy FI noob]

[75 Westy FI noob]

[75 Westy FI noob]

[75 Westy FI noob]

I put my new FSU in today. Old one looked very rough, i think it has barnacles!
May still try to clean it. Lol

Wondering if there’s a trick to tightening the new one. Tapped it h a punch but still needs 1/8 turn to finish.

[busdaddy]

Grease the O ring as well as the bayonet tabs.
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[75 Westy FI noob]

Nevemind.. got it sorted out!

Pliers are from an electrical pinch kit. Worked great

[busdaddy]

If the rest of the inside of your tank looks anything close to that you have much bigger issues in your future than just not being able to tell how much gas you have.
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[NASkeet]

[75 Westy FI noob]

I always ran 'real gas' in there ... but I left the bus with some family for a few years. They put new gas in it.. then parked it and it sat for about 8 years.

I assumed that was a newish FSU... but obviously it isnt very new at all.

exterior of the tank looks good. I didn't shine a light into the tank. maybe i should have a look in there. i was trying to switch them quickly and didn't think to look in there.

I am afraid I may have over tightened the FSU ...it seemed to need another 1/8 turn.. and I used those pliers and put torque on it.. it didn't move, then suddenly popped forward into hopefully the lock position. so it's good, or i broke it.

guage on the dash is working now tho!