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Mystery Wire in Engine Bay and Fule Filter Question
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Technut27
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Joined: May 18, 2015
Posts: 16
Location: Cleveland
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PostPosted: Mon Jun 25, 2018 9:28 pm    Post subject: Mystery Wire in Engine Bay and Fule Filter Question Reply with quote

Hello friends!

Wrenched all night and nothing beats it Smile

No matter now many times I go through my 74 I always seem to find new mystery wires to no where. While putting new fuel lines on tonight I found a plug loose behind the carb. I didn't find anything unplugged anywhere and tracing it appears to go into the diagnostic plug? I looked at the wiring diagram and nothing jumped out at me. Any thoughts?

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Secondly I finally go the Thing up high enough for me to get to the fuel line under the tank. There has been a crusty filter there since I got the car. I drained the tank and there is no screen inside on the tap and from what I can see the inside of the tank isn't great but I've seen worse online. Is there any use to filter the gas out of the tank before it gets into the lines? Getting to that filter was a serious pain. The filter in that position was really nasty but my guess is it has been there a very long time.

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I've also read that the condition of the sending unit can be a sign of the condition of the tank... Sad But I don't see crud settled in the tank, just some varnish.

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kubelmann
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Joined: April 13, 2003
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PostPosted: Tue Jun 26, 2018 5:06 am    Post subject: Re: Mystery Wire in Engine Bay and Fule Filter Question Reply with quote

The plug is the VW factory diagnostic plug. The wires in your loom that have a colored stripe or dash on the side are generally part of the test system. This was a very early test circuit. It tested correct function of vehicle lights and other yes/no analog functions. PLEASE CHANGE THE DANGEROUS LOCATION OF YOUR FUEL FILTER!! The old school safe fuel filter system includes the brass screen filter in the bottom of the tank. Then a second in-line filter is used. There are two safe placements which are on the unpressurized section of the fuel systems and one super dangerous placement that is placed on the pressure side of the fuel systems (between the carb and the fuel pump. . Safe Position One: In the line that goes from the back of the pan fuel line to the metal feed tube that goes around the cooling shroud (best) or between the fuel feed tube and the fuel pump (Always filter on the unpressurized size). A failed fuel filter on the presureized side of the VW fuel system is the cause of most engine fires.

Here are some pics of how to fuel filter your VW: https://www.thesamba.com/vw/forum/album_cat.php?cat_id=30
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Wildthings
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Joined: March 13, 2005
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PostPosted: Wed Jun 27, 2018 5:35 pm    Post subject: Re: Mystery Wire in Engine Bay and Fule Filter Question Reply with quote

I just mounted my filter off of the spare air cleaner bracket on the left side of the engine bay. It is on the suction side of the pump and is well supported. The access is great this way. I don't have a problem with not having a screen over the outlet, VW used the screen on the cheap instead of adding an inline filter. Once you add an easily replaceable filter the screen is superfluous IMO.
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Technut27
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Location: Cleveland
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PostPosted: Wed Jun 27, 2018 10:21 pm    Post subject: Re: Mystery Wire in Engine Bay and Fule Filter Question Reply with quote

I finished up the new fuel lines tonight and picked up 6 gallons of fresh ethanol free gas. With a new battery once fuel was through the system it started with much less effort than it had been.

In the end I did replace the filter under the tank to get the crud before it gets into the hardline. It was more of an annoyance than anything. I let the old filters sit over night and when I tapped them on the workbench they were definitely filtering out some junk from the tank. The poor car isn't seeing a lot of action this summer so a real tank cleaning will wait.

Would there be another set of diagnostic wires near the battery? When I pulled the old one there were a handful wrapped up with push on ends taped off. It looked like the bundle went into the engine compartment but I haven't traced them yet.

Thanks for all the tips and finally the fuel gauge works with a new sending unit Smile
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