My guess is for an amplifier. That cable probably goes all the way to the trunk.

Old pre-filter--looks pretty grimy in there



New spin-on:

You shouldn't need the primer pump for a filter change. Try cranking it and that old gal should push through the bubbles. Also, do you use an additive in your fuel? I always run Diesel 911 (there are many brands and I'm sure someone here will ring in on their favorite to give you some other ideas). If the filters are a gunky issue, then the lines will have some build up, the tank will be cruddy, etc. A diesel additive will help clean the system and remove any moisture.

On the vacuum, you mention earlier in this post that you want to tackle that system and get it to the bare minimum to see if it changes the shifting. With that one nipple capped off, that is the bare minimum I'm afraid. The first place to start is to replace that line from the pump to the booster. That's about $30, and very well worth it. Also, the rubber connectors look cracked. Those little b**tards can drive you nuts of one of them is leaking. That's an annoying and surprisingly expensive job (I think that was about $30ish, too, but for dang little rubber bits, just felt like a lot!) but also a very good idea. I learned to do that with the first one of these I bought and have saved myself headaches by doing it on all of them right off the bat after.

Another thing to look at is the ALDA system. Here's a great walkthrough on cleaning a banjo bolt and line that gets gunked up over time. We did this on our rust...I mean...wagon and BOY what a difference that made on shifting and just general happiness of the vehicle.

Mercedes ALDA boost system service

Good luck!

__________________
Current:
1980 300D "Blush"
1985 300TDT "Walter"
1995 e320 wagon "Sopwith Llama"

Greatly missed:
1985 300TD "R2D2"

Don't really miss much at all:
1983 240D "Dee"

are you in Galveston?

__________________
1986 560 SEL
1960 Ranchero
1970 Cougar XR7
2002 Crown Vic Sport
1992 F150

New York City

Is it really safe to crank the air out of the filter without priming beforehand? I don't want to end up with air further down my fuel system. As of right now, the filter is only about half full (see attached photo)

Attached Thumbnails

 

Did you replace both filters? Or just the small one? I know you posted a picture of the large spin on filter but I didn't quite catch if you had actually installed it yet.

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1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

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Left to Right - UberWasser, Iridium, Stuttgart-->Seattle,, mannys9130

Visit the W123 page on iFixit for over 70 helpful DIY guides!

Haven't installed it yet. Waiting on the o-rings and Diesel Purge to get in before swapping the spin-on out. The old one Should still be full of fuel.

Then it's fine to just crank to start. There's very little air in the pre-filter. Also, you will find that it is never really full of fuel, there is always a small pocket of air in there.

The large spin on filter is another story. You should fill that up with fuel, fresh motor oil, veggie oil, diesel purge etc (combustible fuel of some kind basically) right to the brim before installing it. And then pump it up with the primer as well.

__________________
1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

The Baja Arizona Oil Burners Send a message if you'd like to join the fun
Left to Right - UberWasser, Iridium, Stuttgart-->Seattle,, mannys9130

Visit the W123 page on iFixit for over 70 helpful DIY guides!

Great. thanks for the tip. If she starts back up, the inline filter will have been the primary problem. If not, then onto bigger challenges.

She's back from the dead! Blew out a huge amount of smoke upon starting (scared the neighbors off their stoop), then idled rough for a little. Shut her off, started her back up and no smoke on the second round. Still not as smooth as before, but I've only let her idle for a couple of minutes.

Good to know that it was such a simple problem. I think I'll continue to go ahead with the replacement of the spin-on filter, diesel purge and certain leaking fuel return lines, just for the peace of mind.

Wow, that pic really shows how bad off the main vac line is.. I didn't know both nipples were jacked up.

My advice, considering all the good information posted already, would be to grab some StarTron tank cleaner. It breaks down a lot of the gunge that builds up in the fuel tank. A benefit of that is that the guide wires for the fuel sender will be cleaned somewhat and give your fuel needle a considerably more accurate reading.

Fuel Sender 85 300D- Cleaned (Pics)

Star Tron

__________________
1977 Red 240D ( Squished by a 18 Wheeler )
1976 Black 240D ( Sold )
1991 White 420SEL ( Sold )
1987 Black 560SEL ( Sold )
1983 White 300SD ( Sold )
1984 Blue 300SD ( Sold )
2014 Red Chevy Cruze Diesel ( New Hotness )

Some updates: took her on a ~700 mile round-trip to Burlington and back (which, in hindsight, was pretty ballsy [edit: dumb is more like it], considering my overall uncertainty regarding the condition of the vehicle).

The good news:

• No major fluid leaks
• Proper (~30) MPG for highway driving
• Handled pretty well on the highway. Needs new tires as well as an alignment, but good other than that
• Made it there and back

The bad news

• LEAKS. SOMEWHERE. I'd had some experience driving her in rainy conditions, and things seemed perfectly fine. However, the rain this past weekend was TORRENTIAL, and I discovered a small lake forming in the rear passenger side footwell. The wheel wells and floors are rust-free, so I'm suspecting a rear window seal leak, or a sunroof-related leak.
• Confirmed the presence of gunk in my fuel tank. Made the mistake of parking her nose-down on a sharp incline, and the same rough/no start and power-loss returned. Parked her on the same incline nose-up the next day, and she started and ran like a top.
• Transmission is still a little wonky. Essentially completely unpredictable. Seems to be happiest on long highway stretches, and seems to run smoother cold (??). In city driving, will sometimes behave just fine, but occasionally flares, clunks and shifts hard on a seemingly random basis (generally only once the transmission has warmed up, however). I don't suspect that the transmission is completely gone, since I know that it's capable of shifting perfectly when it feels like it.
• Fuel cap seal seems to work well. When filling up, the car starts to leak diesel fuel out of the tank lines and from another unidentified point under the rear passenger fender. Once the cap goes back on, the leak stops. I'm guessing the pressure created by the seal might be holding the fuel in?
• Rough start after sitting for the evening. For the first start of the day, the engine starts a little rough (as if it was a little short on fuel). Give her some gas, however, and she's fine for the rest of the day.

Looks like it might be a power cable for a stereo amp or maybe some kind of old two way radio