Today I sat down and figured out how to wire the stock control stalk to my aftermarket cruise control (a Rostra GlobalCruise electric cruise control). From my research it seems that most (if not all) aftermarket cruises nowadays use the same two control stalk wiring setups; one that is open-circuit (or "normally open") and one that is closed-circuit ("normally closed"). Both types are supported by the Rostra unit, and I think this will be the case for most other aftermarket cruises as well. wolf_walker wired his stock controls up as closed-circuit controls, which have a complex and ugly setup and required him to use a relay and a diode to get it working. If it's possible, wiring the stock controls up as open-circuit ones instead is a simple 5 minute job requiring no extra parts . The stock controls in the 123 has a 5 pin connector. Here's what each is for, and the color of the wire associated with it: 1: Gray wire, always +12 except when controls are in "off" position 2: Red/yellow wire, +12 power 3: Yellow/green wire, +12 when controls are in "decel" position, neutral otherwise 4: Green/red wire, +12 when controls are in "accel" position, neutral otherwise 5: Blue/red wire, +12 when controls are in "resume" position, neutral otherwise The open-circuit aftermarket cruise control setup wants this (wire colors should be standard but no guarantees!): Brown wire: always +12 except when controls are in "off" position Red wire: +12 power Yellow wire: +12 when controls are in "resume/accel" position, neutral otherwise Green wire: +12 when controls are in "set/coast" position, neutral otherwise Wiring for power is obvious (red/yellow wire on stock controls to red wire on aftermarket cruise). Wiring for the off switch is also obvious (gray wire on stock controls to brown wire on aftermarket cruise). After that, wiring is somewhat a matter of personal preference. The stock controls have 3 switches besides "off": accel/set, decel/set, and resume. None of these coincides perfectly with the 2 the aftermarket cruise wants: resume/accel and set/coast. Take your pick of two the remaining three positions and connect the appropriate wires, or jumper two of the stock wires together so that two of the positions perform the same function. My personal preference: On the stock controls, "accel/set" is now "resume/accel" because it makes sense to me to push up to accelerate, and tapping up once for resume will be easy to remember. (Green/red wire on stock controls to yellow wire on aftermarket cruise). On the stock controls, both "resume" and "decel/set" are now "set/coast". This way decel/set still functions as would be expected, but I can also turn on/set the cruise control by pulling towards myself rather than pushing down (pushing "decel" to set the cruise control seems counterintuitive to me). (Both Blue/red and yellow/green wires on stock controls to green wire on aftermarket cruise). Good luck to everyone else trying this mod! It's totally worth it - a functional, smoothly-operating cruise control *with a 3 year warranty* for much less than the cost of buying a new cruise amp that will probably crap out a year later...

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'81 300TD Wagon 355k (Miss Diesel)
'83 300SD 180k
'84 500SEL 190k (Parting it out)

hmm... just to clarify your meaning are you saying "buy an after market "open circuit" type Cruise controll so the modifications to the OEM MB wiring will be easier."? If this is correct how might one recognize that the after market CC is open or closed wired?

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"If anyone knows other lessons I need to learn, please tell me. I'm tired of learning them the hard way".
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The Glow Plug Wait: This waiting period is a moment of silence to pay honor to Rudolph Diesel. The longer you own your diesel the more honor you will give him". by SD Blue

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62 UNIMOG Camper w/617 Turbo, 85 300SD daily driver- both powered by blended UCO fuels

Yes, the wiring would be much easier if you got the open-circuit type. I think most likely both types of controls would be supported by whatever aftermarket cruise you buy (it's just a matter of setting the right dip switch to tell the unit which type you're using). If it doesn't say in the published specs of the unit you're buying (Rostra specifically mentions they support both control types), you should be able to download the owner's manual from the manufacturer's web site before you buy and it should tell you.

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'81 300TD Wagon 355k (Miss Diesel)
'83 300SD 180k
'84 500SEL 190k (Parting it out)

Yep, the docs I looked at for the Rosta setup showed it would work both ways. My relativly anciant vac servo systems have only the one option, hence my slightly complicated setup.

On mine pull back and up resume/accel, down is decel/set. I don't even think about it anymore.

Great, serious thanks from the depths of my heart for putting this in an intelegable fashion. I just have not been able to get it to make sense in text and am so insanely out of time for anything anymore. Now everyone can have a good cheap long lasting cruise with a clean instal.

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1982 VW Caddy diesel 402K 1.9L AAZ
1994 E320 175K

81 Wagon,
Can you please provide the exact Rostra model and part number you used? This is exactly the mod I wish to do. Factory appearing modern CC install/upgrade.... Can't wait! Thanks, RT

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93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

Check out this Rostra site. I followed the "local distributor" links to find the unit at a nearby Pep Boys.
http://www.rostra.com/cruise-control.htm

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Rick
Avid Benz watcher

Previously owned 126's: 2 1981 300SD's, 1987 300SDL, 1991 350SDL,
Previously owned 123's: 1978 300D, 1983 240D, 1985 300D
Previously owned 124: 1994 320TE

Current Asians:
'00 Toyota Avalon, Silver, gray leather, 287k
'02 Toyota Avalon, Gold, tan leather, 123k
'03 Chevy Suburban, Z71, tan leather, 190k

Um, no distributors in RI or MA, some in CT.... Looking for the Rostra part number mainly. I contacted a manufacturer a while back and was told the CC wouldn't work with the MB control stalk. Don't remember if it was Rostra or not, just want to be sure.

Edit: Evidently Rostra makes CC units for Audiovox, I found that PepBoys in RI supposedly carries them.....

RT

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When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

I bought the electric (not vacuum) model described on the page rgp123 linked. They do seem to make the units Audiovox sells (at least they sure look identical!) and those might actually be cheaper and easier to find (I bought my Rostra-branded one online).

When they say it won't work with the MB control stalk, they mean it isn't a simple plug-and-play affair... Which is why the rewiring I described above is necessary (the manufacturer definitely wouldn't support this, but it works fine :-).

I'll take a picture of my setup under the hood in a few weeks if you want (my digital camera is currently touring Italy without me). If you need it sooner I could probably borrow a friend's camera...

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'81 300TD Wagon 355k (Miss Diesel)
'83 300SD 180k
'84 500SEL 190k (Parting it out)

I thought that stock amps were overloaded when the stock actuators were drawing too much current from the amp's output section. If you're going through stock cruise amps the culprit is likely the actuator. Why not keep it stock then? Just fix your actuator.

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'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)

This system is all new with the exception of utilizing the stock control stalk as explained in the above post for rewiring. The Rostra system is electronic with a new actuator and amp. It will be much more reliable than OE but with the look of stock by using the OE control.

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Rick
Avid Benz watcher

Previously owned 126's: 2 1981 300SD's, 1987 300SDL, 1991 350SDL,
Previously owned 123's: 1978 300D, 1983 240D, 1985 300D
Previously owned 124: 1994 320TE

Current Asians:
'00 Toyota Avalon, Silver, gray leather, 287k
'02 Toyota Avalon, Gold, tan leather, 123k
'03 Chevy Suburban, Z71, tan leather, 190k

If one's speedo in his 123 is jumpy, does that affect his CC? Is the CC dependent on the speedo? Mine works and then it doesn't, just like everyone else's. But when it works it seems smooth and stable despite the jumpy speedo. I'd like to have a fully functioning CC, but just focusing on the CC itself ain't gonna cut it if it's speedo-dependent cuz my speedo's f'ud up.

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'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)

The Rostra unit referenced in this thread has several methods of pick up. The simplest is with electronic speedo input but magnets attached to opposite sides of the driveshaft is pretty easy as well and works without input from your speedometer.

__________________
Rick
Avid Benz watcher

Previously owned 126's: 2 1981 300SD's, 1987 300SDL, 1991 350SDL,
Previously owned 123's: 1978 300D, 1983 240D, 1985 300D
Previously owned 124: 1994 320TE

Current Asians:
'00 Toyota Avalon, Silver, gray leather, 287k
'02 Toyota Avalon, Gold, tan leather, 123k
'03 Chevy Suburban, Z71, tan leather, 190k

For about the same price and installation effort you could probably just replace your speedo cable rather than installing the magnetic sensors on the driveshaft.

__________________
'81 300TD Wagon 355k (Miss Diesel)
'83 300SD 180k
'84 500SEL 190k (Parting it out)

I'm not sure about this particular unit (haven't read the included list) but most include the magnets, pick up and wiring harness in the kit. All you do is cut a string to the length of the driveshaft circumfrance, then cut that in half to use as a measure for mounting a magnet on either side of the shaft, exactly opposite each other. Drill to mount the pick up nearby then thread the wire through an existing firewall hole.

That seems much simpler, and cheaper, than replacing a speedo cable. However, if your speedometer is a problem anyway, a repair there will probably be cheaper than a speeding ticket!

__________________
Rick
Avid Benz watcher

Previously owned 126's: 2 1981 300SD's, 1987 300SDL, 1991 350SDL,
Previously owned 123's: 1978 300D, 1983 240D, 1985 300D
Previously owned 124: 1994 320TE

Current Asians:
'00 Toyota Avalon, Silver, gray leather, 287k
'02 Toyota Avalon, Gold, tan leather, 123k
'03 Chevy Suburban, Z71, tan leather, 190k

The rostra unit is about $30 cheaper without the magnets and pickup (at least where I bought it from). Fastlane lists the speedo cable for $35. It seems worth the extra effort to have a functional speedometer :-).

__________________
'81 300TD Wagon 355k (Miss Diesel)
'83 300SD 180k
'84 500SEL 190k (Parting it out)