Wiring an aftermarket cruise control - PeachParts Mercedes-Benz Forum

1985Az300DTurbo · #1 10-23-2006, 09:54 PM

After driving my 85' 300D for 4,000 miles, I've decided I want cruise control that works! Here's my question: How do I provide an rpm input signal for the Audiovox CCS100 Universal Vacuum Cruise Control I purchased? The installation manual says pin #10 (blue) is "Increasing AC Voltage with engine speed". I've resigned myself to installing a magnet on the drive shaft to monitor vehicle speed, but I hoped to use an existing rpm input signal. I would appreciate advice from anyone who's had experience wiring these systems. I found a couple of cool threads on how to wire the factory stalk which I'm planning on doing (thanks a bunch).

Mark

pawoSD · #2 10-23-2006, 10:07 PM

One of the wires in the coupler that connects to the original cruise control box has the speedometer vdo signal on it, this can be used but might not be as reliable as just putting the magnet thing on the shaft. I have the same system sitting in a box right now, I may consider installing it next spring, never got around to it this summer. I was just going to use the magnet pickup kit as well as their provided (and lighted) control pad thing. I was going to leave the original cruise system intact just incase I wanted to use/fix it in the future or something. For now I am not going to deal with it though. My factory cruise works when its warm out, which is when I do most of my long distance driving anyways. I may also try resoldering the brain one more time, I got some improvement the first time so a more in depth attempt at it might work better.

kerry · #3 10-24-2006, 12:33 AM

I installed one of these on my Travco motorhome. I don't have a tach on the Travco so I didn't install any engine rpm info. It's been about 5 yrs since I did it, but I don't see why the cruise needs to know how fast the engine is running. It just needs to know how fast to keep the driveshaft turning. I have found the magnetic pickup to be very effective. I think I wired it on and also added a dab of epoxy.

1985Az300DTurbo · #4 10-24-2006, 10:25 AM

kerry edwards,

thanks for the reply. When I called the 800 technical support line for Audiovox, I was told that the unit needs an rpm signal. It's good to know that you did a successful installation without a rpm signal. In theory, the rpm isn't needed to maintain speed, but I'm guessing it is there for engine safety. For example, if a u-joint coupling between the tranny and drive shaft were to be lost, and the vehicle was cruising along, the vehicle would slow down, the cruise would call for more throttle and which could overspeed the engine. Did you simply ground the rpm input pin? Most electrical circuits don't like "floating input".

thorsen · #5 10-24-2006, 12:04 PM

I have installed two of these units. If the clutch is pressed or the transmission slipped into neutral while the Cruise is engaged, the system detects the sudden rise in rpm and shuts the systm down to prevent redlining the engine. For manual transmission vehicles, the rpm sensor replaces the axle magnet.

I don't believe that you can bypass the rpm sensor. If it was me, I would try to hook it up to the rpm sensor on the front of the wngine and cross my fingers.

kerry · #6 10-24-2006, 02:47 PM

Maybe I just tapped into the distributor wire but I don't recall doing anything like that (although it was 5 or 6 yrs ago). But how would the cruise know whether it was dealing with a 4 6 or 8 cylinder? If you push the clutch in or the driveshaft breaks, how hard is it to shut off the cruise or hit the brakes???

1985Az300DTurbo · #7 10-24-2006, 03:32 PM

I believe thorsen is correct. Although the chances of loosing the mechanical coupling between the engine and drive shaft is very small, it doesn't take very long to redline an engine! According to the installation manual, the rpm input should be wired to the "negative side of the ignition coil". This, of course, is not possible on a diesel engine. I will try to use the existing rpm sensor on the engine (or try to pick off a "conditioned" signal closer to the instrument cluster). I did a quick check of the electrical schematic in my Haynes manual (which is way too small for my 49 year old eyes) and it wasn't obvious, so I'll keep searching. By the way, does anyone know where I can get a more readable elecrical schematic? Poster size would be ideal!

pawoSD · #8 10-24-2006, 04:59 PM

Does the original factory system even look at rpms? I don't think it does....it just looks at the speedo output from the tailhousing of the tranny. Theoretically this is ok though, as it would detect the speed increase there if something broke, and it would back off throttle in an attempt to keep the rear output of the tranny spinning at the set speed. Interesting.

81Wagon · #9 10-24-2006, 07:56 PM

Search is your friend :-)

http://www.peachparts.com/shopforum/showthread.php?t=91987&page=3

Edit:
http://www.peachparts.com/shopforum/showpost.php?p=831670&postcount=14

Dammit, apparently I didn't explain in that first link how to hook the aftermarket cruise up to the stock sensor, so here's the right one. Anyway, the stock sensor puts out approx. 8,000 pulses per mile, so set your new CC to whatever is closest to that. One of the wires that goes to the stock cruise amp under the dash is the sensor wire (pin #11 on mine... it might have been green. Check an electrical diagram). All you have to do is connect that to your new CC and you're ready to go. No magnets required :-).

1985Az300DTurbo · #10 10-25-2006, 10:34 AM

Thanks 81Wagon for additional info. I did check the earlier thread you referenced, but didn't see anything written on the rpm signal, lots on the speedo input signal. I'll use the existing speedo signal input before installing magnets. My only concern is about the engine rpm input. Is it really required? and if so, what's the best place to get the signal. I can always try grounding the signal to see if the circuit logic still works. Thanks again! I really appreciate all of the insight on this forum.

Mark

coreyc · #11 10-25-2006, 11:01 AM

Does this CCS100 work on our diesel cars? I was under the impression that the vacuum cruise units didn't really work well on our cars! I would love to get a reliable cruise set up on my car, but don't want to waste money on something that won't work any better than the factory set up.

Wes Bender · #12 10-25-2006, 03:50 PM

The CCS100 works quite well on these diesels. In fact, there is plenty of vacuum in the system to run the actuator. You tie into the vacuum system rather than the intake manifold. Earlier MB cruise controls were vacuum operated.

Wes

81Wagon · #13 10-26-2006, 02:39 AM

Quote:

Originally Posted by 1985Az300DTurbo

My only concern is about the engine rpm input. Is it really required?

No. If you hit the clutch (not an issue for you) or shift to neutral while the CC is engaged, the RPM input would let the CC know it needs to shut off. I think you're pretty safe without it unless you plan on actually sleeping while using the CC

.