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  #1  
Old 11-04-2003, 07:36 PM
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Wheel Sensor Output for Rally Computer

Sorry for the cross-posting, but I'm not getting any response to this on the Performance Paddock forum. Please see my original posting below:

Howdy, folks. I'm trying to install a rally computer in my 1997 C36 AMG and am hoping someone can help me. Essentially, the rally computer is a hyper-accurate odometer that uses a pulse from a distance sensor to tell you precisely how far you've gone and what your average speed was over some selected elapsed time and/or distance. Typically, the distance sensor consists of a Hall-effect sensor mounted near a rotating part of the drivetrain on which rare-earth magnets are mounted. Whenever a magnet comes by the sensor, it triggers a pulse and lets the computer know that a revolution (or fraction therof) has been completed. Putting the computer into calibration mode then running a known distance, the computer determines a "factor" for how many pulses make up the known distance.

I've installed a computer on our rally car (1984 190E 2.3/5 speed) using this method, but I'd rather not epoxy any magnets to my AMG wheels nor drill any holes in my firewall. I know that the ABS system uses sensors on each wheel, and was hoping to piggyback an input to the computer from somewhere inside the passenger compartment. Suggestions, anyone?
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Rob Fini
Silverphile Bleifuss Motorsports
'07 E350T 4MATIC, 158k miles
'99 E320 4MATIC, 248k miles
'97 C36AMG, 256k miles (gave to son)
'94 E320T, 232k miles
'94 E320T, 251k miles (RIP)
'93 190E Sportline LE, 168k miles (daughter's car)
'92 Coachmen Van Camper, 142k miles
'84 300TDt 336k miles (RIP)
'84 190E-2.3/5spd (Stage Rally Racer)
'66 230 W110 Sedan (Barn Find, Future Vintage Racer)
'64 Plymouth Valiant V200 Convertible
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  #2  
Old 11-04-2003, 07:52 PM
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Rob
If you need a definite answer, let me know, I have electrical diagrams for this car somewhere.

A few ideas, let me know what soounds best to you:

The radio on yours should have speed-dependent volume control, and there is a signal wire into the radio to control that, so this may work, if you can remove the radio (special tool "keys" required to remove the radio).

The speedo receives it's speed signal from the traction control module (I believe yours has traction control, if not, then it would come from the ABS control module). The control module receives all the speed signal, but on this, the signal processed to the speedo and other systems requiring a speed signal is processed off of the left front wheel.

There also may be a speed signal "bus" or terminal in the car someplace you could tap in to.


Gilly
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  #3  
Old 11-05-2003, 12:12 AM
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Thanks for the reply, Gilly. I very much need a definite answer, so I appreciate your offer to verify the electrical diagrams. My car does in fact have ASR traction control and ABS and ETS and VWH (that stands for Very Warm Heinie due to the seat heaters). Since I don't know what processing any of these other modules may perform on the signal and my primary goal is accuracy, my preference is to take the pulse feed directly from the left front wheel sensor. If you don't mind, I'd love to know on which connector the signal is present and where inside the cabin that connector is located. Thanks in advance for your help.

Best Regards,
Rob
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Rob Fini
Silverphile Bleifuss Motorsports
'07 E350T 4MATIC, 158k miles
'99 E320 4MATIC, 248k miles
'97 C36AMG, 256k miles (gave to son)
'94 E320T, 232k miles
'94 E320T, 251k miles (RIP)
'93 190E Sportline LE, 168k miles (daughter's car)
'92 Coachmen Van Camper, 142k miles
'84 300TDt 336k miles (RIP)
'84 190E-2.3/5spd (Stage Rally Racer)
'66 230 W110 Sedan (Barn Find, Future Vintage Racer)
'64 Plymouth Valiant V200 Convertible
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  #4  
Old 11-05-2003, 06:29 AM
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OK Rob. If no one else is forthcoming with the info today, I'll look at my diagrams late this afternoon/this evening.

Gilly
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  #5  
Old 11-05-2003, 06:40 PM
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Ok Rob, got it all figured out for you. One forwarning though is that this IS the VSS signal, but it's an A/C signal, not an on/off (digital) signal.

Located in the right side of the floorboard there is an area with several connectors. To get to it you'll probably have to remove the right trim on the floor inside the passengers door opening, then push back the carpetting a little, not that bad to do. Under the carpetting on the extreme right there will be a bib black plastic conduit, which should unsnap pretty readily, and you'll see lots and lots of wiring in there. The one you need is called X47. The description of X47 is "Rear axle RPM sensor harness connector (6 pole). OK, I'll try to describe which one it is. The very front connection in the group of about 10 connectors is a very large gauge RED wire terminal (a terminal being some wires with "eye" connectors on the end, all secured together using an insulated stud and nut). OK, so that real big red wire we'll say is #1 (it's the feed to the fusebox and other large consumers in the front of the car, like the starter). There may be a series of studs behind the big red #1, or there may be no more of this type of connector. In the earlier cars there were some VSS connectors there, but the 97 they changed quite a bit, and not sure if there will still be terminals there that WOULD have been used, or if they got rid of them all together. I'm pretty sure there will be one small terminal just behind the one big red #1, and after that there will either be NO more stud-type terminals, or maybe 2 unused ones. After that, you will find a couple more typical electrical connectors (push-together type connections). X47 will probably be the second of this type of connectors. It should have spaces for 6 connections. I can give you some idea how to make sure you have the correct connector by telling you the wire colors:
"Oh shoot" (thinking out loud here), they show an X47 connector 1 and connector 2. Hopefully you can get in there an find out what's up. The one you need is called connector 2, and they say it's terminal #2 on that connector. The wires you need are Green with a Black stripe. On one side of the connector there is one of these wires (from the ETS/SPS control unit) and the other side there are 2 wires (all black with green stripe). The 2 wires-one goes to the radio (auto volume control) and the other goes to the PSE control unit under the back seat (unsure why it needs this info, possibly the doors auto-lock at a certain speed?)
On the X47 connector one, (should be near the connector 2 that you need), terminal 1 is black with yellow strip (both sides of the connector, term 2 is black (both sides), term 3 is white with a yellow stripe (both sides), and term 4 is a white wire (both sides).
There is no dedicated wire to the instrument cluster like I thought, the speed info I now believe on a 97 is fed to the instrument cluster through what is called a CAN data bus (serialized information line).
Also it looks like that green/black wire data is actually fed from the RIGHT front wheel, not the left, just so you know. The info is coming from the ESP/SPS control unit.
If it's easier for you, you can also find the other side of the green/balck wire behind the radio, it may be easier for wiring the unit. On the radio back, it's connector A, pin 1 (again, green wire, black stripe, should be easy to identify.

Gilly
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  #6  
Old 11-05-2003, 10:23 PM
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Wow! Thanks, Gilly. That's some bit of information that I need to digest. This might be a case of a picture being worth a thousand words - is there some way I can get my hands on a copy of the wiring diagrams for my car? Thanks again for the information and I'll be sure to let you know how I make out.
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Rob Fini
Silverphile Bleifuss Motorsports
'07 E350T 4MATIC, 158k miles
'99 E320 4MATIC, 248k miles
'97 C36AMG, 256k miles (gave to son)
'94 E320T, 232k miles
'94 E320T, 251k miles (RIP)
'93 190E Sportline LE, 168k miles (daughter's car)
'92 Coachmen Van Camper, 142k miles
'84 300TDt 336k miles (RIP)
'84 190E-2.3/5spd (Stage Rally Racer)
'66 230 W110 Sedan (Barn Find, Future Vintage Racer)
'64 Plymouth Valiant V200 Convertible
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  #7  
Old 11-05-2003, 10:32 PM
Gilly's Avatar
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Rob
Depending on where you want to mount this thing, probably all you really need to know is the last paragraph; probably going to be easiest to just splice into the signal going in to the radio.

Gilly
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  #8  
Old 11-05-2003, 11:23 PM
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Location: Millville, NJ
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Can you give me any details on the signal itself, like voltage levels or correlation to speed? Also, does the signal come from the rear axle or the right front wheel (your message said the one connector is for the rear axle RPM sensor harness connector, but also said another one comes from the right front)? I'd prefer the front, as I do sometimes spin the rear wheels (believe it or not), which would result in an inaccurate measurement.

Also, what's your take on whether or not tapping into the harness would void my Starmark warranty? My car is scheduled for a bunch of seal replacements next week and I'll probably ask the guys at the dealership about this while I'm there.
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Rob Fini
Silverphile Bleifuss Motorsports
'07 E350T 4MATIC, 158k miles
'99 E320 4MATIC, 248k miles
'97 C36AMG, 256k miles (gave to son)
'94 E320T, 232k miles
'94 E320T, 251k miles (RIP)
'93 190E Sportline LE, 168k miles (daughter's car)
'92 Coachmen Van Camper, 142k miles
'84 300TDt 336k miles (RIP)
'84 190E-2.3/5spd (Stage Rally Racer)
'66 230 W110 Sedan (Barn Find, Future Vintage Racer)
'64 Plymouth Valiant V200 Convertible
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  #9  
Old 11-05-2003, 11:42 PM
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Join Date: Mar 2001
Location: Evansville WI
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I don't think it would mess with your warranty any more than say installing an aftermarket cell phone, or hardwiring a radar detector. I wouldn't worry about it.

I can't describe the signal any more than I have (it's an AC signal, varies with speed). Should work, can't say for sure. I'd assume the other type of signal (with the driveshaft or independent wheel speed signal) would also be an AC signal.

The signal, as I mentioned, comes from the right front. MB put this wire connection (for the radio and PSE) into the rear VSS connector, no better place for it I guess. The ESP control unit is processing all the wheel speed signals, but the diagram says the Right Front is the one being passed to the interior.

If you don't have the tools (special tool keys) to remove the radio head unit, maybe when you bring it in you can ask him if he'll just get the head unit part way pulled out so you can access the wiring.

Why would you need to know the signals corelation with speed? Doesn't the calibration mode take this into account?

In regards to getting wiring diagrams for your car, you mean PLURAL as in all of them, or just for the VSS or what?

Gilly
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  #10  
Old 11-06-2003, 07:22 PM
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Location: Millville, NJ
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I need to know the correlation to speed so that the rally computer's internal counter doesn't overflow from too many pulses. An adapter that turns the AC wave into a square wave is a piece of cake, but it gets more complicated if I need to make it a divider, too. I suppose it would be nice to know what peak-to-peak voltage levels to expect, but with a 12V system it can't get too outrageous. If worse comes to worst, I suppose I could hook up an oscilloscope to it and just measure the damn thing.

All of the wiring diagrams would be great to have, as would a real factory service manual like I have for my 123 and 201 chassis. Any tips on where an owner can procure them?

By the way, I really appreciate the time you've taken to look this stuff up for me and to relay the information to me here.

Very Best Regards,
Rob
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Rob Fini
Silverphile Bleifuss Motorsports
'07 E350T 4MATIC, 158k miles
'99 E320 4MATIC, 248k miles
'97 C36AMG, 256k miles (gave to son)
'94 E320T, 232k miles
'94 E320T, 251k miles (RIP)
'93 190E Sportline LE, 168k miles (daughter's car)
'92 Coachmen Van Camper, 142k miles
'84 300TDt 336k miles (RIP)
'84 190E-2.3/5spd (Stage Rally Racer)
'66 230 W110 Sedan (Barn Find, Future Vintage Racer)
'64 Plymouth Valiant V200 Convertible
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  #11  
Old 11-06-2003, 07:40 PM
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Quote:
Any tips on where an owner can procure them?
Yeah, my basement.

Gilly

ps Stay out of my basement
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  #12  
Old 11-06-2003, 07:43 PM
Gilly's Avatar
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Location: Evansville WI
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Or call the 800 number for mercedes, and there will be an option on the recording for talking to someone about something like "documents and technical publications". Get someone on the horn there at MB and tell them you want to order the ETM's (wiring diagrams) for the 202 chassis. It's 2 volumes, I'm guessing $100/ea.

Gilly
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