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Old 04-02-2000, 10:47 AM
Posts: n/a
Greetings all,
After reading all the prior posts on the subject (56) I am now ready to attempt repair on my cruise control, I just purchased a 85 190E 2.3 last Friday, the C/C does not work at all, my question is: The PO had installed a "3rd" brake light he tied into the wiring in the trunk below the latch. Before I track down the problem with C/C should I disconnect the "3rd" brake light unit or just make sure proper bulbs are installed? Will the extra wiring and bulb create a difference in the resistance causing an effect on my soon to be repaired C/C? Or will it have nothing to do with it because the C/C uses the tail light not brake light circuit? I put in a request for price for the C/C Amp. with the Parts Shop as I understand this is the most common failure.
Thanks for running this board! I just love it! Thanks for the input! Mutt
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Old 04-02-2000, 12:31 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
The cruise control does use the brake light circuit for a digital command. The ground through the bulbs is a zero and anything else is a one. If you have a one (high) then cruise is disconnected. Thus burnt bulbs cancel the cruise. Having extra bulbs is of no consequence .

Although the control unit is often the problem, a proper diagnosis should be done. We use MBs tester which plugs into the harness where the control unit would. It verifies: power, ground, all switch positions, brake light circuit, speed signal (turns a light on at 35kph) and most important it has a button that when pressed, with the ignition on engine off, the actuator goes full sweep.

With a wiring diagram all the above tests could be simulated, including the actuator. The actuator is close to a tie for most common problem.

BTW when you ask about the control unit check out rebuilts. This is a high dollar item and rebuilts are available for near half price.

Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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Old 04-02-2000, 04:36 PM
Posts: n/a
Thank you once again Steve for sharing your knowledge and expert advice! I put in a request for all the prices (new and rblt). I will ask around and try to find out who in my area has one of those testers. Happy Motoring!
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Old 04-02-2000, 09:41 PM
Registered User
Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
Mutt, we sell the wiring diagrams in the Service CD for the 201...A good buy if you are going to work on it yourself.

Donnie Drummonds
1981 280GE SWB
1987 16V
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