Cruise Control Question

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

[stevebfl]

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.



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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

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!

[Benzmac]

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.

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Benzmac:
Donnie Drummonds
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM