Failure of electrical components within the doors due to defective Wiring.

This information has been received from Teemu Keso Who suffered electrical failure of the Mirror windows auto locking etc due the falty wiring within the rubber Boot located between the A post and Front edge of the door

W169 drivers door intermittently having no power. Effecting sporadically power windows, central locking, mirror adjustment and turn signal at mirror. Dealer, and all other workshops suggested that problem must be at the door control unit.

Actually fault is the broken earth lead inside rubber boot, between the driver's door and the car body.

I attach a picture of my findings, see below


1. Disconnect the battery, ( Ensure you follow the correct This is important as there are air bags in at least the front doors of the A class which could be accidental operated while working on the loom to locate the fault

2. Remove the Door card ( Careful removal will allow the securing clips to be re-used

3. Unplug two connectors from door control unit.

4. Carefully remove the corner plastic cover located on the in the foot well on the effected side.

5. Gently ease the cables for closer inspection. (It is good advise to attach a pull cord to the cable at the door end to allow retrieval should they be pulled from sight after examination of the loom and repair

6. Examine the Cables for damage of break ( it is worth noting the that the in some cases the external outer casing can be intact but the conductor wore broken in such cases a volt meter would be useful)

7.Replace the damaged cable with suitable Automotive Loom cable.

(Where all services have failed the live or Earth cables are suspect.)

8 To avoid further problems ensure any repair is well insulated and secured If possible a solder joint would be preferable.

9 Where the affected cable is replaced at length ensure the new cable is secured to the individual damaged cable which can then be used to pull the new cable through the boot to the inside of the door.

10.In this case only one cable, the earth was at fault and replaced 20cm (10"inches of cable was replaced.

11 And put it all back in reverse order (If the outer loom cover has been opened to access wiring close and protect using suitable protective tape)

12.Reconnect the battery and test all services for correct operation


















1. Door card.....2. Plastic panel to be removed to access cables /loom..... 3 defective cable located.....4 Rubber boot in which defective cable in located.







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