The importance of electrical grounds (was: wipers quit sitting 8 months)

[Cees Klumper]

We returned to France for the Summer last Monday and all was well with the Pagoda, save for one thing: the wipers no longer worked. Sitting under cover in a barn in France for 8 months can introduce issues like that.
After checking the fuses and verifying that the relay clicks when pressing the 'on/off' switch, I turned my attention to the motor itself. First pulled off the 4-prong connector and cleaned the contacts thinking it might be due to corrosion from humidity, but that wasn't it either. Then checked whether power was making it to the plug itself: it was. However, I noticed the voltage dropped considerably when I moved the wiring loom back and forth. It turned out that the motor gets its ground from a wire that comes out of the loom close to the motor, that is attached to the inside fender with a small screw. That screw was loose, and apparently some corrosion had formed underneath, enough to compromise the ground. Cleaned the contact surface, tightened the screw and voila, wipers back on track.
Always satisfying when I'm able to diagnose and fix small-ish issues like that.

[lpeterssen]

Dear Cees

Congrats for your Sherlock Holmes discovery.  Grounds are always forgotten.  Modern Mercedes and BMW  have evolved significantly on the quality of the grounding post. Those are special surfaces highly polished where the terminals are tighten with 10mm screws and are always raised from the rest of the body structure.

I think that time has teached the designers that grounds are always overlooked and cause many erratic problems on the different components of an electrical system.

I would recommend to all you that pay attention to your electrical stuff, to polish each of your grounding post on your loved MB classic.  On the pagoda there are not many, but as far as I remember:

1. Main ground post on the cabin behind the heater controls, accessible if you remove central instrumentation and steering wheel

2. Ground post on each side of your radiator, on the lower part. These ones are responsible of headlights.

3. Ground post on the right fender, as mentioned by CEES, responsible of the wiper motor

4. And the. MOST important the GROUND STRAP between transmission housing and the firewall. This ground allows the starter to work at its maximal speed and also brings ground to many electric selenoid or valves installed on the engine to run the cold start system, among other functions.

5. Also in some cases there is a ground post next to the left fender relays arrangement that allows those components to work properly.

Always sand the ground surfaces. Start with a coarse grit like P80, and finish polishing the area with sand paper grade P180.

APPLY CONDUCTIVE GREASE, no matter if it looks terrible or tarnishes your hands, it is imperative to use CARBON CONDUCTIVE GREASE for those ground terminals.  Only with that you can assure that corrosion will not build up between cable terminal and the grounding surface.

Of course the BATTERY NEGATIVE main cable ground to Chasis should be in acúlate clean.

Here a link of the conductive grease I use in my projects:

MG Chemicals - 8481-1 Premium Carbon Conductive Grease, 3 fl. oz, Black https://a.co/d/bsFErco

Sold in Amazon.

MG Chemicals - 8481-1 Premium Carbon Conductive Grease, 3 fl. oz, Black https://a.co/d/5CExfPj

Best regards
L.Peterssen

[BobH]

Thank you Leo, your valuable advice is always gratefully received

[jerryef2@aol.com]

Ignition on and off turns on wipers but wiper switch doesn’t turn on or off.  Wiper switch does control speed.

[rwmastel]

Jerry,

Is this a question about your car?  Are you trying to convey how things operate normally?  What model Pagoda do you have?

Also, welcome to the Group!  I see you're in Ohio, there are several owners/members in Ohio.  Meeting other members and their cars is the best way to learn things.  Also, we're having a huge event in Chicago soon - probably 90+ members and 40+ Pagodas.  It might benefit you to attend that.  It happens only so often!

[Pawel66]

If I may, with regard to ground posts catalogue: there is also a ground next to the tail lamp that may give or have given some of us major headaches…

[lpeterssen]

Excellent that the topic name was changed to IMPORTANCE OF GROUNDS.

It Is now more descriptive.

And also thanks to my friend Pawel for his additions to the subject.

Best regards
Eng. Leonardo Peterssen