Relays and fuses

[Suki]

Hi,
Firstly I would like to thank all participants of the forum. It is extremely valuable and is the first place I look to when I have an 'issue' with my 124 or 202!

I had a problem that I would like to share with people.

Car: 124, 230e K reg saloon.

Last night the following things stopped working:
Wipers
windows
rear de mister
main beam, when I pull the indicator stalk towards the steering wheel (I could however get the main beam on when I pushed the indicator stalk away from the steering wheel!)

The rest of the car was ok. My first port if call was to check all the fuses. I performed a visual inspection and they all seemed fine. After reading the forum I suspected that the fault was the combination relay. I tried opening the relay and spraying wd40 into the mechanism, but this did not work!

Today I started from scratch and decided change the fuse as a basic prelim check. To my surprise I noticed that the fuse had a nice solid black ring of carbon where the fuse holder touches the fuse! It seems that over time there must have been a carbon build up which got worse over time! I managed to sand the carbon off with a piece of wet and try and hey presto.. all fixed!


Lessons learnt.
Always check the obvious
change the fuse as a matter of course!
don't think that just because the main beam comes on when pulling the stalk to you and away from you uses the same fuse!!!

 

[television]

On some other threads I have told people to check for marks on the fuses.
The marks are caused by arcing, and to clean and turn them around.

PLEASE DO NOT USE WD40 ON LOW VOLTAGE ELECTRICS and that includes control boxes, there are plenty of switch cleaner's on the market that come in small pen tubes with a pull out tube applicator. Do not use aerosol cleaners on switchbanks and control boxes for the same reason that airlines are not used for cleaning engine components anymore. they just force dirt into the corners and it comes back at a later date.

Electrics in our car's sinse 1990 contain very sensitive components, that includes CAN buses,Eproms, CMos and Opto electrics. Some ECU boxes have automatic sockets that short circuit all of the pins when they are removed to prevent static short circuits and flashovers. They are in fact so sensitive we have to wear earthed wrist bands while working on them and the workshop has to be static free. Circuit boards contaminated with the wrong cleaners have to be sent away and washed in ultrasonic cleaners.

Many people do not know that MB have a complete range fusebox and wiring update kits, these include part wiring harnesses for all models.

 

[c13tay]

The multifunction relay is usually the fault - if you take it apart it will be obvious which soldered joints have broken (it was on mine) re-soldered and now working fine