We was called out to a Mercedes A Class which had a very unusual fault, the rear right indicator and front left indicator was simply not working. We checked the usual connections at the front and rear lights and manually powered each bulb to confirm the wiring to each cluster was OK / working. We then looked at live data to confirm if we can trigger each indicator on its own and we still had the same issue. We looked into the module location which controls the indicators, this was located under the passanger floor carpet.
When removing the passanger seat and lower carpet it became instantly known of a bad water ingress / leak issue. The carpet and foam was soaked, Once the carpet was finally removed I found the SAM module which controls the indicators and many more electrical items.It had signs of water ingress, as such we advised the correct repair / fix for this car is to find the source of the leak then replace the SAM unit. Due to the customer wanting it done in a cost effective manner we made a relayed controlled wiring circuit to power the indicators which wasn’t working.
This is a repair thats not garanteed due to the amount of water ingress, but it keeps the vehicle on the road and keeps it road legal. Due to how involved Mercedes electrics are we simply wouldn’t have been able to fix this without a good wiring diagram. If you looking for professional vehicle diagnosis call 07340 341790.