Have you had issues with mysterious power interruption or gremlins, maybe with wipers, headlamps, radio, indicators and various other sections of the vehicles electrics? – well the common issue is the fuse box distribution module that lives beneath the steering column on a T1N Mercedes Sprinter.
This highly complex ‘box of tricks’ contains a matrix of brass interconnections, distributing power to many circuits through fuses and plug connections. It also contains the integrated flasher control circuitry electronics for the indicators and intermittent wipers. What usually happens is the board suffers corrosion, usually caused by a spilled drink or liquid that makes its way inside the steering column and starts the electrolytic corrosion process off. Sugary drinks such as coke or a sweet tea or coffee will do nicely. Of course on occasion its just damp and condensation that sets the whole bad connection scenario off, but for whatever reason this is the centre of all electrical connection to the vehicle and more often than not is the source of a catalogue of seemingly untraceable electrical faults.
It is quite simple to remove and service / clean up although the Mercedes people would prefer to sell you another one at a princely sum.
First start by removing the under wheel door flap that covers the fuses on the distribution panel. Then remove the cowling that forms the lower part of the steering wheel column cover. Two cross head screws at the top and a single 10mm nut at the base will remove the plastic cowling. Once removed undo the single 10mm fixings top and bottom, then flip up the protective disc and remove the large red power lead eyelet. Make sure you tape this up as it remains at permanent +12 battery potential regardless of ignition position.
Once the fixings are removed and the large wire is protected pull out the top of the board directly from the two connectors beneath the steering wheel. Once this is out the board will pull down to allow you to remove the connectors behind. Once all these are removed the unit can be lifted away from the column and inspected.
You can see from the pictures where the problem lay with this unit, several of the brass spade connectors had started to corrode, there were easily cleaned up once the unit was split open. This is done by simply removing the three small relays and the bottom edge moulding first, then further undoing the 10mm brass nut and washer that holds the unit together on the main power pin. (the same stud where the thick red cable connects) Once this is removed the unit will allow the black plastic cover side to be removed. This will facilitate the easy cleaning and inspection of the tags that connect with the molex loom connectors.
You can see the level of corrosion on the terminals, that once cleaned, (Don’t forget the plug spades as well!) will allow good electrical connection to made between the two mating parts. Once clean the unit can be reassembled and fitted back in pretty much the same way as it was removed. Sometimes due to a weak moulding, the threaded insert in the column plastic fails, preventing the secure fastening of the fuse board at its top edge. The best cure for this is to remove the insert with careful use of a screwdriver and prize it out, then using a strong tie-wrap as pictured to secure the whole assembly.
You may find that some of the fuse carriers have also corroded on the visible side of the board, the unit can be further dismantled to reveal the internal components of the holders that can be cleaned in the same way as the rear connectors. However the most common cause of problems will be in the multi-way connectors on the rear of the unit. Do not forget to clean the relay tabs that lie beneath the unit before re-inserting the relays into position. Test the electrics before fitting the cowling and you should be good to go !