On Friday the 9th of April, I traveled to the North-west of Friesland to pick up an OBC2 for my E28 M5. There has been some debate about whether or not an E28 M5 has the OBC2 fitted as standard, but a fact is that #231 does not have any. Also the wiring loom was not present and has not been messed-up with. The entire wiring of #231 underneath the dashboard is original. As individual OEM parts, the OBC2 is hideously expensive, but from time to time, complete sets are offered on the bay of e for reasonable money. I did not source my set on the bay of e, but directly from fellow E28 enthusiast Ivo who has a nice parts-bin of E28 parts lying around.
The OBC2 set consists of (see picture below):
The OBC2 unit with the coding plug.
The outside temperature sensor.
A relay box for the alarm horn (PIN code protection)
Primary wiring loom.
Secondary wiring loom for relay box and option-box
The alarm horn
Turn signal switch with OBC dim-dip control
Removal of parts
To install the OBC2, the instrument cluster and the existing digital clock from the dashboard have to be removed. When that is done, the knee-cover, steering wheel and the bottom-part of the steering column cover have to be removed. When that is done, the driver’s side looks as follows.
For cars that have the DWA alarm, the relay control box and the secondary wiring loom are not needed. The DWA alarm does have a feature connector for interfacing to the OBC2. The code function does require this connection to activate the alarm horn if the car is being tampered with.
The control-module for the DWA module is located under the knee-cover on the driver’s side (LHD model). Even though it is not required to remove the DWA box, it limits the available working space.
The dim-dip function of the turn-signal switch allows to a sequential selection of the OBC functions. The dim-dip function is not included on non-OBC2 cars and thus has to be replaced unless one wants to push the buttons on the OBC itself.
The installation of the primary wiring loom is rather straightforward and will be integrated in the existing wiring bunch. The green multi-pin connector is for the OBC2 unit; the yellow multi-pin connector for the instrument cluster and the rest of the connector is routed towards the driver’s footwall.
The turn signal switch has a relay integrated in its wiring loom. However, the relay-socket of the OBC2 set did not fit the steering column of #231 so I decided to exchange the wiring looms. Although rather straightforward, the pin-layout of the turn signal switch for the OBC2 variant is different then the part without the dim-dip switch, hence why one has to be careful not in interchange the wiring without noting the connections first.
Although I have a degree in engineering and exchanging wiring looms and the required soldering should be a piece of cake, the primary functions (turn lights, emergency lights and high beam) were tested prior to final installation. The dim-dip switch is tested in combination with the OBC2 unit that should be connected in this stage.
Please note that the coding plug for the OBC2 is E28 M5 specific. Coding plugs for the German version are still being stocked in Munich and are reasonably priced but take a few days to deliver. After testing the OBC2 controls and connection of the gong-speaker, the DWA alarm control box and the routing of the wiring for the ambient temperature sender, the steering column cover and the steering wheel were placed back.
In the mean time, the correct coding plug has arrived and was picked up this morning. When I have replaced that part, I can test the temperature function for which I still have to install and connect its sensor.