I have written many blogs about 24v swapping our E30s, and for good reason. This is a very popular swap, and a great marriage of two different generations to give "God's Chariot" a little extra oomf.
This blog is going to be about getting your CEL (check engine light) to work on OBD1 swapped E30s. Keep in mind, if you can, I would encourage you to go OBD2, but I understand the simplicity and money savings of swapping in an OBD1 engine.
With OBD1, we are unable to hook up a computer scanner to check codes, but that shouldn't stop you from seeing what is wrong with your engine. The OBD1 BMWs, have a "stomp test" function that can be performed to read your check engine lights.
But before we can even perform the stop test, we have to let the gauge cluster know if there is a problem. To do this we have to run one wire from the DME to the C101 connector to let the gauge cluster light know if there is an issue. Even though I encourage everyone to get comfortable with automotive wiring, I know it is not for everyone, so here it is. If you would like to download free BMW wiring diagrams, visit our other blog:
Download Free BMW Wiring Diagrams
As stated above this will only work for OBD1 swapped E30s using a Bosch 413 or Bosch 506 DME.
The gauge cluster light gets its signal from the DME at pin number 8 on the E36 DME.
You will need to run a splice or tap from this wire to the E30 side. Lets take a look at the E36 DME connector to show you were pin 8 is:
After you figured out the E36 side of things, you will need to fish that wire through to the C101 connector of your E30. Keep in mind this is only for later model E30s with the round C101 connector, not the square. The C101 connector is located besides the fuse box in the engine bay on the firewall.
From here you will have to splice into pin number 12. Here is a layout of the C101 connector
After all this is accomplished, the CEL in your gauge cluster should illuminate if you have an engine fault code. To check and clear the code you will need to perform a stomp test.
BONUS
On a M50 swap in my 1986 325es and it's a little different than described above. The '86 still has the round C101, but no wire in it for the CEL (since they didn't actually have a functioning CEL from the factory). However, behind the instrument cluster the bulb for the CEL is already installed and has two male spade terminals. So, I cut the Grey wire coming from Pin #8 out of the main DME plug (X6000) a few inches past the connector inside the glovebox and ran it straight to one terminal on the CEL bulb behind the cluster, and the other terminal gets wired to switched 12v power. In this case, tap into the cruise control circuit for switched power in the footwell under the dash if your car has the cruise control deleted in the past and the connector is floating around unplugged. If you do not have this, there are other 12v switched power supplies.
