Fabricating an OBDII to OBDI Harness Adapter Plug
I have made a successful OBDII to OBDI adapter plug that allows me to run an OBDI (S13) ecu with a factory OBDII (S14) harness. There is no cutting of the factory OBDII harness necessary and the result is a plug-and-play application.
This write-up will cover the process of making the adapter plug. I'd say the level of difficulty is moderate--especially if you are inexperienced with soldering--so leave yourself some adequate time to build the adapter if you are not proficient with electronics.
First off, here is a list of necessary parts, materials, and tools:
-An OBDI engine wiring harness. This can be from any 91-94 Sentra 91-93 NX, 89-94 240SX, 90-94 Pulsar GTi-R, 93-94 Altima, 89-95 Bluebird, or 91-93 G20. It does not matter if it came out of any of the aforementioned cars equipped with a 1.6, 2.0, or 2.4 because the ECCS plug is all you need off of it.
-An OBDII ECU. This can be from any 95-99 Sentra, 95-98 200SX, 95-99 Altima, 94-96 and 99 G20, or 95-98 240SX. Again the type of motor in these vehicles is insignificant since the plug is all that is needed from the ECU.
-Phillips and flat head screwdrivers.
-Dykes.
-Needle-nose pliers.
-Wire strippers.
-Soldering iron (pen style preferred) and solder.
-Solder remover (optional).
-Masking tape (optional).
-Electrical tape or shrink tubing.
-Two part epoxy (and lots of it).
-18 or 20 gauge wire.
Use the following pinout diagrams and excel spreadsheet for this buildup.
click here for the pinout!!
Please note that this Excel spreadsheet does not provide for the wires on the CONSULT data link plug. I did not need my CONSULT connectivity so I did not research it. However, there are people currently researching this and as soon as I have a definitive cross-reference, I will add it to this write-up.
The Process
Start by removing all the factory tape and loom from the vicinity of the ECCS plug on the OBDI harness.
Now you will begin cutting the plug from the harness. In the event that you want to possibly re-install the plug at a later date, number each wire with masking tape according to the pinout diagram before cutting it. This way, there is no question as to where the wire was pinned. Be sure to give yourself a sufficient amount of lead wire.
Now it's time to get a plug out of an OBD II ECU.
Remove the ECU from its mounting plate and remove all screws from the outer casing, on top, on the sides, and on the bottom. This frees the circuit board from the case so you can remove the plug.
Now on the bottom of the circuit board, there are seven screws that need to be removed. Three of the screws go through the plug. These three screws have solder in them and can be removed one of two ways. If you have a solder sucker, remove the solder with that and simply unscrew them. However, if you are like me and do not have a solder sucker, these screws are quite simple to drill out.
Once the circuit board is free from the case, clip the wire that connects it to the body of the case.
You will see that on the back of the plug, there are pins that ninety down to the circuit board. Each pin is soldered to the board. If you have a solder sucker, you can use it to remove the plug. Once all the solder is removed, the plug will lift right off the board. However, if you do not have a solder sucker (like me), then you must clip each pin. The idea is to leave as much length on the back of the pins as possible, this will make soldering lead wires MUCH easier.
The easiest method when you are clipping is to remove any pins that you do not need right after they are clipped. This way you have more access to the trickier pins on the bottom of the plug. What I did was print out the OBDII pinout and black out the pins that I did not need (reference the Excel spreadsheet for this). This way, it was an easy visual reference. After snipping the back of an unneeded pin, simply bend it as straight as possible and pull it from the plug with needle-nose pliers.
When you are finished clipping all the pins, the plug comes right off. Here is a picture of the back of the plug.
Now your plug should have only the pins necessary to run the OBDI ECU. It is time to solder lead wire to each pin. 4-6 inches of lead is sufficient for each pin. This is kind of a tricky and time-consuming process, so be patient and take your time.
When you are done with all the leads, make sure to pot the plug with a 2 part epoxy that dries very hard. The solders on your leads will most likely not be extremely sturdy and the epoxy will ensure that the wires never seperate from their respective pins. Dam the plug up with whatever materials you have at your disposal which will do so and pour in the epoxy. You will use quite a bit of epoxy for this so make sure you have a lot. You may also want to block off the large slots in the plug so epoxy does not run down into the area where the ECCS plug connects. When you are done, it should look similar to this:
Next, it is time to connect this plug to the ECCS plug that you cut off of the OBDI harness. Using the pinout diagrams and the spreadsheet, connect, solder, and tape or shrink tube all of the wires to their respective "partners." Note that pin 50 on the OBDII plug connects to two wires on the OBDI plug. The (spl) in the spreadsheet means "splice." Note also that pin 45 may be missing from your OBDI plug, in which case you will have a leftover wire on the OBDII side. This is not a problem. It is easiest to do this wire soldering one side at a time.
When you are done, your plug should look similar to this:
Congratulations, you are done! It is plug-and-play from here. Simply plug your factory harness into the OBDII side and plug the OBDI side into your OBDI ECU.
S14 to S13 ECU conversion harness rewire –
Originally Posted by Spinks
