obd2 bench harness

Sloppy Mechanics Bench Flashing harness build sheet and instructions for obd2 (blue red/green) style LS ecu's (and some more)

Bench harness built by sloppy mechanics page member Ben Nichols

If you are competent and just looking for what wires go where, without any filler, skip to bottom


1. 12-19v power supply, 1amp min ( i have used 500ma, but i would recommend staying above an amp)

a. these are very easy to find in old hardware, chargers, external computer components like hard drive enclosures and modem power supplys etc.

b. I have tested 12-19 volts without a problem, that being said i would say closest to 12-14 will should be used since that is what the car uses.

2. GM Blue ECU/ECM/PCM (whatever you want to call it) 80 pin connector.

a. This is what interfaces with the ECU directly, you need this guy.

b. They have 7mm bolt in there, wich is kind of annoying but also nice to make sure you don’t accidentally unplug and brick anything. I was able to hammer mine out to make it easier to fire on and off ecu’s, I would say that’s a personal preference thing and if you are doing volume.

3. In cab OBD2 connector

a. I usually cut mine out of blazers and cavaliers since there are a million at the yard and they are already pinned for GM stuff basically

b. Make sure it has orange black and purple wires, that will make the rest easy

Once you have the parts (assembly)

1. Alright guys, once you have all of that, please take the power supply, strip the wires and test them with something 12v or a multi meter or something so you know that it works, and makes 12v. This may alleviate some headaches for you.

2. Youll flip the connectors wire side to you, on the blue ECU connector pin 1 is un the upper left, and 20 at the end of that row and 41-60 is the bottom row. You’re only using 4 pins, you can leave the rest in there, or de pin them all to clean it up.

3. On the obd2 port, wider side up, wires facing you, that is 1-8 at the top, and 9-16 at the bottom. You’re also only using 4 wires on this connector.

4. You want to take the power wire from your power source, and connect it to Blue 19 and 20, (upper right two pins) and OBD2 port 9 (bottom left).

5. Then you take your ground, connect it to Blue pin 1 (upper left) and pins 4 and 5, (upper middle) on the obd2 connector

6. Now you take the serial data wire, purple wire Blue connector 58 (lower right side) to obd2 port 7 (upper right side)

Now before anything else, plug it in and see if you can access the ecu with whatever you are using on the obd2 side, if you can connect/read/write, you’re set, clean it up if you care and ship it.


12v power to OBD2 pin 9 (orange) and Blue ECU pins 19 and 20 (pink/red)

ground to obd2 pin 4-5 and Blue ECU pins 1

now connect pin 7 (purple OBD2) to Blue ECU pin 58 (serial data line)

you're done.

note pin 60 i am using but it does not need to be used, that was when i was testing and i just left it in there.

same with pin 16 (brown on the obd2) i clipped it out of the yard like that, never unpinned it.