Hi guys, new here! I've read the post on this before but still not sure, so I figured I'd make my own post! I picked up a 1988 formula 242ls, got a killer deal on a 502 mag mpi. My problem is the wiring!!! The boat instrument cannon plug has the 9 pin plug with the 3 big pins! The engine side plug had the 10 pin plug ( with 9 really ). I'm trying to keep the harness the same in the boat without switching it out! What's the best way to do this?? Thanks and glad to be a part of the site

http://bpi.ebasicpower.com/pc/MER84-866337T01/MERWH

Is this what you need? If this isn't it, explain it better and I will try to help

*note that is a 14/10 pin with 9 actual conductors

No I'm going from 9 to 10

i should plug in...

http://bpi.ebasicpower.com/pc/MAR6199-02-06/MERWH

I don't know if they make that adapter. You may just need to change the plug on the engine to match the plug you have on the boat (basically replace the harness on the engine). The link to the wiring diagram is on the site I linked. I have done this many times and it is straight forward.

Sometimes the 10th pin is only the trim indicator wire. Some are wired directly to the gauge and others through the pin.

I'll see if I can find a schematic.

Edit...
As stated below the extra pin is called the data line. It should be brown/ orange in color.

It will plug in. Newer harness on boat side won't plug into older engine, but the older boat harness will plug right into the newer engine harness. The extra pin is for the alarm. After 1990ish it was integrated into the plug instead of going around.

It won't plug in from the bigger pin

Yeah it is orange

They all have the orange wire. That's power feed to the ignition switch??