Merc 18xd switchbox ?

[BLM762]

I just picked up an 18xd and only have spark on one cylinder figured out my switchbox is bad by pulling one off my 9.9 Merc
My question is the Merc part # is 339-7542a19 I found an OEM one for fairly cheap but it is an a21 far as I can tell only difference is the length of some wires is this true or is it the wrong one
Thank you

 

[oldglastron]

Good info on CDI Electronics website, this may help answer your question. you can also cross reference the part number.

 

[BLM762]

Checked it out looks like it will work part number on several places says it could be replaced fingers crossed

 

[BLM762]

I think the a21 is for a 35 hp outboard anyone know how it would affect on an 18hp don't know how the cdi boxes work
the wires are longer and not sure which black/yellow goes to the stater

 

[BLM762]

can someone please tell me or where to look which black with yellow strip goes to the stater and which black with a yellow strip goes to the kill switch
there is a short black/white and a short black/yellow im thinking stater on those then the two brown and one black/yellow are way longer in heat shield does that one go to the kill switch
or does it matter which black/yellow goes to the stater just don't want to mess something up
please help

thank you

 

[schematic]

Makes no difference. They are common in the pack

 

[BLM762]

awesome thank you schematic