1986 vro90 hp keeps blowing out port side power box. need elec wizard

[neversinksmith]

new to me 86 evinrude vro90 v4 90hp outboard. no spark on 2 port side cyls .took the box off the other side (it has 2 power boxes, one for 2 left cyls and one for 2 rt cyls) and plugged it in and I had spark so I got a used power box installed it and had spark on all 4 cyls. a few days later I went out to fire her up and it was smoking like a sob so I checked for spark and again ive got nothing on the port side. fried power box on that side. has anyone had this experience? where do I begin? I don't want to keep throwing $50 power boxes on it if theyre only last a minute or two.
what do you think? thanks guys

 

[Faztbullet]

A bad coil can cause this....

 

[neversinksmith]

A bad coil can cause this....

so a coil could be bad yet still allow a spark? when I replaced the power pack on the left side originally, I had spark on all 4 cyls.

 

[boobie]

Any stray 12 volts on the black/yellow wire to the pack could also cause it to blow.

 

[neversinksmith]

Any stray 12 volts on the black/yellow wire to the pack could also cause it to blow.

how do I determine "stray volts"?

 

[boobie]

With a volt meter hooked to the black/yellow wire and the motor not running.

 

[boobie]

Should add, with the key turned on.

 

[neversinksmith]

just so im clear, im looking for continuity between black and yellow wire and a ground? if I have that then there is an issue?

 

[boobie]

No. You're looking for 12 volts D.C. on it.