1974 merc 850 cdi box melting

[yourbuddymike]

i have a 1974 merc 850 that runs great and all the wiring seems correct and everything works as it should except that the cdi switchbox get hot enough to melt that black gooy stuff. hoping someone might know what is causing this.

[boats.net]

That's not uncommon we see a lot of the older switch boxes with the potting material melted but switch box continues to work ok.

[yourbuddymike]

Thanks for your reply. In that case, i'll just keep running her until she won't.

[Jkelly]

Have you changed out wire harness. I ask because I am rebuilding a 1978 Mercury 115 and I recently purchased a new wire harness and the wires are significantly thinner than oem. Makes we hesitant to make the swap. It seems like the thinner wires might make things get hot

[boats.net]

Thinner wire shouldn't be a problem unless it's the main Battery positive and negative wires they shouldn't be smaller gauge wire then OEM.