2017 Tohatsu MFS30 - Rectifier Fuse Blowing

I’ve been reading other helpful posts on this site which are relevant to my issue but am still struggling to diagnosis the problem.

In short, I have a relatively new 2017 Tohatsu 30 hp outboard. I recently installed a battery on/off switch. The engine worked fine my last two or three trips but now the 20 AMP rectifier fuse blows when battery switch turns.

I disconnected the rectifier and power went to the engine without the fuse blowing (h/t to this forum for the troubleshooting tip). The fuse blows when I reconnect the rectifier.

My only thought is I possibly damaged the rectifier when I installed the kill switch - but then I’m not sure why the boat worked fine for a few trips post-installation.

Any additional troubleshooting tips before I give up and take it to an expert for repair? I’d certainly appreciate any help.

Year is irrelevant on these; I assume your model is MFS30C.

The only time I ever saw one of these fuses (the only one on the motor) blow was when soemone connected the battery backwards. After correcting the battery and replacing the fuse, all was always OK. The fuse saved the rectifier/regulator.
Assuming you have electric start, the motor will not start if that fuse is blown.
What method did you use to disconnect the rectifier/regulator? If you just disconnected the red wire to the fuse, you may have coocked the rectifier/regulator, although I have never seen that on motors of this vintage.
If the fuse blows every time you turn on power, is the wiring accidentally reversed?

pvanv said:

Year is irrelevant on these; I assume your model is MFS30C.

The only time I ever saw one of these fuses (the only one on the motor) blow was when soemone connected the battery backwards. After correcting the battery and replacing the fuse, all was always OK. The fuse saved the rectifier/regulator.
Assuming you have electric start, the motor will not start if that fuse is blown.
What method did you use to disconnect the rectifier/regulator? If you just disconnected the red wire to the fuse, you may have coocked the rectifier/regulator, although I have never seen that on motors of this vintage.
If the fuse blows every time you turn on power, is the wiring accidentally reversed?

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Thank you so much for your response! I disconnected rectifier at the white tubular connector (which did have red wires on both sides) connecting the rectifier to the fuse cable.

When disconnected, the engine receives power. The fuse blows when I reconnect the rectifier with the fuse cable.

I am going to double check all the connections to make sure nothing is reversed.

Thanks again!