Hi,
I want to direct your attention to item 60 in the link below and the reference, in bold type,
F-10directly below it.
That wire is called a "bonding.strap" by electrical engineers.
Buy OEM Parts for Honda Outboard 40HP POWER TRIM & TILT Diagram
www.boats.net
If you look into the lower right corner of that page you will see
the page identifier code number
ZW34F1120E. As a result, Honda parts "shorthand" refers to that page as
F-11-20
Now take a look at item 30 in the link below. Note that it is the same wire referenced in the above link and it is attached to the stern bracket in conjunction with a metal anode. Below that are two references, again, in bold type,
F-11-20
referring you back to that page.
In the lower right corner of the page is the page identifier ZW34F1000D or
F-10 for short.
Buy OEM Parts for Honda Outboard 40HP Stern Bracket Diagram
www.boats.net
Ok, so I tell you all this because that bonding wire was put there...as it is on many, many outboards....to help with damping stray electrical currents causing electrolysis which results in galvanic corrosive destruction of metals.
In addition, the zinc anodes are there for the same reason.
The condition of that wire and the anodes, as well as how effectively they are attached to the outboard can impact how much corrosion is taking place and might have been a factor in what's happened to your 40.
While the wire conducts current, the zincs are "sacrificial" metal intended to corrode instead of other metals.
But if either one isn't attached correctly or is corroded too much the water and air will attack the other metals on your outboard.
Thought you'd want to know if you don't already.