Replacing or DIYing alternator electronics lead cap?

[Transit-man-van]

So I have connected everything back up now with my new dc-dc charger and, tentatively, everything looking good!

When I was taking the old alternator off though I got stuck and without easy access to the internet due to lack of electric I called my neighbour over for assistance. He dove under the van and while tinkering around flicked off the cap and I said I should probably see what he did there but he said "it's just a cap".

Turned out my sticking point was taking the belt off which I only found out once I could look on the internet again.

When I then came to try and put the cap back on myself I couldn't get it on! I was not able to get it to clip back on securely. Couldn't be bothered to call him over just for that so I left it in a precarious state and went for a driving and lo and behold it has fallen off.

It is the 3 wire lead which had the plastic cap. I am wondering whether it is essential. I see other electrical leads under the hood with no cap. One does wonder why it was there though and whether to replace. I have some electrical terminal caps and thinking maybe I could split one of those and tape up with some electrical tape.

The bonnet will be shielding from the rain won't it? Maybe it would fly in via the front when traveling.

Thoughts on how essential it is to replace that and if so what to use?