Hi everyone! 

I’m in the process of restoring my 75 DT250. 

Last summer I bought a new 6v battery. It lasted only about a week then I noticed the top of the battery was dark brown and all the wires coming from it had melted! 

I’m ready to start digging in to this again, and now armed with knowledge from this forum, I feel like I know how to proceed. Bar a few items.

I have a voltage regulator ready to wire in. Any consensus, to wire it in by the air box or in the headlight shell like the service bulletin?

The wiring diagram shows a fuse off the battery, which I do not have. Any idea on what size fuse I should use?

As well, the wires of the rectifier look like they’ve taken a bit of heat as well? Should it be replaced?

Pretty sure fuse is 10 amp, but double check in the service manual (see Tech Library).

Yes, replace rectifier. I bought a generic 6v one for my CT1, but kept the mounting bracket from my original one, just to make fitment easier.

I've mounted my regulators around the horn and bottom yoke (aka triple tree) area, just so that I only need short lengths of wire to get to the headlight bowl. 

I'm likely wrong--but sound like it's had a quick discharge, too quick for the wires to handle like a semi dead short.
Alternatively has it been charging too hard & that wouldn't be easy, but if someone had powered the rectifier straight from the yellow & you'd been doing flat out road riding for a distance with headlight 'off'.--so unregulated high charging--i wonder if that would fry the battery & wires by boiling the battery dry.
Was everything DC operating like indicators & stop light, horn, all dc stuff, without the motor running on with new battery when you first fitted it.
I guess nothing was operating in the end, except trying to operate straight off AC from the mag with motor running.
Was the rectifier fried or wires in & out corroded. If that was the case then there would be 'no' charge.
Or had the rectifier shorted back to the lighting coil giving a fast high draw hence frying the battery wires.
For that to happen the fuse would [should] blow--well maybe not as not a dead short through lighting coil just a high resistance.
Has someone bridged the fuse with something to stop it blowing.
I'm full of wild guesses but a regulator is a good idea except check for a short circuit too.
By "75 i'd have thought they were fitted with a regulator [single yellow wire silver tin cover regulator somewhere--under the airbox maybe].
Sorry i'll read your story fully later tonight.
Welcome from NZ if you're new--or welcome back.

Greetings from Tennessee