I've got an old MagicShine light, a cheesy eBay Thorfire, and some battery packs. All of them seem to have the same watertight plugs.

What are these plugs called, and can they be replaced?

I'd like to cut the MagicShine cable, make a modification, then put the cable back together. I could resplice the wires where I cut the cable and cover the damage with heatshrink, but I'd prefer to cut off the plug on the end, then replace with a new plug. So it looks factory. Not cut in half and taped back together.

Is this possible? Does it take fancy tools?

The connectors on most powerpacks and lights that use powerpacks are just a waterproof version of the CCTV power connector. It's easy to find but waterproof ones not easy. I've used the standard ones with my DIY bike lights but getting wet where I live isn't much of a problem. It's been nearly 100 days without measurable precipitation. Looks like you could use this one from an international seller for $1.39 a set postpaid: https://www.ebay.com/itm/Waterproof-...GHUEJEjaMyTb_Q

I had a CREEE light that the cord went bad inside the light. I tried to disassemble, but it was sealed, glued together, and very difficult to access the inside. Perhaps more work later.

I've found that plugs are a pain to work with. I think the "Factory" ones are hot molded at the factory and built essentially in a single unit (thus well sealed). If it was me, I'd cut the wires, solder and heat shrink tape the middle.

Do the splice close to the plug and butt the heat shrink up against the plug base. That will look factory.

The plug is called DC5521, according to the electric flow, outer and inner diameter of the plug.
Since there are expansion cables and also y-cables with magicshine-plug, this would be easier.

What modification exactly do you plan to carry out?

There's a grommet hanging on the cable, just outside the aluminum bulb housing. The hole is too small for the grommet so it just sits there useless.

So I have to get the cable entirely out of the way to drill out the hole.

While everything's removed I'd like to take a stab at fabricating a mounting plate that surrounds the grommet hole, taking advantage of the flat surfaces adjacent to the grommet hole. The plate would have two holes. One for the screw, which is only a few millimeters from the grommet hole. The other hole would allow the plate to slip over the grommet and contact the flat surfaces adjacent to the grommet hole.

The electronic puck inside the housing will come loose, but there are two little stripped out screws holding the electronic puck together so I can't get to the soldered ends. The two screws are totally rounded off at the heads so I can't disassemble from the inside out, That means cutting off the plug. Then everything - the puck and what's left of the cable - could come out puck first thru the open face of the aluminum housing.

Maybe I'm reinventing the wheel. Maybe others have figured out ways to improve their MagicShines?

Maybe illustrating your describtion would help to see the whole image clearer

And what exactly do you mean with "improve MagicShine lights" ?

How does a person post a pic? Does the website host images or do you have to post them to photobucket or etc. and link back to the forum?

Go to the "Advanced" editor. Click on the paper clip (attachments) JPG images are best.

OK, here we go. I think I attached a pic. Geez, it's been a while since I used GIMP...

Yay, it worked! The dinky mounting screw sits way back from the light's center of gravity, so there's leverage every time the bike takes a bump. A mount plate that reached over the grommet hole and contacted that extra surface ahead of the grommet hole would be more stable.