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IIRC there should be two bolts under the back end of the seat and two more in front of the back wheel.

The fun part is you can use the bolts under the seat to mount the taillight assembly. The brackets would be pretty easy to make and it won't matter if they don't look great because you won't really be able to see them. Ideally you'll have (or can acquire) a vise, a torch, and metal-bending tools for that.

For mine I used 3/4" wide x 1/8" thick mild steel from Lowes or Home Depot, but started with 1/2" x 1/16" aluminum so I could bend it by hand to make a prototype. In your case you could have the brackets come out under the back end of the seat and go vertical to hold the taillight assembly in place. This would allow you to use the seat hinges as normal.

Ya, looking at the photos earlier I can see the bolts under the seat, just figured they were also holding in other things so I'd have to figure that out if I just took the whole thing off.  Leaning towards just cutting shorter both the front and rear fenders as it seems less likely for me to mess up anyway and i can figure out some way to add a strip light on the rear or a brake light that's meant to tuck under the lip of the rear fender and then use the stock signal mounts for new rear lights.  Will say it's feeling like chopping the frame might just be simpler but might just give this a shot first and see how it goes I guess.

Took a bit and I've a stack of parts to return to Amazon but this light actually matches the arch of the rear fender almost perfectly 

MotoParAcc Red LED Tail Light, Universal Motorcycle Brake Taillights for Harley Dyna, Road King,Yamaha, Suzuki, Dirt Bike and ATV a.co/d/atrCQM9

Only thing I'm on the fence about is how to mount it as it's get studs that point straight out the back and I'd need to either make-up a bracket and either expoxy it to the underside of the fender or just epoxy the light itself to the fender. Any idea which would work better?

Pics for reference, also does anyone have an idea of what aftermarket fenders fit? Or can you just go without a front fender? Was pondering that but was concerned about the brake lines.

ThatYeti wrote:

Pics for reference, also does anyone have an idea of what aftermarket fenders fit? Or can you just go without a front fender? Was pondering that but was concerned about the brake lines.
 

The OEM front fender includes a heavy(ish) middle bracket that serves as a fork brace. Without that, the front end will feel vague and wobbly and the handling will suffer... as I discovered when I put a Ceriani fiberglass front fender on my '79 KZ400.

Cut the OEM fender or paint it or whatever, but keep the fork brace portion. Keep in mind, too, that the fender is there for a reason: it prevents some dirt, etc. from hitting your engine and exhaust.

That was where I had tentatively landed on the front fender, was just hoping to find one that would bolt in so I could avoid having to cut into it.  Any idea if the plan for the rear and break light seems reasonable?

ThatYeti wrote:

That was where I had tentatively landed on the front fender, was just hoping to find one that would bolt in so I could avoid having to cut into it.  Any idea if the plan for the rear and break light seems reasonable?
 

The KZ400s were designed and sold as basic commuter bikes; there isn't really a lot of aftermarket support for cosmetic things like fenders, especially now that the 400s are over 40 years old. However, that gives you the freedom to do more or less what you want.

That taillight shouldn't weigh very much so I think epoxy (assuming JB Weld or similar) would work. You will want to take a Dremel-type tool or an abrasive stone in a drill to remove the chrome plating where the epoxy will go. JB Weld requires a roughed-up surface for adhesion and I don't think it will stick well to chrome. (Removing chrome with sandpaper can be a big PITA and I don't recommend it.)

Depending on where you live and how strict the safety inspections are, you might be required to attach the brake light with actual threaded fasteners. You may want to clarify that before you commit to a path.

Bear in mind that once you breach the plating the fender will be more susceptible to rust, so try not to leave any bare metal exposed - touch it up with black paint or something.

Thanks and I've an idea of what I'd want the fender to look like, just hate cutting stuff is all; but will have to give it a go once I sort out the rear.

No inspections once I got it registered so wouldn't need to worry about that, was more thinking about if it ever got broken and I needed to replace it; I'd have a much easier time if the bracket was epoxy'd rather than the light itself more than anything but that's putting a lot of faith in my ability to make a bracket.  Guess the underside of that fender is either dirty enough or has already bene painted so I didn't think about the chrome adhesion issue but it's a good point that I'll keep in mind regardless of which direction I take.  Thanks for the thoughts on all this.

Here is what I did to mine. Seems to be the same light you got.
 

Looks identical actually, what did you use to mount it?

Also are these bullet connectors I can just pull apart? Waiting on rubber seals for the wiring pin connectors coming tomorrow then plan to tear into this little project.

ThatYeti wrote:

Also are these bullet connectors I can just pull apart?
 

Yes, but they connect pretty firmly *and* they've been connected for a long time, so they may not come apart easily. Be sure to hold the connectors on each end rather than pulling on the wire itself. If you have some shrink tubing handy as a replacement, you can cut the protective cover off and get a good look at the connector before you take it apart.

Surprisingly managed to find a matching wire pin connector to line up with the one the light came with but cannot for the life of me find the rubber seals to match. Already tried 18, 20, & 22 gauge and they're all too big.

Any idea what size I'd need and where to find them?

Otherwise, would running it without would cause any issues?