Starter stopped working

'76 kz400 with electric start, worked since I've had the bike and all of a sudden stopped. Couldn't get the starter to move when arc'ing the starter solenoid but it would move when I put a jump box on the starter itself. So I bought a replacement solenoid and now instead making a weak almost start noise the starter button doesn't generate any reaction from anything. Not sure if I've got the new solenoid wired right as it looks a little different, photo for reference and thanks in advance for any advice.

 

Basically, it is very easy to test a starter solenoid. Of course, you need a Volt/continuity tester.    Believe yellow/red is ground or negative on this 400, and blue/red comes from starter button.  Thus I would check for continuity between Red/Yelow and ground first.....then...   12VDC battery, any battery or 12VDC power supply applied to small wires should make it click(pull in)..... Big posts should read open before applying power, and continuity while under control power and clicking once..   That simple.

Don't see any reason cranking motor would not jerk when "arching" big posts on solenoid, but would do it under 'jump box'.   Of course, this has to be done with heavy gauge cable, like motorcycle jumper cable, and requires a good battery.

I wonder if battery is good, and if so, do you get 12VDC on small wires when you depress the starter button???...also wonder what happens if you disconnect your battery all together and connect leads directly to jump box???  ....respecting polarity, of course.  

Did a little more testing in the meantime, checked the starter button end of things and am getting a 6 back on the meter. Don't have a battery tester but ordered one, pretty sure the battery is good though. It's a year or two old AGM and has been on a smart trickle charger showing it's fully charged (headlight lights up fully when key is on too) 

In the pic your meter appears to be set to ohms and not volts? It is not ohms but rather voltage from the starter button to the starter relay that allows battery voltage to be passed to the starter.

I should qualify that I absolutely despite volt meters and all of that stuff, I don't understand how they work and no amount of anyone explaining it has helped. I just want to launch them into the woods or the nearest fire everytime I see one.

That said I can repeat that test if it'll help on the correct setting or just wait for the battery tester that's coming tomorrow if that's the right next step.

Thanks for the help.

Those MotoBatt batteries 100% suck since they started making them in CHINA. They were once a really good brand with the strangest connections ever but now they are simply shite 100%.

Always always always try a new battery first.

i know photos can be deceiving.
Just make sure there is enough distance between these two wires.
Otherwise, you will have one powerful toaster.
i would put electrical tape or heat shrink on the solenoid terminal.

My guess echos the above comments. It sounds like your battery may be weak. Your starter should fire if you short the studs on the solenoid. You could have bad wiring going to the starter, but check the battery first.

In fact, your old solenoid may be fine.

Sometimes things aren't always what they seem. You have a gear reduction starter, have seen plenty of those fail. Honda twins used similar also. You say it previously worked but doesn't mean it still is. Does bike still start with the kick starter? Here's a kit Kawasaki sells for those starters. Also make sure your starter sprag clutch isn't locked-up! If for whatever reason it has became locked it's going to be spinning the starter motor all the time, even after start button is released. If locked, you over rev the armature in starter to speeds it wasn't meant to handle. The Kawasaki KZ750 Twins suffer from this and it is common. Those OEM solenoids are pretty robust, if working, better used then the 15dollar Chinese one you purchased. Do a little research on how to use that Fluke VOM. Invaluable and easy to use diagnostic tool once you get the hang of it, well worth the continuing education time you'll invest to study it's capabilities!      

If electrics aren't your bag you may find my guide to electrical diagnosis helpful. The link to Wiki is in my signature (towards the back of the guide there is a flow chart to diagnose starter circuit problems)

Ok, catching up to the comments here as I gave up yesterday and stacked firewood instead.

The bike worked fine, previously, would start with a kick cold and starter button after that without issue. Tried arching the starter solenoid before taking anything apart and didn't get the starter to react in doing that. Used a auto battery jump box connected directly to the starter and got the starter to spin so I don't think it's anything to do with the starter. The battery is what was suggested by a local vintage moto mechanic and hadn't given me any trouble at all, including the handful of rides I've taken already thus spring/summer. The battery ground wire is only close to the solenoid wire because it's apart and I was trying to get everything in one photo without any help but understand it should be tucked away from that once I button it up.

Battery tester coming later today and will share the results but for now the battery is reading full green on my smart trickle charger (NOCO Genuis1).

Ok, new battery tester acquired and results are bad battery to my surprise. Looked it up and I apparently bought it Jan '24 and don't exactly daily drive it so I guess that's the culprit and the rest of the parts were probably fine. Charging up and old battery to see if that's still any good, otherwise I'll be buying a new one. Any suggestions?

Photo of test right after I took it off trickle charger for 2 days.
 

I have had excellent results with Interstate AGM batteries. In my ZRX, they last 9 or 10 years.