Sound like the same problem I got going on a AC 400 manual no power to key but I have power from battery + to solenoid but no power to starter wire on the bottom. A few people says no power will go past the solenoid if it is bad everything at is point to me looks like the solenoid is bad I am going to try one and let you know because it called a starter relay one wire from battery to solenoid and the other wire goes to starter
A bad starter solenoid causing your problem of getting power to the ignition switch is about as rare as being struck by lightning in the dead of winter. Could happen, but I doubt it. In your case there are other potential problems that are far more likely that could cause your issue. You might of read about the "Five Wire Splice" if not Search for it. It's been the cause of many no power issues identical to what you are seeing. Also read this link, explains how it all works Completely dead!
The starter relay or starter solenoid as it is usually called is really nothing more than a simple momentary On/Off switch. It is momentarily on when you press the start button to crank the engine over with the starter motor. That is the starting solenoids primary function to turn on and off the starter motor. That's all it does really. Nothing magical or mysterious its just a switch. However the battery connection on the solenoid is often used to connect the ATV charging system and switched ignition to the battery.
There is a big wire from the battery, (IN). Sometimes labeled (Batt or B)
There is a big wire to the Starter, (OUT). Sometimes labeled (Start or S)
The next 2 or 3 wires may be part of a plug in connector and there may also be a 30 amp fuse on the solenoid (old models)
There is a small wire in (control) often green. There is Only power here when you press the starter button
There may be a small wire often red or orange wire (ignition power)
optionally There may be a ground wire. usually black
These one or two smaller wires may be in a connecter plug on the solenoid or single wires sticking out from the body.
Normally there is power all the time on IN wire and there is power at the big OUT wire only when the start button is pressed when the ignition turned on. This momentary control of this on/off function of the solenoid is controlled by the third wire usually the green control wire. A forth wire small, sometimes red or orange is usually internally connected
to the (IN) wire of the solenoid. This is how the ignition switch gets it power and how power from the charging system gets back to the battery. This is just a feed through just a method to connect the atv's ignition and charging wiring to the battery. Installing a replacement solenoid backwards can prevent the ignition switch from getting power. (I've seen this a few times when somebody has replaced a solenoid but would NEVER happen on its own)
There may also be a ground wire. Does the solenoid on your atv have 3 or 4 or 5 wires? same colors? Check the wiring diagram for your year and model. Starting solenoids are quite durable and when they cause problems or are bad is is usually a problem with turning or cranking the starter motor and caused by the contacts are pitted and not delivering full amperage through the contacts to turn the starter over or is operation gets sticky and erratic.
Just to cover all possibilities for different brands and models or years. On some models there may be only 3 wires at the solenoid, two BIG wires, In from battery and Out to starter and a small control wire from the start button. If it is like this then there is probably a small red wire connected to the POS battery terminal together with the Big red wire to the solenoid, It would be through this small red wire at the battery is the feed to the ignition switch or charge to the battery.
And just to cover all possibilities......
You Cat is equipped with a neutral start safety. Meaning that the ATV must be in neutral or the brakes applied before the starter button will work. Problems with the circuitry that reads the shift lever position or the brake applied switches can keep it from starting. Also problem with the circuitry in the safety kill switch on the handle bar will also keep it from starting.
It could be broken or shorted wiring, it could be corrosion in a connector, it could be bad relay it could be a bad gear position, brake, or kill switch. Trouble shooting this would require you to get quite intimate with the wiring diagram and using a volt ohm meter to troubleshoot it out bit by bit, circuit by circuit. In my opinion this not a recommended task of you are limited in knowledge reading wiring diagrams and using a volt ohm meter. Sometimes a person can get lucky and find an obvious cause like a broken wire or by replacing a bad relay though.