The wires are going to the correct terminals on the batteries. However I notice that the wire terminals are red which are for 22-18 gauge wire, and the MX350 battery harness wires are 14 gauge, so the wire strands should have been too large to fit into the red terminal's wire crimping area.
I would take the red tape off of the wires and terminals and try to pull the wires and terminals apart to see if they are well connected. If they are well connected then the following test procedures can be taken. However, before the bike is put into use I recommend replacing the red terminals with blue terminals so the right connectors are used with the right wire and you know the crimps are safe and will not come apart.
The following testing procedures will require a multimeter.
The first step is to test the fuse between the two batteries just to make sure that it is good and did not blow. If it tests bad then replace it with a new 30 Amp ATO or ATC fuse.
The next step is to unplug the battery pack wiring harness from the main wiring harness and test its connector terminals to make sure they have Voltage. This will indicate if the harness has power and how much Voltage is in the battery pack. There should be around 27 Volts at the battery wiring harness connector terminals. If there is no Voltage then the harness needs to be checked for continuity and the batteries checked for individual Voltage levels.
If there is Voltage at the battery pack harness connector terminals then plug it back into the main wiring harness and unplug the main harnesses other connector from the controller. Then with the power switch on, test the Voltage of the main harnesses connector terminals. They should have the same Voltage as the battery harness connector terminals. If they do not have any Voltage then the switch is bad and needs to be replaced.
These tests should help point to what is causing the problem. Please let us know how it goes.
To answer your question we carry Razor MX350 power switches which are our item # SWT-165 for version 9-32, and item # SWT-105 or SWT-105 for version 33 and up. They are available on this page: www.electricscooterparts.com/razormx350.html
However replacing the switch may or may not solve the problem. I will explain more about this below.
If the light in the switch does not light up that does not necessarily mean that the switch is bad. The switch could have a burned out lamp or may not be getting negative power from the charger port supplied to it, so the light does not glow, however, the switch itself may still be good and turn on and off the power to the bike.
I failed to specify in the previous testing directions to test the thick red and thick black wires in the main wiring harness's controller connector. A test of the thin red wire and thick black wire does not indicate if the switch works or not.
If you got Voltage at the main wiring harness's controller connector thick red and black wires then the switch is working as far as turning the bike's power on and off.
I recommend, with the power switch on, to retest the main wiring harness controller connector's thick red and black wires for Voltage.
If you get Voltage at the thick red and black wires then the power switch is working even if its light is not glowing. And if there is no Voltage at the thick red and black wires then the switch is faulty.
If it winds up that the switch is good other than it not lighting up then please let us know and we will be glad to provide further testing directions.
If these terminals have Voltage when the power switch is on then the switch is working, and if they do not have power when the power switch is on then the switch is faulty.
Please let us know how it goes and we will take it from there.
My mistake. For some reason, I thought you had a version 32 and under, however, you instead have a version 33 and up. Please disregard the previously attached wiring diagram. Here is the correct wiring diagram for the version of MX350 that you have.
If you are getting Voltage at the connector on the wiring diagram called the 'Battery Connector" then we can move forward with the troubleshooting. The Voltage at that connector should be around 27 Volts.
Since the light on the power switch is not lighting up that is a strong indicator that the power switch may be bad. To test the power switch follow the direction in the drawing below.
If the switch tests bad then it needs to be replaced. However, if the switch tests good then please let us know and we can continue troubleshooting without the need to replace the switch.