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The first step I would take is to load test the batteries, even if they are new, because one or more of them could be defective.

A simple load test, assuming the scooter will not move when throttle is engaged, would be to leave the scooter on the floor, turn it on, fully twist the throttle, and look at the battery gauge on the throttle. If the throttle's green 'FULL' light goes out and only the throttle's red 'POWER' light and yellow 'LOW' light remain on with the throttle fully engaged then the battery pack is dropping too much Voltage under load which is causing the problem. If that is the case then the batteries need to be replaced.

If all three lights on the throttle stay on when the power is on and the throttle is fully engaged with the scooter on the floor then please let me know and I will provide the next troubleshooting step to take.

Interstate battery is a good company so I trust that they properly tested the batteries and they are good. The problem must lie elsewhere then.

Since the motor is running when the rear wheel is off the ground that indicates that the power switch, wiring harness, and circuit breaker are functioning. However I would not rule out a malfunctioning circuit breaker or switch under load though. The first thing I would do is temporarily bypass the circuit breaker to eliminate it being the problem. The circuit breaker can be bypassed with a short piece of insulated 14 gauge or thicker wire with two .250" male quick connect terminals on each end like in the picture below. If bypassing the circuit breaker does not solve the problem then I would reconnect the circuit breaker and use the same jumper wire to bypass the power switch to make sure that it is not causing the problem.

If bypassing the power switch and circuit breaker do not solve the problem, then the issue would have to be with the controller, throttle, or motor. Please let me know if the bypass tests do not help and I will let you know the next troubleshooting steps to take.

The battery power going directly with two lines to the circuit breaker is correct according the Razor wiring diagram.
Here is a wiring diagram for the Razor E325 scooter with the place that the jumper wire goes drawn in orange.

So far the battery pack, circuit breaker, and power switch have been tested and are known to be good. Since the motor runs with the wheel off the ground that indicates that the brake lever switch is good so I do not think that we need to test it.

The only components left to test are the throttle, controller, and motor. The controller can not be tested without having an electronics test bench or another identical scooter to temporarily install it into. However if the throttle and motor test good then the controller could be determined to be bad by the process of elimination.

Testing the throttle and controller require advanced testing methods compared to the other tests we have done so far.

Throttle: To test the throttle a 5 Volt DC power source is needed. It could be a 5 Volt DC wall mount power supply, like the kind used for answering machines and calculators, or it could be three 1.5 Volt batteries wired in series to produce 4.5 Volts. (4.5 Volts DC is enough power to test a throttle.) However do not exceed 5 Volts DC of power to the throttle or it will damage it. Also do not apply reverse polarity to the throttle because that will also damage it.

Working throttles have a power output roughly between 1-4 Volts DC. The output Voltage can be as low as 0.5V and as high as 5 Volts DC on a good working throttle. The speed controller will only read throttle output Voltages between 1-4 Volts DC so if the throttle Voltage is under or over 1-4 Volts DC that is normal and the throttle is good.

During testing slowly turn the throttle to full power and read the Voltage on the multimeter. The Voltage should react proportionally to the position of the throttle as it is being turned. A released throttle should have a low Voltage reading and a throttle in the full throttle position should have a high Voltage reading.

Different versions of Razor E325 scooters were made with different throttles. Please let me know how many wires your throttle has and I will let you know which wire is the +5V input, ground, and output wire.

Motor: To test the motor under load the motor and battery pack need to be disconnected from the controller and a testing wire harness with a heavy duty switch needs to be made. The harness should be made so the switch can be taped to the handlebars so it can be turned on and off when riding the scooter. The testing wire harness will eliminate all components other than the battery pack and motor so the motor can be sure to receive full power from the battery pack. When using the testing harness the scooter should be pushed to walking speed before the switch is engaged to prevent over powering the drivetrain and damaging the motor shaft.

For testing the motor as I described above the throttle should not be connected to the test circuit at all. The throttle could be left connected to the controller or disconnected from the controller for the motor test.

To avoid cutting the motor wires an item # CNX-50 connector could be purchased from us and attached to the test wires. The CNX-50 connector terminals will need to be soldered onto the test wires or crimped onto them using our item # CRM-100 crimp tool. The CNX-50 connector is available on this page and the CRM-100 crimp tool is available on this page.

In my last reply I described how to test the throttle and motor to show exactly what is involved in testing these parts. For someone who only has one scooter to repair, taking the time and obtaining the tools and materials to perform these tests may not be worth it compared to buying new parts and installing them to see if that helps.

Here are the three throttle wires used for testing:

That is a great idea to use .250" female quick connect terminals for testing the motor so you do not need to cut the wires. We have so many CNX-50 connectors laying around here that I never thought beyond using one of them for the test.

The Razor E300/E325 5-wire throttle with power indicators can not replace the 4-wire throttle without power indicators because the 5-wire is a variable speed throttle and the 4-wire is an on/off type throttle. Since the scooter was running for 6 months the throttle and controller would both have to have been replaced with 5-wire versions. It would not cause any issues to replace a 4-wire single speed (on/off) throttle and controller with a 5-wire variable speed throttle and controller as long as the installation was performed correctly. If the scooter worked for 6 months then the parts had to be matched and correctly installed.

I had a customer a few months back have the exact same problem with their Razor scooter with the motor not producing enough power. He replaced the batteries and throttle without any luck. He said the problem started immediately after the scooter had been knocked over and landed on its motor. I never heard back from him so I do not know if he pursued the problem and got it fixed though. If you figure out what the problem is please let me know so I will have a better idea what to recommend to others.

The ZK2430HP-FS controller is an unusual model number. This does not mean anything bad just that most newer version Razor E300/E325 controllers are ZK2439HB-FS or ZX2430D-FS so I do not have a wiring diagram for the ZK2430HP-FS. If the ZK2430HP-FS controller has a 5-wire throttle connector then it is most likely compatible with your 5-wire throttle.

The original type 4-wire throttle and controller are a downgrade from the 5-wire throttle and controller that older version Razor scooters have. The 4-wire throttle and controller is an on/off system with no speed control, the scooter is either off or at full power. While the 5-wire throttle and controller system is an infinitely variable speed control system where the power ranges from off to full power and is adjustable by the throttle to everywhere in between.

Since the motor and batteries are good that only leaves the throttle and controller to be the problem. Typically throttles either work or they don't, as they have a single hermetically sealed IC chip inside of them that controls the output signal. I still recommend testing the throttle to pinpoint the problem though. That way you can be certain that the next part you buy is the one which is defective and needs to be replaced.