Sounds like they have connected the wiring on the switch wrong or they have a short but if the motor will not generate power back to the coil you will always have the problem.
To check with multi meter just put it onto the battery terminal and check you should have at least 13 + volts going back into the battery.
Regards,
Bruce
Please do not PM me asking for support. Post on the forums as it helps all members not just the individual.