I'd suspect it was an installation mistake that caused this mess. But if he wants to claim a defective part, that's ok - he can go after the part outfit he used. However, the bottom line is you should not be paying a cent for this repair. Make it clear that you will take him to court for full reimbursment if he makes you pay anything to get your vehicle back. And keep going back until it's running as well as before all of this happened.