Question on Battery Replacement and Battery Tender Installation

My son has a 2010 mini, and today we were installing an amplifier for a subwoofer in it. At one point I disconnected the battery to connect the power wire. Long story short, we didn't get the amp working, but now the car is idling funny, the power steering keeps going in and out, speedometer stopped working and pretty much every warning light on the dash is on! I don't understand how losing power could do all that. Do you think it's a coincidence? I've read that they have problems with the power steering pump, and when we took it to the parts store, one of the fault codes said it was an intermittent speed sensor failure. He thinks I did it, but I have no idea how I could have done that. Do these cars have issues with faults when you replace the battery?

__________________
This post was auto-generated based upon a question asked on our tech article page here: MINI Cooper Battery Replacement and Battery Tender Installation (R50/R52/R53 2001-2006) | Pelican Parts DIY Maintenance Article

[Nick at Pelican Parts]

You probably caused a short while working on the vehicle. Either blowing a fuse or damaging a control module.

I would start by checking the vehicle for fault codes. If the system is not working properly, a fault code will be set. This will be your best bet when diagnosing.


- Nick

[Luccia at Pelican Parts]

And as another idea, MINI's do some weird things with a bad battery so maybe the disconnection is showing the batteries true colors and it's on its way out. Wouldn't hurt to test the battery to see what condition it's in, especially if it has never been replaced before.