Crazy Electrical Issue

[Mcgeeclan]

2008 M35. 145K
Starts out with the BATT light and the BRAKE light coming on. Then a while later the radio shuts off, then the VDC, SLIP, ABS and TPM lights come on, then the speedometer drops to zero even though I'm still driving. Then the engine loses power although it is still running. Then the seatbelt shoulder harness tightens up pulling me back into the seat. The alternator has been replaced 3 times in the past 12 months.

Does anyone have any ideas what to be looking for?

[VStar650CL]

That certainly sounds like the alternator output fell off and then the battery ran down to where the car couldn't run. So it's likely you have another bad alternator, the question would be why. Check voltage drop between the alternator case and the engine block to make sure you don't have a rusty bracket or something which is heating up the voltage regulator from poor grounding. Your M also has the "smart charging" setup which we know will get stupid if the Battery Current Sensor starts lying to the ECM. That can cause cyclic undercharge issues which can eat up both batteries and alternators, but it's easily mitigated by clipping the smart charge wire between the IPDM and alternator (topic623786.html). Lastly, you could have a wiring issue in the alternator field circuit. Back-probe the Light Green/Black wire at the alternator and check voltage drop to the positive battery post. It should be very small, probably under 100mV. If it's higher you may have a bad wire or connector causing bouncy alternator output and making the units run hot.

[Mcgeeclan]

** UPDATE**
I connected a digital multimeter to the battery terminals and mounted it on the dash so I can see what is going on.
Here's what is happening.
Before I start the engine the voltmeter reads 12.5V +/-.
After I start it the reading holds steady at 14.5v +/-.
After the BATT symbol and the BRAKE light come on it still maintains 14.5v +/-.
After a while it jumps up to 15, then 16, and then read 17.5v +/- and that's when all the crazy lights come on. etc.
My question: Is the caused by a bad alternator (voltage regulator), or is something else causing the voltage to spike?

[VStar650CL]

That's a bad regulator, nothing else can cause overvoltage like that. Around 16.8V is usually where the CANbus starts to die and devices stop hearing one another, so that makes perfect sense with the lights and behaviors. Replace the alternator.