I have a 01 ultra classic. At idle bike charges between 10/12 on gauge with my voyage tester attached to battery it is showing 13/14.23. At crusing speeds the gauge on dash goes to 16 check eng lite comes on and it will slowly go down till bike dies. Is this a volt reg prob or a stator prob. I am a mechanic been wrenching on Harley's for years but have no exp on anything twin cam. Due to the cost of parts to repair I cannot replace both at same time or I would do so. Trying to pin point stator or reg. Battery test good at 400 cca as well.