FLHTC charging system trouble

1985 FLHTC with new stator and regulator putting out 14.15 at idle then turn passing lights on and it drops to 13.77. When charged the battery is reading 12.7 before a trip. If I ride with passing lights on the battery looses enough volts to start. But if I turn off passing lights and let her get charged she will start. This is a one year old maintenance free battery and kept charged with trickle charger. Any thought why this is happening would be appreciated. TIA

have you checked the battery voltage with engine running after long ride with lights on? Have you checked your major ground connections? sound like a problem you have been pursuing. does it not want to crank like the starter is drawing heavy? can you get the battery load tested, all most new can bite hard sometimes. try to give us more info if you can so we can assist further.

30 year old bike with 30 year old wiring? Get a wiring schematic, check and clean ALL ground points (remove wire, clean point, reattach firmly) would be my first action. May be the cheapest fix. Take battery to a battery supply store to check electrolyte and for a weak cell would likely be my second action.

What amp charging system did you get.

You can do things to have less draw on the battery like HID headlight & all.

I went with a stock rated charging system. Since I am tearing down the top end to fix a FEW oil leaks, I will follow each wire and clean them up. With a confirmed termination point I can then address this situation. I do have the HID headlamp and thinking going to LED bulbs.