Strange Problem In my TBTS

One month back my TBTS showed a strange problem, after riding 25kms with head lamp on, and slow down the vehicle with both clutch and brakes are applied headlamp goes little dim but strange thing was engine was running in idling rpm but RPM needle goes down to zero, especially it happens when I try to descending in mud road, if I stop the vehicle completely and checked the needle it was still in zero it goes up only by switch off the head lamp or by revaluating engine hardly, starter motor also does not crank smoothly. So, I checked the battery voltage, it showed 11.60V after starting the vehicle it goes to 11.9V and if I race the engine to 3000 RPM then it will reach up to 12.6V maximum, and if head lamp on then it was 11.8V to 12.4V. According to the Royal Enfield it must be between 12.2 to 13.5 @3000 RPM. So, I think that it was battery problem and removed the battery to inspect the electrolyte and found it was O.K. same time I observed that sometimes the rear brake switch getting jammed if brake applied hardly. It was also corrected after riding two days that problem automatically gone today I checked the battery voltage aging it shows 12.60 V while engine off, 12.8V and 13.5V at 1000 & 3000 RPM respectively, either in head lamp on or off.

My problem is left, but I could not find out the reason, I have only two things to suspect one was rear brake switch and another thing I observed while removing the battery the terminal bolts are loose.