I was out on my R80 this evening and the dipped beam blew, I was about 1/2 mile away from home so I switched to the main beam and the cars would have to live with it. It lasted about 2 seconds. Literally. I pulled over and found that the side light had also gone (I don’t know when in the sequence it had failed) but the rear lights were OK. I carried on as there was little traffic apart a van that I followed. Ahem, sorry officer. The bulb is a standard power of Osram parentage - they have been in for about 20 miles after the last one failed.

So clearly there is an electrical issue. Other symptoms are that the battery doesn’t seem to be holding its charge too well evidenced by a sluggish turn over when starting.

OK, so my assessment is as follows.
1. The battery needs to be replaced (it is a gel battery and about 3 years old but didn’t get used enough for 2 years as it was off the road) - this change is planned anyway
2. The bulbs blew due to high voltage as I think the voltage regulator may have fried as a result of the battery being half dead so would need to be replaced.

Firstly question - do my assessments make sense and / or are there any other things that I should look at?

Second question - as it is a standard alternator and I am intending to replace it at some point for a 400W Endurolast system do I bite the bullet and replace the alternator now (as well as the battery) or just the voltage regulator (assuming it is fried)? I am not fixated on the Endurolast system but I am not after vast amount of power either as I am not planning on running anything with that draws much power but could do with a little more than the standard 280W (having said that is the 600W on sale at Motorworks worth looking at?).

For the record the bike is an R80 Mono from 1986.

Thanks for any advice.

Yes, all you have said could result in a good repair.

On the other hand it may not. The diode board could have a shorted diode. I'd test it.

Once you have replaced things ... check the charging voltage of the system.

And get ready to replace a few more globes - they too will have been stressed by a higher voltage leading to a shorter life. I'd replace the tail/stop light just as a safety matter, most of the other lights will tell you when they fail.

----------------------
You do know that you need to disconnect the battery to remove the front engine cover? Not doing so can blow the rectifier.
--------------------
Why the replacement of the alternator? Unless your running hi power accessory electricals more power is not needed.

Thanks for that - I will first visually inspect the board to see if there is anything obvious then test the board and check the charging voltage.

Changing the rear bulbs makes sense. I should have thought of that myself.

I knew that I had to disconnect the battery when removing the front engine case - I cant remember where I picked it up from though, quite possibly this good place.

I am gradually fettling the bike ready for a trip in a few years and I will want to charge various items so having some head room on the charging side makes sense to me.

The problem with going 'non standard' is it reduces the chance of finding replacements if you breakdown. The voltage regulator was fitted to many older vehicles ... including trucks and tractors... and old motoguzzies. Should be able to get one at any auto-electrician, or any automotive spare parts place.

I know that but the Endurolast has a good reputation for reliability. Also I won’t be against the clock (maybe against a monthly calendar but not much more) on my trip so I can wait for spares to be shipped out to me - I wasn’t planning on getting rid of the original but leaving it at home. What that would mean is that I would have to get the shed organised for other people, I can find things but no-one else could be expected to easily.

On the plus side it would mean that I would get a chance to explore a specific area better.

Well I have started the testing process but got driven in by the cold - it is about 2C here and as I don’t “need” to get the bike ready in a hurry I retired inside.

I am pretty convinced that a voltage cross the battery of 16V when I rev the engine up to 3,000 rpm is not normal. So the voltage regulator is fried. I suspect that whilst stripping things off to get that changed I might as well replace the diode board as well.

And then comes the crunch decision - the cost of replacing the diode board and the voltage regulator is £112 but the cost of the 400W Enduralast complete kit is £270 though Snowbum seems to like the 600W Emerald Isle system more (I think that is about £420)...... decision, decisions.