I had this problem a few weeks ago, thought it was maybe a bad earth, a short etc. But the problem went away when I started having battery and charging issues. But now it's back again...

Last night I removed my five home-made connectors from the generator. I rejoined the wires with soldered-on bullet connectors. I also bit the bullet (arf arf) and installed my new Shorai lithium iron battery. On my ride in to work, voltages were better than before, about 13V with headlamps on and over 13V with headlamps off (at 3-4,000 rpm). After sitting for 3 hours the battery now reads 13.2V at rest. So I'm hopeful...

But as I said, now that I seem to be getting a better charge and have a new battery, the fuse has blown again.

Any ideas?

Thanks.

 

I don't like electickery at the best of times.

I think the temptation is to link these two problems, but the best thing is to keep an open mind.

It would appear (fingers crossed), that the charging issue is resolved, so if you haven't already, trace the wiring and inspect every connector in the circuit, if that turns up nothing, inspect every inch of wire in the circuit. It could still just be a worn section of insulation shorting things out.

The wiring looms on these old girls are getting old now, vibration will do it's evil deed over time.

 

I have to agree with Hawk - I'd start at the rear wiring loom - lots of vibration back there and it's probably either a loose earth or a live wire that needs new insulation.
At worst it'll be time consuming but a cheap fix
I don't think the two problems are linked. Just coincidence.
Is it both brake and tail light ? - I don't know if you have separate fuses on your bike.
Maybe just an old bulb ?
Good luck with it.

 

They may be -->IF<-- and I do mean if, there is a short that is draining the battery. I suppose the short would not be fused.

I'd start by checking the wires and then the light assembly.
I'd check the light assembly by unplugging it and removing the bulbs. Next check for continuity from the hot side wire of the assembly to ground, there shouldn't be any unless you have a short.

I have seen in a couple of cases where in a double element bulb, one element craps out and drops and shorts across the other element. Carefully check the bulbs by holding them up and flicking a finger on the bulb to see if you see any movement in the elements.

 

Thanks Shadow and Timbuctoo.

The bulbs work in 'park' mode and the brake lights work too. Instrument panel lamps are dead but I guess that's how the bike warns you that you've no rear light!

Noticed today that the front 'park' bulb has blown too, don't think it did that previously.

I'll check the bulbs and the wiring as you've suggested.

Currently have a couple of bicycle LEDs strapped under the rear light above the license plate. Brighter than the original light in fact.

 

fom experience of some old cars(pre-computerised) i'v seen an alternator start overcharging and blowing bulbs, always at the furthest point. would be worth checking it just for the sake of a meter on the battery at 5-6k.
son's bike started flashing the dash lights when riding it fast, and it was led dash, and after 4-5 stop light bulbs in it , i replaced the rectifier and it never done it again.

might be nothing to do with yours. but it's a 2 min check.

 

Thanks Ken. I've been checking the voltages a lot recently. After a jump start from a taxi and a rapid charge from the RAC my new (£128) LiFe battery displayed a fault on the (£64) charger but thankfully a few charge cycles seem to have restored it. The RR doesn't seem to put out more than about 14.5V at 4,000rpm, so I hope that's OK. It's the fuse for the rear light and instrument panel that blows, but the other day the little front parking bulb blew too.

 

Given the age of the bike, it's possible the front park bulb was just old. Our bikes are all around 25 years old, and I'm still running my original indicator bulbs from 1990 !
14.5V at 4000 is fine.
OMG if I had to pay the equivalent of 128 pounds for a battery I'd faint !!
Batteries here (Yuasa) are around 45 pounds, and I use a locally made one at 28 pounds ! Good for around 3 - 4 years. Maybe I should start an export business !! LoL. a good battery charger here would be about 10 quid..........
Regularly checking the water levels in your battery is a must (unless you have a gel battery)
Low water levels are the cause of most reg/rec failures....
BTW I went through a stage of blowing rear bulbs too - turned out to be cheap/old bulbs.
Bulbs get affected by humidity which is a real killer here.

 

Thanks Shadow.
My previous battery was a Motobatt, which is a sealed AGM battery - about £60. The new one is Lithium Iron - £128. A quarter of the weight of a standard battery and doesn't lose charge when stored, even in the cold. In fact they recommend to store it in a fridge!

 

Let's hope at twice the price it lasts twice as long.................