I'm not sure why the MC manufacturers suddenly all went -ve earth although I did hear that car manufacturers found that +ve earth was causing the cars to rust quicker through some electo-chemical reaction, maybe MC's did it just to ensure that the electrical parts suppliers could produce similar parts at no extra cost. Nowadays however some additional parts and upgrades may not work unless you have a -ve earth system, although most will if you isolate them and run seperate supply and return wires. I tend to change my bikes over to -e if I fully rewire as I find it easier to think that way, having been bought up on modern cars and japanese bikes.
I agree with a lot of what SBoyd and RF Whatley say, although I feel that little of what's been said misses the point of my article. Firstly I also hate the positioning of your unit, mine are usually fitted on the rear mudguard or onder the battery tray out of sight. There may also be variations on these units... the two I currently have available for testing have earthed heatsinks and therefore I recommend isolation on +ve earth installations, althought they might not ALL be like that I prefer to recommend safety. SBoyd beat me to it on recommending finding out how your system is wired and he was spot on. As for size, there are smaller units available but how much current can they handle and are they 3 phase.... my article was aimed at 3 phase installations only and I run my units on 180-240w capable systems, although I hope I never draw anything like that! :-) Your installation sounds like a bodge and I would recommend paying the 50UKP equiv. and getting a 3 phase stator as this is all you'd need to change to make things work properly other than taking RF's advise and moving the cylinder head wire to a better more common ground. I would not leave the 2 phase alternator trying to run the 3 phase RR... one has to go, and the advantage lies with changing the alternator rather than the RR in my opinion.
I think this covers everything, but I can be contacted off the forum at email@example.com should you have further questions.
Thanx Chris....the unit has been removed already...and yes i was tossing up whether to replace it or go 3 phase and the money would be better spent improving the output....ive already started on the wiring etc and ill be mounting the rectifier on the mudguard under the battery tray...i guess the PO didnt want to pull half the bike apart to get at this area..... can the stator just be changed and use the same rotor? thanks again for the great answers....i knew very little about the bike electrics beforehand....
"What are you rebelling against? What have you got?"