Well I'll be ***$$&&***
28/12W for a stop/tail...
There are two of those in the back of my Triumph - my wife still bought me a hi-vis jacket afetr following me down the motorway one drizzley morning. She said that, compared to most of the cars, I was almost invisible in the spray and poor light.
Did you do a straight VI measurement?
I might try that.
On a similar thread, if headlamp bulbs are built to a similar standard, who's to say that I'm not trying to light a 100W lighthouse with my puny 500/4 alternator... (?)
I remember a DOT study that was briefly published in 1971 that stated something like, "...single-point rear illumination is fully insufficient in murky driving conditions...". I've partly remembered it for the obfuscation of the intended parameters of the indication...and, it was replaced with another "opinion" in 1973 that said otherwise...but, it caused Honda and BMW to briefly add 2 rear lights to several models, along with "driving lamps", both of which were the turn signals. The rear ones got red lenses, and all around got the dual-filament bulbs. I think the 550K1 suffered this, too, which led to their "increased alternator output" ad for this model, though I always thought that was some sales gimmick. The only way I could keep my customer's batteries up on those bikes was to change the front turn signals to single-filament sockets and use some RV trailer dual-filament lamps for the rear "running" lights (1 cp low filments) or change those to single-filaments and let them remain turn signals only, again. And, use stock headlights.
Do you know what your headlight bulb is now?
One other thing comes to mind, because of the age of these bikes: clean the contacts where the alternator plug connects to the frame harness, then add a drop of oil or grease to each blade, and cycle them at least 10 times together to clean off the age-old encroaching corrosion. I often see a white powder here that makes a good insulator: sometimes I have increased the measured charging current on old 750s by more than 3 amps by just cleaning this connector's contacts: 500s wouldn't be much different. On my own, after it sat 5 years (following my operation), the battery was low (12.0-12.2 volts) until I performed this ritual: now in hot weather it reaches 13.6 volts in my weekend checkups.
