Wiring 1967 BSA Starfire

[oldgoat]

I’ve picked up a junkyard ’67 BSA Starfire 250, engine/frame number C1429. It was an absolute mess – the PO had installed extended forks, V-line handlebars, now-rusted chrome do-dads. I’ve managed to replace all that crap with stock items, and now I want to get her running. The original wiring harness had been modified and was pretty much rotted away. I bought a replacement, but there are some discrepancies between the wiring diagrams in my Haynes manual (“BSA Unit Singles 1958-1972 Owners Workshop Manual”, 1980). Does anybody on the forum have familiarity with the wiring on this beast? I’ve managed to have ridden for 52 years without ever having to do any motorcycle wiring, so I am a real novice. Obviously with the harness taped up the way that it is, I cannot follow individual wires end to end, so I’m working off wire colors and their positioning on the harness.

So, the first question regards the wiring to the ignition switch (IS). The switch has 3 terminals. According to the manual, the connections should be W from the coil, NW from the Zener diode, and NW from the rectifier. But the IS portion of the harness has two push-on clips: one clip has 2 W wires. I assume this is from the negative terminal of the coil (which has a W wire), but why are there two W wires? The other clip has two NW wires. Are these from the Zener diode and the rectifier? If so, why are they wired together? How should they be positioned on the switch – one at each end, leaving the middle terminal open (or covered)?

The rectifier: It has 4 fins. The outermost one (furthest from the frame) is labeled ("Stud +"), so I assume the red wire from the harness (which has an eye terminal) is bolted there. The other three wires from the harness are NW (I assume from the ignition switch), GW and GY (both apparently from the alternator). Which order should these 3 wires be positioned on the fins?

[iansoady]

That sounds like the old selenium rectifier, very few of which still work. It's best to change to a modern solid state item available for a fiver or so. Alternatively a solid state rectifier / regulator available from the likes of Al Osborn who knows his stuff. http://www.aoservices.co.uk/

There will be no regulation as such in the existing system and it originally probably had the 3 wire alternator on which the light switch switched in extra coils when the headlight is on.

[R]

For 1967ish that would be a silicon rectifier type. ?
If you attempt to tighten the nut and overdo it and they twist, they are toast...

Seleniums were early 50s, and BIG square flat things with wires coming out of them.
The ones I have still appear to work, although I haven't put them to use in anything.
They'd be half wave rectification only ?

[oldgoat]

Thanks for the feedback. I'd like to assume for now that the rectifier is OK, and at least get all the wiring right. If at that point it's not working I will go to a solid-state unit --  I will try to find one in the US, where I am located (Wisconsin). Do either of you which wire goes on which "fin"?

[R]

Is this bike +ve earth ?

The manual you have doesn't show the wiring to it ?

I could quote the Commando connections, but I'm not sure they would be the same.
The earth is usually the frame connection, and the power out (to the battery) is the opposite side of the diode 'bridge'.

The other 2 connections usually don't care which of them is attached to the other 2 connections. They'd be GW and GY.

[Rex]

Thanks for the feedback. I'd like to assume for now that the rectifier is OK, and at least get all the wiring right. If at that point it's not working I will go to a solid-state unit --  I will try to find one in the US, where I am located (Wisconsin). Do either of you which wire goes on which "fin"?

Solid state rectifiers are so cheap and widely available that I'd replace the selenium one before doing anything else. They weren't great fifty years ago, let alone now. Radio Spares or Ebay are good sources for a new one.
Not wishing to contradict Mr Soady here, but Osbourne's lack of customer skills is legendary. If anything goes wrong with what you've purchased it's YOUR fault, and couldn't possibly be anything wrong with his products. As with a certain other  electrical guru and parts supplier, I'd avoid like the plague. Again, there's better and cheaper on Ebay.

[R]

Again, 1967ish would have been a silicon rectifier.
With no voltage control whatsoever.
(boiled batteries rule, OK ?)

Selenium rectifiers disappeared with Methuselah.
If you have to ask who was he, thats how long in the tooth selenium types are !

These modern little ones for $4 or $5 would have revolutionised electrics if they'd been around back then.
But no voltage control with them. They generally come with a wiring diagram.
And take a lot of killing ...

[Rex]

This was the type of selenium rectifier fitted in the 1960s, and still used on my 1972 Triumph Bonnie-

https://www.classicbikepartscheshire.com/electrical-c3/ammeters-voltage-regulators-c20/lucas-rectifier-for-classic-motorcycle-p77/s77?cid=GBP&gclid=EAIaIQobChMI1JKxgv2-8QIVrAUGAB3r2g9hEAQYAiABEgKv8PD_BwE

For1967 there was a change to 12V and voltage regulation by Zener diode.

[iansoady]

I've never had a problem with Al but then I'm a Norton owner......

I wouldn't make assumptions about the rectifier - as said the modern ones are so cheap that you eliminate it as an issue. I would go for a simple zener diode controlled circuit although these are getting hard to come by.

[R]

This was the type of selenium rectifier fitted in the 1960s, and still used on my 1972 Triumph Bonnie-

As far as I know, thats a silicon rectifier. ?

Selenium was obsolete in the 1950s. ?
They were BIG square things, wires coming out of them.
And only half wave rectification ...

Al does say stuff sometimes that you wonder if he really knows ...

[Rex]

As far as I know, thats a silicon rectifier. ?

Selenium was obsolete in the 1950s. ?
They were BIG square things, wires coming out of them.
And only half wave rectification ...
Al does say stuff sometimes that you wonder if he really knows ...

I recall an old Bantam had one of those huge flat plate rectifiers bolted behind the battery carrier. That said, I also believe the type pictured in my link are also selenium.
Dear old Al gets a lot of stick for the poor dynamo regulator he continues to sell (VReg2) but he continues to claim that it's a good one even though for most bikes it won't start charging the battery until about 30mph is exceeded. It also has a strange habit of not "switching on" for some reason although when asked about this it's because of "the way you've wired it"
 The newer DVR2 is 100X better.