Britbike forum Forums British Motorcycle specific Brands Norton bulletin board Plug For Accessory Socket On 75 Mk3

Does anyone know a source for the plug for the accessory socket on a 1975 Commando 850 Mk3? I know there are complete packages of plug and receptacles for sale, but all I need is a plug. This would be very convenient to use with a battery minder.

https://www.rgmnorton.co.uk/buy/commando-power-take-off-accessory-plug_3923.htm

Not much cheaper than the plug and socket.

I found a complete NOS plug and socket on Ebay for a total of $26.15. I intend to use the plug to maintain the battery with a NOCO charger when needed.

How do you go charging the battery with original electrics on the bike ?
Wouldn't the zener diodes be doing battle with the battery charger ??

I've always disconnected one terminal of the battery on about everything I've owned to do any charging.

That smoke is expensive to replace ...

This is correct. though the 14.3 voltage level is slighty higher on a MKIII when your charger will start cooking the twin zeners.

You can find these connectors easier by looking for Land Rover parts, they were fitted to Land Rovers before Commando's.

Gary,
You can get new plugs and sockets of this kind from Walridge Motors in Canada (www.walridge.com). Part number i s 06-2666., and their current price is around $22.95Cdn
.. Gregg

If you want an accessory plug than great, however if your charger like mine goes to 14.8 sometimes, than it will never go to "hold mode" because the zener does not go higher in impedance like a battery would.

The two Mk3 Zeners are connected to the AC side of the charging circuit. With my battery charger connected, the meter reads 15+ across the battery, 0 volts/amps at the Zeners, both of which are stone-cold after many minutes.

So the Mk 3 is quite different to all previous Commandos in that respect. ?

https://granttiller.com/wp-content/uploads/2019/07/1975-MK3-Commando-Original.png
https://i0.wp.com/granttiller.com/wp-content/uploads/2019/07/1972-onwards-Commando-Original.png

I'm not familiar with Norton Commandos prior to the Mk3. The Riders manual for the Mk3 specifically states that you can use the power point to hook up a battery charger or maintainer without having to disconnect anything. This is a very handy feature. The plug is also polarized so you can't plug it in backwards.

yes , or...
its the fitting of the then newer/larger 14amp stator that makes 2 zeners necessary .
And they don't have to be matched if fitted on the ac side
Because they are each only dealing with the peaks of different ac half phases .
During the normal process of rectification .
Pretty ingenious as far as regulating and rectifying with minimal circuitry .


https://www.accessnorton.com/attachments/Commando-mk3-charging-circuit-jpg.77361/


image snagged from l.a.b. at
https://www.accessnorton.com/NortonCommando/wiring-a-solid-state-rectifier.31517/

Yes the MKIII is a bit different.

Les may need to have his meter calibrated as +15 is over the top as what is normaly expected at the battery but not above the zeners ability to dump excess power (the main issue)
+15 V at the battery requires 15.6V to the accessory port!, battery charger on nitrous? My Sears DieHard and Deltran battery tender I don't think don't go that high...but do just keep cooking away.....and eventually go to storage mode.

I would still prefer (and do) pull the fuse and hook direct.on the battery.

" 0 volts/amps at the Zeners" ?

In the final result your bike will probably still start on a slightly less charged battery and.... not kill your charger.

Better charge if direct on battery? I think so !

That was with my battery charger on the 'High charge' setting and eventually dropped back to 0 Amps.
My point is there were 0 Volts at the Zeners.

I just discovered that my NOCO smart charger will not charge the battery in my Mk3 through the accessory port. However, when I hook up a 30 year-old charger to the accessory port, it charges the battery fine. When I remove the fuse, the NOCO smart charger will charge the battery. With the fuse installed and the NOCO smart charger hooked up to the accessory port I measured the voltage at the accessory port. The voltage cycles between 12.3 - 12.7 every second or so for about 15 - 20 minutes when the charger shuts down. I repeated the test with a second NOCO smart charger and again with an Odyssey- brand smart charger with exactly the same results. Something is obviously happening with the zener diodes that is impacting smart chargers. When I measure the voltage at the accessory port without any charger hooked up, I measure exactly 12.0 volts. Obviously, all tests with engine off.

Do you have the 5K uF blue cap? Pull the - neg lead off and see what happens when you try again?
Zeners have a instantaneous response but the cap is like a slow filling air tank,,,,,its could be a mismatch of the the " time response" of the charger circuit.

Maybe try with the 2MC (blue can on a spring near the battery) disconnected? Edit: Dave posted as I was typing.

where are the zeners , on the Z brackets ?
should be easy to feel some heat from them ... if the charger is forcing them open

Yes.



...The Zeners can be disconnected as the terminals of both are accessible and see if that changes anything.

seems to me you could put/leave the 2 zeners , on the ac side ,
but behind a full bridge rectifier . ( not the half bridge as originally supplied)

this would add a bocking diode in front of each zener when charger voltage is seen from
the battery side .
.

I finally received my new plug for the accessory receptacle. The receptacle on my Mk3 is wired such that the rear contact is positive and the front contact is negative. The plug I received is wired so that the terminal that goes into the rear contact on the receptacle is the brown lead. The red lead contact goes into the front contact on the receptacle. The plug is polarized so that it can only be inserted one way. The Mk3 electrical system with positive ground uses red insulation on the positive or ground wires as you would expect. On the plug, it is reversed with brown being positive and the red lead negative. The plug is obviously an original Norton part as it is packaged in Norton packaging with the correct Norton part number. Does anyone else have an original Mk3 accessory plug and if so, how is it wired? I will need to remember that with my plug, brown is positive and red is negative. I thought about rewiring the plug, but I think I would destroy the plug if I tried.

Positive is normally the rear terminal on the socket although if it is removed then the wires can be swapped over.



The pins should unscrew (and the wires could have ring terminals) so it should be possible to swap them over as the plug (or socket) doesn't generally come with wires attached.

https://www.accessnorton.com/NortonCommando/accessory-electrical-plug.21390/post-319281

https://www.rgmnorton.co.uk/buy/power-take-off-accessory-plug-socket_4588.htm
https://andover-norton.co.uk/en/shop-details/15933/accessory-plug-and-socket-06-2099-

I appreciate the help. I didn't look at the plug that closely. The pins on mine do unscrew so I can swap the wires around. My plug came with wires. I'll swap the wires so that red is positive before someone hooks up a battery charger with crossed polarity. I' also going to hook up a pigtail that matches my NOCO charger like I have already on my other bikes. The NOS plug and receptacle I bought has obviously been around a while. It has a price of $6.00 USD on the package!

Yes the plug will not fit backwards but current will flow if the accessory on the other end is on when the pins touch the wrong sockets, so plug in correctly first and then turn the charger or accessory on.