And this is?

So I picked some more pieces off tonight and found this on the backside of the right side z plate.



The wiring appears to be original with + ground. The top wire is negative and the bottom is positive. What is this and what is it for?

Also found this little thing and have no idea what it is. :?: :?:



Thanks for any information.

Zener diode on the Z plate to drain excess charge off the alternator/battery , basically in the form of heat, the second item is your rectifier!!!
Regards Mike

Primitve Lucas rectification device is frail, no mis-handling...the wasted energy [ : heat as B.850 noted] is spent on the Z mount which is large enough to not get too hot.
Other Brits have a dedicated sunburst shaped casting under the headlight.

What camera did you use to take those pics Dirt2Oil ?

Aw its the factory time bomb ticker and detonation device. Just leave it alone and it will do its task soon enough. Can't tell if the Zenor wires are just dirty or showing charring.

Treat these items with care.

The black thing is the rectifier - it takes the alternating current from the alternator and converts it to DC current. One lead goes from the alternator to the bottom plate, the other alternator lead to the top plate, and DC comes out the middle plate. If you look at it, you'll see diodes between the plates which provide a one-way path for the current.

The brass thing is the Zener diode. It is a semi-conductor that is open below around 13.5 Volts. As voltage increases, the resistance in the semi-conductor decreases, shunting excess current to the Z-plate (footrest support bracket) in the form of heat. It is important to have that Z-plate grounded well to the harness for the Zener to work well - those red wires mounted just next to the Zener are for that purpose.

My Zener just went bad after 39 years. Suddenly blew the fuse. Replaced the fuse - blew right away. Unplugged the Capacitor, rectifier, power plug and zener and checked each.

There's a whole procedure to test Zeners in the shop manual, but I use this method:
A good zener will show open circuit with the negative lead on an ohmmeter on the grounding post and positive on the spade, and 5-10K resistance with leads reversed. Mine showed 0 resistance both ways. BTW, a negative ground Zener is just the opposite, and looks identical to a +ground Zener.

Went to my local guy - he was out of new ones, but sells good used parts at 1/2 the price of new. Check through a handful of Zeners and picked the prettiest one. Current price for a new Lucas Zener is about $48, so it cost me about $24.

Hegel said:

What camera did you use to take those pics Dirt2Oil ?

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It's a Nikon D5000.

hobot said:

Can't tell if the Zenor wires are just dirty or showing charring.

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I think it's just the 40 years of tar, gravel, and oil I have been cleaning off for the last two weeks. I will have a closer look at it though to make sure there is no charring.
Thanks for the information everyone, your help is greatly appreciated.

Yes do check as that zenor diode may be only solid state electronic device on a Norton but it heats up dumping excess voltage, which is a Commando oxymorn so likely just grime, but maybe a mystery to solve, as just jumping a car to bike battery ain't enough to cook the zenor unless left on while reving a long time, til bike battery boils off. Maybe there was a short to Earth at one time and catch before insulation fell off.

BillT said:

There's a whole procedure to test Zeners in the shop manual, but I use this method:
A good zener will show open circuit with the negative lead on an ohmmeter on the grounding post and positive on the spade, and 5-10K resistance with leads reversed. Mine showed 0 resistance both ways. BTW, a negative ground Zener is just the opposite, and looks identical to a +ground Zener.

Went to my local guy - he was out of new ones, but sells good used parts at 1/2 the price of new. Check through a handful of Zeners and picked the prettiest one. Current price for a new Lucas Zener is about $48, so it cost me about $24.

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Excellent advice regarding your testing method imo :wink: Interesting regarding 'New Lucas Zeners' as i was under the impression that no genuine ones are produced these days, unless your guy has access to NOS. :?:
All the Zeners is see these days are aftermarket, or knackered old ones!

BA10BOON said:

Interesting regarding 'New Lucas Zeners' as i was under the impression that no genuine ones are produced these days, unless your guy has access to NOS. :?:
All the Zeners is see these days are aftermarket, or knackered old ones!

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He has one negative ground Lucas Zener - he had sold his last positive ground Lucas Zener a couple of months ago. The $48 is the price on the bag that had the negative ground zener, which was the list price when he got it. He had an aftermarket positive ground Zener, for about $22, but it looked pretty frail - a little silver thing about 1/2 the size of the Lucas, with the spade on the end of what looked like 14 gage wire.