Missing fuse?

Hello to all!

I had recently purchased a MKIII Commando and am working on getting it running in time for the bike season here in Wisconsin. When purchased, the bike did not have a battery. After doing a bit of digging on this site and thumbing thru the Chilton manual, i've deduced that [i believe] i am missing a critical component before i can install the battery. I [THINK] there should be an additional line coming off the [rectifier?] with a fuse that leads to the negative terminal on the battery. Can someone of greater Norton knowledge than myself please confirm or deny this? It appears as though the bike retains a relatively stock electrical setup w/ points and positive ground..



i've done a bit of searching on the site in hopes of finding a posted photo that would answer this question, but no luck!

Ah, another cut-off electric start. That is one bit of electrical complication out of the way.

Your electrics have been moved around and extended quite a bit. I'd be a bit concerned about the two zeners being on that small steel plate out of the airflow rather than on a proper heat sink.

You are correct about the standard fuse fitment. Normally there is one very close to the battery fitted in the brown / blue lead which ultimately goes to the rectifier.

As you have no starter wiring, you don't have to worry about the solenoid so an in-line fuse on the (only ?) battery live lead will be OK.

tom2240zap said:

After doing a bit of digging on this site and thumbing thru the Chilton manual, i've deduced that [i believe] i am missing a critical component before i can install the battery. I [THINK] there should be an additional line coming off the [rectifier?] with a fuse that leads to the negative terminal on the battery.

Click to expand...

Thank goodness you posted the photo, otherwise certain things would have passed-by unnoticed!


1. Firstly, as I'm sure you are aware, the wiring has been somewhat "modified"? The two Zeners have been moved from their original locations (one on each Z plate) and fixed to a plate which, as 79x100 has already pointed out, may not act as a particularly effective Zener heatsink?

2. The photo appears to show that the two Zeners have been connected to the DC output side of the rectifier?
This is not how they were originally intended to be connected when used with the 850 MkIII's RM23 180W alternator, as each Zener would then have been connected to one of the stator AC output wires as shown below.




To use two Zeners on the DC side as they are now wired, means they ought to be a matched pair? When Zeners are individually connected to the AC output as they were originally, then they do not have to be a matched pair.

3. The 850 MkIII double Zener system only requires a half-wave rectifier instead of the full-wave rectifier used with the earlier models' 120W RM21 alternators.
The original half wave rectifier would not run at the full output wired like that with the Zeners on the DC side, but I think that's the full wave rectifier in the photo?
Are there any numbers on the rectifier? As the original H/Wave MkIII rectifier is a Lucas 49181 (2DV 406), the earlier F/Wave unit is the Lucas 49072.

Thanks guys, for the assistance!! After a few week hiatus, im anxious to start tackling this wiring dilemma.. ..and yes, after a little more digging, im starting to understand that this is not much 'factory' left from this [VERY] questionable wiring job...

To clarify on a few posted comments, the 'steel' heat synch plate is in fact aluminum. I'm not sure that this matters much thought, as I would like to correct this concern. Can you please divulge a bit on the location of these 'z-plates' mentioned?

Also, LAB, you are correct in the part identification. The bike is currently wired with a F/Wave rectifier unit (#49072). I will need to correct this as well.





In digging more into this wiring project, i'm discovering that there are loose and taped-up wire ends everywhere, each wire strand has at least two or three splices and most of the wiring for the turn signals, ignition tumbler, taillights have been removed and updated in a less that professional manner. :shock: This leads me to believe that the correct way to address this issue is to start over from scratch. I've done a little digging on this site [using the search feature] and most of my questions have already been answered. Thank you again for all the help and i'll stay posted as to project status.

Later!

-Tom

My MKIII wiring was a complete mess. I figured a complete re-wire would be the only remedy for a neat appearance and peace of mind.

tom2240zap said:

Can you please divulge a bit on the location of these 'z-plates' mentioned?

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The large alloy footrest hanger plates are generally referred to as "Z" plates, and if you look at them, you should find that each one has an unused 1/4" hole in it?
Each hole is for mounting a Zener diode, with the body of the Zener on the inside (pre-MkIII models only have a single Zener on the right hand plate, just in case anyone is wondering why they don't have a Zener on the left plate of their pre-MkIII model?)
The right hand MkIII Z plate should have two 1/4" holes, as the other hole is used to mount the rear brake line hydraulic tee junction?

tom2240zap said:

Also, LAB, you are correct in the part identification. The bike is currently wired with a F/Wave rectifier unit (#49072). I will need to correct this as well.

Click to expand...

You could continue to use the full wave rectifier and double Zener setup as it is, maybe with a larger Zener heatsink? The two Zeners could be a matched pair and it should be possible to get them tested to find if they are or not? However I would suggest that you consider fitting a Podtronics (or similar) type of voltage control box in place of the old rectifier and Zeners?