Britbike forum Forums British Motorcycle specific Brands Norton bulletin board 1970 Commando front brake switch power

New harness and Pazon installed.
Replaced the 12V coils with 6V PVL's in series.
Got it back together enough to kick it and to my surprise it started right up.
I ran right out and bought a lottery ticket.

In doing a quick function check, rear brake, light; front brake, no light.
Wiring diagram shows a single white wire feed to brake switches from ignition switch.
Apparently the front brake switch had been fed from the same white as the 12V coils.
That white now powers the Pazon.

Is it bad form to tap off the Pazon power feed, or better to run a loose wire back to the ignition?

Cheers

I wouldn't try to power the front brake switch from the Pazon or other EI power supply, the risk is that when the brake is applied the voltage drop may affect the EI system.

Your best bet as suggested would be to run a wire from the ignition switch directly to the handlebar lever and create an independent circuit to the brake switch.

Thanks gunner.
This is where my weak understanding of current/voltage/resistance interplay is exposed.

Both the white wires are ganged on to a single terminal at the ignition.
One apparently fed the rear brake switch, the other fed the original coils with a jump out to the front brake switch.
A voltage drop on one of the wires (closing the rear brake switch) would not affect the other in that configuration?

this does not create an independent circuit .
If the brake light is faulty , like to ground , it will still draw down the power
from everything attached through the ignition switch .

the original Commando wiring plan worked on thousands of bikes for decades and decades years .
It's mostly very similar to the Triumph and bSA plans .

Basically any key switched wire that in the harness under the seat feeds the rear switch
and any switched white wire up front can feed the front brake switch .

you would have to feed both front and back switches from
a current limiting fuse to potentially separated it from the voltage seen at the Pazon .

( on further review , the front brake light switch should be moved to any other
white wire upfront in the harness ... because right now the front brake power runs through the kill switch .
not a big thing , but you loose the front brake light when the engine is killed )

The white wire that powered the original ignition system should now be powering the Pazon. The white that powers the brake light circuit should also be connected to terminal 2 of the master switch.

https://granttiller.com/wp-content/uploads/2020/03/Pre-1971-Commando-Pazon-Sure-Fire.png

It does.
It is.
But is there any electrical difference in teeing off the Pazon feed as opposed to running wire back to the terminal?

https://granttiller.com/wp-content/uploads/2020/03/Pre-1971-Commando-Pazon-Sure-Fire.png[/quote]
Thanks for this.

Possibly not an ideal solution as others have mentioned.
I would have thought modern replacement harnesses would have both brake light switches connected to the same master switch terminal 2 white as shown on the Grant Tiller diagram but if not, then there should already be another white (somewhere?) that goes to the front brake light switch? If so, then it would be better to connect that wire to the existing brake switch white or master switch terminal 2.

There is an open white that runs to the front brake switch.
But it was powered from the white that went from terminal 2 to the original 12V coils.


Thanks all for the pointers.
I'll run a separate wire back to terminal 2.

Although perhaps not the best option as previously mentioned, you could try connecting the front brake switch white to the Pazon power white as long as it doesn't result in the ignition misfiring or cutting out when the front brake (thus switch) is used.

Thanks L.A.B..

I'm probably sounding obtuse about it.
It's the common terminal aspect that seems odd to me.
In my understanding if there is a problem with any part of that circuit, e.g. the rear brake switch shorts, then the Pazon would be affected as it has a common connection.
So running a separate wire back to the same terminal still involves both the brake switches and the Pazon feed in the same circuit.
?

No, the Pazon shouldn't be affected as the current from a potential brake switch short will travel along the brake switch wire (until the main fuse hopefully, blows) from the point where it connects to the Pazon power wire.


No, as all the white wires are basically 'common' at one point in the system (the master switch terminal 2).

I purchased a front brake cable that doesn't have the switch in it. Its a bad set up to begin with and it gives you a vague feeling at the lever.

I know what you mean.
I purchased a new switch from CBS and the take-up range is pretty tight. I also crank the adjuster down so the switch is slightly pre-loaded.
I like having bright lights.

Hi 'Hugh",
Doesn't make any difference.

'Fraid not correct. If the Voltage drops when the brake is applied, you have big electrical problems. Standard(?) US brake filament is 23W, which is a gnat's under 2 Amps @ 12V. If the battery cannot supply 2A even if you're sitting for a few minutes at a stoplight with the brake on, you have more to worry about than where the front brake switch is supplied from.

As standard, all White wires are 'hot' when the ignition switch is on, so all White wires have exactly the same Voltage between them and battery positive.

What he said.

Makes not a blind bit of difference electrically. "others" are wrong.

Your understanding is basically correct. If Pazon and brake switch are supplied by White wires, whether separate or joined, if the White wire/s is/are both connected to master switch terminal #2, a problem anywhere in the brake lamp circuit drawing more than the standard ~2A will affect the Pazon ... and any other component connected to master switch terminal #2 ...

In reality, assuming standard single fuse, the brake switch short-circuiting will blow the fuse within a few milliseconds of the short occurring. Then the bike will be completely dead electrically.

If the second line is true, the first line is wrong.

As "Hugh" has not mentioned anything about changing "earth" ("ground"), standard '70 Commando is "positive". As such, the current to "a potential brake switch short" will travel from the battery negative terminal, same as it does to the Pazon. Which is why the Pazon (and every other electrical component) will be affected by a brake switch short.

I have one on my T150, a heavier and faster bike than a Commando. Insofar as an 8" TLS drum brake on a 450-lb., 120mph-capable motorcycle is a good idea, it's a very good brake, not in the least bit "bad" ime. Albeit two-up down mountain roads, I'll take twin front discs if it's all the same to you.

Would you like to see how the switch-in-the-cable works? Then you can check where yours are "bad"?

Hth.

Regards,

I think I misunderstood what HJ meant by "affected".

If there was a brake light switch "short" which I assumed to mean a short to 'ground' (and not across the switch?) then the main fuse should blow which obviously would stop the Pazon working but I had the impression he meant affected as being possible damage to the Pazon box.



Yes, I'm well aware of that.



Again, what I thought he meant was the Pazon box being damaged from a short in the brake circuit.

Brake switch short? Does anything more than the brake light stays on ALL the time...

Never heard of a shorting switch (to ground) happening, though that dirty contacts that fail to complete the brake light circuit is more likely.

Thanks "Stuart".

Hi Hugh,
The answer to a question you didn't ask - whether to include a second fuse to offer better protection to the Pazon - might better-inform your decision whether to supply the brake switch direct from the master switch, from the White wire connection to the Pazon or from another White wire connection.

Standard single fuse to 'protect' the whole harness is US 15A. This is pretty useless just for the Pazon if, say, one of the coils suddenly went low-resistance. For this reason, I include a 5A or 7.5A fuse specifically in the supply to any electronic ignition. Ideally, it should be a specific electronics protection-type fuse but, while these are available, I've yet to find a suitable fuse holder. Pending that, I use standard automotive blade fuses/holders similar to this (with a cover).

White wire from the master switch connected to one fuse-holder terminal, Pazon White wire connected to the other terminal, brake switch supplied either direct from the master switch or from another White wire connection would be two ways.

Or third way could be: ends of the White wire from the master switch and White wire to the brake switch connected to one fuse holder terminal, end of the Pazon White wire connected to the other fuse holder terminal.

All the same electrically.

Hth.

Regards,

I'm not sure I fully agree with this assertion, and what's not been mentioned is the thickness of wire in use and the condition of any connectors.

Its fairly common to see corroded connections and often the wire used, particularly on the rear brake circuit can have high resistance especially with corroded connectors.

Consequently I can foresee a situation whereby the Pazon is happily being supplied with 12.6v, but when the front brake is applied, the voltage may drop because of the resistances in the circuit.

I guess much would depend on where the front brake power is tapped off and the condition of any wiring, connectors and earths.

My understanding is that Pazons are OK down to around 10v or so, but regardless of that I would still run an independent brake circuit as shown in the diagram posted earlier. Additionally check for any voltage drop between switches & terminals.

good point .

the white wire in a normal harness is rated to 20 amps ,and fused at 20 amps ( 17.5amps in old money )
and comiing through the ign. switch , which may have its own current limitations . (15 amps )

the Pazon load is Max. rated to 5 amps , but it's normal running draw is about 2 amps
A brake light filament is typically 27 Watts , roughly another 2 amps

the combined load is 4amps from wire with 15~20 amp capacity .
.. the wire is running at 20 to 27% of capacity ... ( no problems yet )

any connections , splices , crimps , or tees "could add resistance ".. .
so it would be slightly better to run a dedicated wire straight from ignition switch to Pazon box ( what no kill ? ).
because no extra connections ... eliminates the possibility that they could go higher resistance .

but this does not Safeguard or isolate the voltage Supply to the Pazon .
there is still only one circuit voltage ... supplying all loads ... and reacting to all loads .
So even if the brake circuit is wired directly to the battery ... with extra tees and splices
and causes an electrical short .
the voltage to the Pazon will still drop .

1.the advice boils down to ... dont added extra spices and tees "anywhere on the bike ."
because they are a potential resistance
2. And the second bit of advice is ... there are practical limits to following advice 1 .
adding a "home run" to each load would make for a bulky harness .






.

"...dont added extra spices"

Yes, give me the blandest wiring available please.

yes no spices !

You know , you can go back and forth on whether to wire the front switch to
the Pazon feed ... if done with good "spices" , it won't cause a voltage drop ..
and the operation of the front switch , each time it's used , is a load test Diagnostic
that the Pazon has at least 27 watts to spare . ( roughly double its average need )
If the brake switch circuit load causes problems , it's an early warning .
or if it works well with the ignition on , so should the Pazon .
( got brake light ? then you should have Pazon too )

If no spices splices at added from the ign. switch to Pazon
... this wire is easier to troubleshoot in the event of a problem
( the problem can never be the splice thats not there )

The white and other standard wires in the harness will be 14/0.30, 1.0mm², 8.75A - cable OD 2.6mm (approximately equivalent to British 14/32 SWG of the original harness or US 18 gauge).

http://www.britishwiring.com/product-p/c114.htm


No kill switch before '1971'.

Quinten, Quinten ...

You've been posting about electrics on this Forum for years and years ... Sometimes I believe you've finally begun to grasp some of the basics, then you burst my bubble posting things like:-

Cobblers ... the original single fuse might be 17.5A continuous but there isn't any way on God's green earth any of the wires are rated for that ... Have you really never, ever bothered to look up Lucas wire current ratings or their modern equivalents?

Original 1970 Commando coils and brake switch/lamp wires were 14 strands, Lucas rated for 7.5A

Afaik, the closest to 17.5A rating you might find on non-electric-start Commandos are 28-strand wires to the battery terminals? Originally rated by Lucas for 15A ...

Please do feel free actually to demonstrate 15A though the standard Lucas ignition switch ...

Regards,

Hi Gunner,

Regrettably you misunderstand certain electrical basics:-

The thread is entitled, "1970 Commando" and Hugh started his first post with:-

... original 1970 Commando coils and front brake switch wires were 14-strand rated by Lucas for 7.5A; unless Hugh was diddled, his new harness has equivalent metric 14-strand rated for 8.75A.

As I've posted already, standard US incandescent brake filament draws under 2A.

As Hugh hasn't posted any different, I've assumed his "Pazon" is a Sure-Fire, the coils cannot draw more than 4A, probably draw less.

So that is a maximum of less than 6A, almost certainly travelling down wires rated for 8.75A ...

... even if "corroded connections" were present, they would be A Fault, just like e.g. a bolt missing from a silencer or a loose wheel. Do you normally ride your bike with loose and missing parts? If not, why would you assume others ride theirs with corroded electrical connections? Moreover, same as no bike maker designs/ed their products to be ridden with loose or missing parts, Lucas didn't design electrics to have "corroded connections".


As has been posted earlier, "the diagram posted earlier" does not show "an independent brake circuit (brake lamp supply)" ...

Hth.

Regards,