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Quote
I installed a 7.5 amp fuse en route

in route to what , from where ? between starter relay C4 and ? ... the Boyer white
( with the wire from the kill-switch connected ... at the Boyer white also ) .

C4 should only be hot when the start button activates the starter relay .
the fuse needs to protect against overloading the kill-switch ( in a couple of unexpected scenarios )
( there is a possibility for current to go both ways when the start button is pressed )

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Originally Posted by Randy M
thanks so much but I did check the same connections as in your photos and they looked as new. Also I had the ign sw apart last summer (no use since then other than the aborted test ride) and the terminals all looked fine.

However, as you mentioned previously, operating the ignition switch seems to cause things to change so could be worth another look.



Originally Posted by Randy M
I DO have 13.75 v where the Yellow& White (also Blue and White) wires come back to the seat area from the kill switch after going from batt to ZD to ign sw to kill switch.

If, as you said previously, white/yellow is powering the Boyer as it had been white/blue (there are white/blue WU and blue/white UW wires on a T160) then white/blue shouldn't have voltage so needs investigating where it's getting its power from.


Originally Posted by Randy M
Thanks to you after about 180 hours spent I now have spark during cranking (and kicking, and under compression) by following your and Stuart's advice. I installed a 7.5 amp fuse en route.   However weirdly after I disconnected the batt to solder in after mocking up, when i reconn the batt the dash lights lit up. (Current going in reverse?) Not knowing what to do I turned the ign ON and then OFF and that seemed to reset it and its normal again.

It seems unlikely that power going to the dash lights would have come from the C4 terminal without the starter button being pressed, and once again, operating the ignition switch appeared to cure an apparent problem.


Originally Posted by Randy M
Any thoughts on issues A and C?

I thought 'A' was what we had been discussing.


Originally Posted by quinten
C4 should only be hot when the start button activates the starter relay .
the fuse needs to protect against overloading the kill-switch ( in a couple of unexpected scenarios )
( there is a possibility for current to go both ways when the start button is pressed )

If there's no power in the electrical system then the relay wouldn't operate but if power was lost during the relay operation then I expect that could happen.
A diode (oh no, back to diodes again) connected to WY I think would prevent that.

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Randy M Offline OP
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Q to LAB: I have the Yellow & White wire connecting (under the main frame, above the carburetors) to the Boyer unit white wire AND to the relay terminal C-4. In the new wire between that T junction and the relay I have a 7.5Amp (US rated) fuse. So I should splice in a diode in the Yellow and White wire say just before the T junction e.g. "before" meaning facing the front of the bike not back to the Boyer unit which is sitting behind the battery? And it shld be installed so that the black Cathode faces the front and the red Anode faces back toward the Boyer, so that current cannot go forward to the kill switch?
Incidentally these diodes I got -the thickness of the wires emanating from them is OK , about same as the actual metal wires in gauge 18 wires, but the diode itself is so tiny it is hard to believe they can handle any current without blowing up or melting. Fascinating little buggers. I feel like I am a student in electricity 101. Thanks for being the teacher.

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Originally Posted by Randy M
I have the Yellow & White wire connecting (under the main frame, above the carburetors) to the Boyer unit white wire AND to the relay terminal C-4. In the new wire between that T junction and the relay I have a 7.5Amp (US rated) fuse. So I should splice in a diode in the Yellow and White wire say just before the T junction e.g. "before" meaning facing the front of the bike not back to the Boyer unit which is sitting behind the battery?

Yes.


Originally Posted by Randy M
And it shld be installed so that the black Cathode faces the front and the red Anode faces back toward the Boyer, so that current cannot go forward to the kill switch?

Yes.

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Hi Randy,

Originally Posted by Randy M
I have the Yellow & White wire connecting (under the main frame, above the carburetors) to the Boyer unit white wire AND to the relay terminal C-4.
This is wrong. The White wire into the Boyer-Bransden "Transistor Box" should be connected only to the White/Yellow wire from the handlebar kill switch.

Starter relay C4 is (should be) only 'live' when the starter button on the handlebar is pressed, this is (should be) the only thing that operates the relay. I'm assuming you aren't intending to ride with the starter button pressed constantly? If so, connecting relay C4 to the B-B Transistor Box White wire does not serve any useful purpose.

From http://www.boyerbransden.com/pdf/KIT00054__BOX00021_.pdf:-

Quote
General Data:
7) The T160 machine has ... a ballast resistor fitted in the circuit.
This must be removed and the white ignition box wire connected to the live wire feeding it with the ignition on.
... the "live wire feeding it [the ballast resistor] with the ignition on" is the White/Yellow wire from the handlebar kill switch.

Originally Posted by Randy M
In the new wire between that T junction and the relay I have a 7.5Amp (US rated) fuse.
The wire from relay terminal C4 was/is [b]only[/b] to bypass the ballast resistor when the electric starter is in use.

As the ballast resistor is removed when any electronic ignition is fitted, relay terminal C4 and any wire from it to the ignition become redundant.

Therefore, there should not be any "T junction" - the White wire into the B-B Transistor Box should simply and only make an end-on junction with the White/Yellow wire from the handlebar kill switch.

A 7.5A fuse only for the electronic ignition can be fittd anywhere between the kill switch and - in your case - the B-B Transistor Box; a convenient place to fit the fuse is in the end-on junction between the Transistor Box White wire and the kill switch White/Yellow wire.

Originally Posted by Randy M
diodes
Fascinating little buggers.
Is your T160 a bike to ride or just an exercise in seeing how complicated you can make the electrics?

Originally Posted by Randy M
I should splice in a diode in the Yellow and White wire
A diode between the kill switch and the B-B Transistor Box cannot and does not serve any useful purpose on a bike to ride.

Hth.

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Originally Posted by Stuart
Originally Posted by Randy M
I have the Yellow & White wire connecting (under the main frame, above the carburetors) to the Boyer unit white wire AND to the relay terminal C-4.
This is wrong. The White wire into the Boyer-Bransden "Transistor Box" should be connected only to the White/Yellow wire from the handlebar kill switch.

Starter relay C4 is (should be) only 'live' when the starter button on the handlebar is pressed, this is (should be) the only thing that operates the relay.


There's been no suggestion (or need) to "operate the relay" another way.


Originally Posted by Stuart
I'm assuming you aren't intending to ride with the starter button pressed constantly?


Randy shouldn't have to. When the starter button is released the Boyer box should continue to be fed by white/yellow from the kill switch same as would happen for the original points (and ballast bypass) system.


Originally Posted by Stuart
If so, connecting relay C4 to the B-B Transistor Box White wire does not serve any useful purpose.


It can, and apparently does as the Boyer will get direct battery voltage from C4 whilst the starter motor is in operation (and which Randy has said, works) just as if it was powered from a relay* so the Boyer box isn't reliant on the available volts from the ignition circuit, but I agree it's not an ideal situation as it is compensating for an excessive voltage drop in the ignition circuit during starter motor operation.

*(An alternative would be to power the ignition from a relay then the C4 connection wouldn't be required).



Originally Posted by Stuart
Originally Posted by Randy M
In the new wire between that T junction and the relay I have a 7.5Amp (US rated) fuse.
The wire from relay terminal C4 was/is [b]only[/b] to bypass the ballast resistor when the electric starter is in use.

As the ballast resistor is removed when any electronic ignition is fitted, relay terminal C4 and any wire from it to the ignition become redundant.


Therefore, there should not be any "T junction" - the White wire into the B-B Transistor Box should simply and only make an end-on junction with the White/Yellow wire from the handlebar kill switch.

Under normal circumstances I'd agree, however, connecting C4 to Boyer white as an auxiliary feed with apparently less voltage drop seems to be the only way Randy can get sparks during starter motor operation.


Originally Posted by Stuart
A 7.5A fuse only for the electronic ignition can be fittd anywhere between the kill switch and - in your case - the B-B Transistor Box; a convenient place to fit the fuse is in the end-on junction between the Transistor Box White wire and the kill switch White/Yellow wire.

That's not the intention. As quinten mentioned previously, the fuse preferably needs to go in the C4 wire.:

Originally Posted by quinten
"relay terminal at C1 is an unfused battery connection .
when the starter relay is energized ... C2 an C4 are contacted and have
a fairly Direct battery connect .
... if it solves the problem ... fuse between C4 and Boyer box white"


"C4 should only be hot when the start button activates the starter relay .
the fuse needs to protect against overloading the kill-switch ( in a couple of unexpected scenarios )
( there is a possibility for current to go both ways when the start button is pressed )"



Originally Posted by Stuart
Originally Posted by Randy M
diodes
Fascinating little buggers.
Is your T160 a bike to ride or just an exercise in seeing how complicated you can make the electrics?

However, it seems the only way this Boyer will spark during starter motor operation.

Originally Posted by Stuart
Originally Posted by Randy M
I should splice in a diode in the Yellow and White wire
A diode between the kill switch and the B-B Transistor Box cannot and does not serve any useful purpose on a bike to ride.

As quinten mentioned, if C4 is added" "there is a possibility for current to go both ways when the start button is pressed" and a diode in WY should prevent that possibility.

Last edited by L.A.B.; 10/31/20 8:08 pm.
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try to keep up Stewart ... read the whole thread .
no one needs rescuing .

the right way to do would be to clean up the wiring from key switch , to kill ... to Boyer box
... so that there isnt excessive voltage drop , even when the starter load is added .
the wiring is old with previous owner modifications .

pulling the gas tank to expose the harness... opening the headlight ... pulling apart the handlebar cluster switch
is not a walk in the park
the OP did not choose to pursue this path ... when a wiring alternative presented itself
that is ultimately more convenient .

jumping extra power when the C4 terminal is live ... is a creative alternative ... i think the credit goes to lab .
but this seemingly simple fix ... created some new problems .

C4 is and unfused battery connect ... so i recomended a fuse be added . .. it protects the kill switch
more than the Boyer . .. the Boyer protects itself if it's wired correctly .

the diode prevents power from going backwards into kill and back into the harness ... there appeared to be some unexpected idiot lights
being back fed ... at one point ...
how much power can the kill switch hande ? ... are the old contacts sticking ?
but the diode will also drop 0.7 Volts ... all the time the Boyer is powered from the kill ... I'd probably leave out the diode ,
and let the fuse limit what can pass back into the harness ... if the fuse blows all that is lost is
the extra Parallel Power feed ... when C4 is hot ... and the fix is disabled , back to square one .

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Originally Posted by quinten
jumping extra power when the C4 terminal is live ... is a creative alternative ... i think the credit goes to lab .

I'm sure it was mentioned on the TOL forum some time ago so I can't take credit for it.

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Hi everyone, Randy here. I seemed to have stirred up quite a lively discussion. To add to this hornet's nest: A friend who is a biker (Matchless, Norton) and has a Masters of Engineering (more on metallurgy than electronics but he seems to know a lot about electricity) thinks the reason the idiot lights came on was more likely a failing ignition switch, and no need for a diode between the kill switch and the B-B "box". The ign switch on his 1974 Commando recently failed and the bike has only 1800 miles on it (he bought it new) and has barely been ridden in last 25 years. Lucas "quality" I suppose. He also thinks that since the zenor diode is a diode adding another one is redundant, although he has not seen a wiring diagram. (The ZD is NOT where L.A.B. suggested it be located.) .
When I get back to the bike in the Spring I will see how often this happens and if more than when I first hook up the battery will try the diode remedy and if that fails then a new ign swtch. Just to be clear the lights did not go on when starter button pushed, just when I hooked up the battery (key in OFF position) after removing it to install and test the fused wire going from C-4 to the White & Yellow from kill switch which I had soldered to the white B-B input wire.
Also lots of talk about the wiring being messed up on my bike but it does have good original wiring per the stock wiring diagram except for what the Previous Owner did to install the Boyer (correctly from what i can tell from the B-B instruction sheet and diagrams provided in this thread; and it DID run OK for about 6 years, other than a) vibration and b) the U.S. made 867 kit it came with had very thin barrels and I got a big hole in one piston, the same cylinder that still likes to self-ignite in the muffler after ign is switched off, and c) the PWK carbs I installed would not idle under 2500 rpm in summer heat, same carb issue on a friend's Norton) A few years ago I replaced but did not alter the scheme of some rear turn signal wires, replaced the flasher unit and some sloppy headlamp bulb plug connection, and I know a previous expert mechanic replaced the solenoid and the partly snapped off red plastic kill tab but presumably did not change anything else inside the switch and would have if he has noticed it needed it. There is 13.7 volts where the White & Yellow wire connects to the white wire that goes to the B-B "box" so I do not think there is any significant "drain" from bad wires, switches or connections to search for.

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Originally Posted by Randy M
To add to this hornet's nest: A friend who is a biker (Matchless, Norton) and has a Masters of Engineering (more on metallurgy than electronics but he seems to know a lot about electricity) thinks the reason the idiot lights came on was more likely a failing ignition switch, and no need for a diode between the kill switch and the B-B "box".

As several of us have repeatedly suggested, there is a fault somewhere in the ignition feed and which could be inside the ignition switch.

If you find the fault and fix it then there should be no need for a diode or the extra C4 wire to get sparks during starter motor operation.



Originally Posted by Randy M
The ign switch on his 1974 Commando recently failed and the bike has only 1800 miles on it (he bought it new) and has barely been ridden in last 25 years. Lucas "quality" I suppose. He also thinks that since the zenor diode is a diode adding another one is redundant, although he has not seen a wiring diagram.

I haven't suggested you fit a "Zener" diode and neither has anyone else.


Originally Posted by Randy M
(The ZD is NOT where L.A.B. suggested it be located.).

I haven't suggested locating a Zener diode anywhere, only a diode.

The standard Zener diode would normally be attached to the finned heatsink below the headlamp and is the voltage regulator part of the charging system, not part the ignition system although a faulty Zener could possibly cause a voltage 'drain', but your voltage readings seem to disprove that.

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I have original Lucas switches that are still working but I do not have them sitting around unused for 25 years. Possibly it became corroded from non-use? They are not exactly sealed switches.
13.7 volts is when the engine is running? You do not get voltage that high with a lead-acid battery without the generator putting out. Using a LiFePO4?

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