Turning on headlight kills ignition

[pa-powerstroke]

So i have a 79 xs with boyer ignition, hhb pma, capacitor obviously running no battery. I have the bike wired up and everything works great. Brake lights, ignition, speedo backlight, but occasionally when i turn on my headlight it kills the ignition. Sometimes it works, sometimes it doesnt. I go to kick the bike over again and the lights come on as the motor spins but i get 0 spark. Shut the lights off, kick it, starts fine. Like i said sometimes i can turn the headlight on and it will run fine. Rpm does not affect this at all. Its like my ignition is getting grounded out somehow. I have tried a bates style headlight and a low draw led light so i dont think it is pulling too much voltage. Has anyone had something like this happen before? My wiring diagram is identical to the second picture on this thread:http://www.chopcult.com/forum/showthread.php?t=17549

 

[Eotnak]

High resistance fault, or more likely bad electronics/poorly installed electronics. Note the conditions when the problem occurs. There is no such thing as too much info.

 

[pa-powerstroke]

I wired it up, started it, turned the light on and it was fine. Came back an hour later and it gave me problems. I cant duplicate it and nothing changed between first and second time. Thats what stumps me. Are you thinking its bad wiring to the light since that seems to be the only thing that causes it? Other lights and ignition work fine so i can imagine them as a problem. Maybe i should just rewire the light.

 

[Eotnak]

One should not affect the other, they should be on separate circuits separated by appropriate fuses. If switching the headlight on/off affects ignition, you're wired wrong.

 

[5twins]

Have you checked your charging output? If it's too low, the headlight may be sucking up all the available power, not leaving enough to run the ignition.

 

[Eotnak]

Have you checked your charging output? If it's too low, the headlight may be sucking up all the available power, not leaving enough the run the ignition.

Exactly. Sometimes I'm in such a hurry I forget to be methodical. Start at the source and work your way out.

 

[retiredgentleman]

The Boyer ignition likely wants to have a nice steady voltage, such as 12 to 14 volts. The PMA/capacitor and regulator may have the voltage anywhere from 9 volts to 18 volts. When the voltage swings up and down, the ignition stops working.
Connect a digital VOM to read voltage, and you may be surprised at what you see.

Some improvement may happen if you get rid of the capacitor and replace it with a battery.
The proper solution is to remove all of the PMA crap and use the stock alternator system with a battery.

 

[Eotnak]

Respectfully, if it's done properly with an appropriately sized capacitor and quality regulator, there are no voltage swings. An oscilloscope is what you need to measure this.

 

[retiredgentleman]

Capacitors are a very useful component when used in general electronic circuits. Whoever came up with the original idea to use a capacitor in place of a battery, on a motorcycle, was and is an idiot. I can't say it any plainer than that.
A cheap VOM will show the voltage swings. Yes oscilloscopes are wonderful devices, but most lads don't have an oscilloscope.

Quote;
"if it's done properly with an appropriately sized capacitor and quality regulator, there are no voltage swings."
Well there are hundreds of threads on this site, in which the large voltage swings have burnt out ignitions, stators, regulators, and headlights. All due to PMAs mostly using capacitors, but sometimes using small batteries.

 

[5twins]

Yes, PMA should stand for "Pretty Much Annihilated", not permanent magnet alternator, lol.

 

[jamesgs4]

i would rewire your headlight and check your ground wires.

 

[TwoManyXS1Bs]

... check your ground wires.

Ditto. When the headlight is turned on, it feeds current into its ground wiring. If the ignition shares that ground before getting to the battery, and the ground connections are iffy, then the ground potential for the ignition can have significant voltage. Kinda like a "floating ground". The ignition will then be experiencing a reduced voltage.

 

[pa-powerstroke]

I rewired the ignition on a circuit and all the lights on their own separate circuit. I have to have the headlight off to get enough voltage to start the bike but after the motor is spinning everything works great.

 

[jamesgs4]

I run an 85W headlight so I turn it off to start the bike also.