Author Topic: no spark/ no power to coils  (Read 1197 times)

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Offline Llanier44

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no spark/ no power to coils
« on: September 30, 2025, 07:47:08 PM »
I don't have spark on my 71 CB500K.  It will turn over with the electric start, but no spark.  There is continuity through both points, but no power to the coils.  I tested this by turning my key on, putting the kill switch to the on position and checked the female connector for the black and white striped wire. Since my test light didn't turn on, I am thinking that I don't have power going to the coils.  The bike has a new wiring harness, a new battery, and new coils.  Where should I exert my next efforts to determine why I'm not getting power to the coils?  I know that after I (hopefully) figure out how to get power to the coils, I need to test to make sure I am getting power through the coils, but first things first.  If I'm not getting power TO the coils, the coils aren't (yet) the problem of no spark.  Thanks for any advice and counsel on this. 
Isaiah 26:3
Stage IV cancer survivor (2X)
On mission to love God, love people

Offline scottly

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Re: no spark/ no power to coils
« Reply #1 on: September 30, 2025, 09:02:06 PM »
The kill switch should have a black wire that supplies power into the switch when the key is on, and a black wire with a white stripe that supplies power to the coils when the switch is on. Check to see if there is power getting to the switch.
Don't fix it if it ain't broke!
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Offline Llanier44

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Re: no spark/ no power to coils
« Reply #2 on: October 07, 2025, 10:19:14 AM »
OK. I have power on that black wire in the kill switch assy…what now?
Isaiah 26:3
Stage IV cancer survivor (2X)
On mission to love God, love people

Offline scottly

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Re: no spark/ no power to coils
« Reply #3 on: October 07, 2025, 10:26:26 AM »
Do you now have power on the black/white wire from the kill switch when the switch is on?
Don't fix it if it ain't broke!
Helmets save brains. Always wear one and ride like everyone is trying to kill you....

Offline Llanier44

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Re: no spark/ no power to coils
« Reply #4 on: October 07, 2025, 12:35:55 PM »
I didn't see a black/white wire in the switch assy, just a black one.  But I can double check.
Isaiah 26:3
Stage IV cancer survivor (2X)
On mission to love God, love people

Offline bryanj

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Re: no spark/ no power to coils
« Reply #5 on: October 07, 2025, 04:18:50 PM »
If there aint a black\white its the wrong switch or damaged
Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!

Offline Dr. Frankenstein

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Re: no spark/ no power to coils
« Reply #6 on: October 07, 2025, 04:44:55 PM »
+ One on what Bryan said - Man, I hate electrical stuff. But at least that's the simple stuff.