‘71 Norton ignition light staying on.

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FL54

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1971 750 warning light is staying on. Previously, it wasn’t lighting at all. With the help of Dennis Mo, traced the problem to a faulty assimilator. Replaced the assimilator and now the light stays on after engine is started. Checked voltage at battery and voltage goes up when revving the engine so it is charging. Thanks in advance for any guidance.
 
Good Morning!!

Solve one problem and uncover another....

What is the actual voltage at the battery when you rev the engine?

We now know that the path from the ignition light is working as the light is on which means the assimilator is grounding it (and turning it on) when the engine is off

What should happen (to turn the ignition light off) is that the voltage on the blue arrow wire should rise to (I think) about 6.5 Volts when the engine is running.
The assimilator is a voltage sensitive relay that when voltage rises, should break the ignition light circuit and turn it off

I suggest that you check the voltage on the spade connector of the assimilator that the blue arrow plugs into, with engine off, then engine on and idling, and then reving ? (Don't unplug that connection while testing).

Dennis

‘71 Norton ignition light staying on.
 
Thanks Dennis as always for your help. That’s the story of this bike. Fix one problem and another one promptly appears. I think I got up to 14 volts at the battery when revving the engine. Right in the middle of testing, an oil line failed spewing oil all over the lift. I’ve got to replace that in about an hour when the parts store opens before I can test as you suggest.
 
When I rebuilt and refreshed my 74' Commando this past winter, a new wiring harness was part of it. I bought the bike from the original owner and he had recently replaced the assimilator unit.
I owned another 850 that the unit was fried/didn't work and it didn't bother me in the least, especially at the price of replacing it. When I rewired the 74' over the winter, for some reason the red warning light stays on after starting and never goes off. My bike is stock with turn signals and all other accessories, so I was puzzled that the assimilator light, which functioned correctly before the new harness, now stays on. New stator, new rotor, new MOSFET. Battery voltage right where it should be and voltage increases with RPM. Charging as it should.
I have LED in the warning, turn and high beam indicators, (cool running and brighter) so now I just consider the red light as the "ignition switch on" light. My 1966 Triumph Bonneville has the same set up, one lonely red light in the headlight shell telling me the key is on. I find it far more useful than a light to tell me my charging system is working. Just my 2 cents....
 
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All the assimilator does is switch the warning light off when it senses there is some AC leaving the stator it does not indicate that the system is charging.
 
Better yet, disconnect the dumb assimilator, buy and install an oil pressure sensor from Don Pender, and wire it to the otherwise useless warning light.
A dead battery is inconvenient. Lack of oil pressure is catastrophic and expensive.
 
The standard Norton assimilators do not work with modern rectifiers, I had the same problem when I rebuilt my Mk3 and fitted a Trispark Mosfet the light stayed on I tried 3 assimilators before emailing Trispark who replied that was the case but was it not stated in their fitting instructions.
 
Easiest and cheapest way, 1) does the headlight brighten up when the bike is revved, 2) push the horn button is it loud and working normally, 3) are the directional lights blinking normally . And old Aluminum "tube type" assimilators could be opened up and cleaned and adjusted to make it work again IF it is in decent condition inside. When the light stays on , I just consider it a ignition /key is turned on, providing one of the three tests is OK.
 
"Improving Classic Motorcycles" tri color LED works great for me. Ignition on red, start and a bit above idle goes green if all is well. Graham
 
possm said:
The standard Norton assimilators do not work with modern rectifiers, I had the same problem when I rebuilt my Mk3 and fitted a Trispark Mosfet the light stayed on I tried 3 assimilators before emailing Trispark who replied that was the case but was it not stated in their fitting instructions.
Click to expand...
This would explain what I experienced.
 
I long ago dumped the assimilator for a voltage indicator light. Amber below 12.45, flashing red at increasing rates below 12.25, steady green above 13.2, alternating green and red above 15. Assimilator only tells if AC coming out of alternator, next to useless.
For oil pressure I added a gauge, it's saved me a couple of times when the conical seal split in the timing cover.
With a 3 ph alternator and series regulator light just goes amber at traffic light unless heated gear on. Goes green just riding away. Less money than a new assimilator, gives useful information.
 
Dennismo has been a great help in troubleshooting the issue. I replaced the assimilator because it was faulty. We’re trying to find out if the new assimilator is of the old style or solid state. Previous reply reported that the stock assimilator is incompatible with a solid state rectifier. Would it follow that a solid state assimilator is incompatible with a stock rectifier?
 
Just wanted to close the loop on this thread to help anyone down the road with a similar problem. I returned the solid state assimilator and found a NOS assimilator on eBay. It arrived yesterday and glad to report it’s working as it’s supposed to. I guess the take away is the old and new technologies are incompatible with each other.
 

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