Assimilator Light...again...dead horse?

Hi Guys! My first post to this forum...although I've been lurking here intently for a year. Last September I bought the dream bike of my youth...'71 Roadster...restored to total stock by Phil Radford about 10 years ago. I've been going over a few minor things and have recently been running down an assimilator light issue. I've read all the old threads on this, and now seem to have a somewhat new twist on the problem. The original assimilator was replaced (by Phil?) with the comparable solid-state version (38706).

I always had the light glowing at any RPM and with any combination of running lights operating, as well as low voltage at the battery. I traced this to an overheated, burned connector on the yellow/green wire where it splits ahead of the rectifier at the two-into-one bullet connector. I ordered new connectors from British Wiring, put it all back together, and Voila!

...the light glows bright and consistently now!!! What the...???

I was heartbroken, as I fully expected that this would totally eliminate the problem. With what I feel are now solid electrical connections, and likely avoiding the failure issues associated with the original-type resistance assimilator, what is the next direction I should turn to?

I guess the first question to ask yourself is do you feel that your charging system is ok?
After forty eight years or so, the magnets in the alternator rotor are getting tired, and may be long overdue for a replacement.

Have you got a multimeter?
It's worth checking the voltage across the battery:

• with the engine off (12.6 volts)
• with the engine idling (12 to 13 volts)
• at about 3,000 - 4,000rpm (14 to 15 volts)

These voltages are assuming you have a good battery - note that at engine idle, you are taking out more than you are putting in.



Are you running a modern regulator/rectifier?

The Boyer Bransden Power Box for example calls out in the instructions that you cannot run an assimilator with their unit.

That's because the assimilator is monitoring alternator output, and a lot of these regulators/rectifier are shorting out the AC side when the battery does not require a charge, which results in spurious behavior on you warning light.

An easy answer is to use a charge warning light instead.
I personally like these guys as they have a unit that will light the original lamp instead of using an ugly, non-matching LED.
But there are many others available!

Well, I don't know how much help I can be because I don't use an assimilator. I have an ammeter. As I understand it, the assimilator lights up to show the charging system isn't generating enough current to carry the load, so the battery is keeping the voltage up. (temporarily) The light should go out once the rpm's rise and the system is charging normally.

So, you need to see which road to go down by testing voltage at different rpm's. If you run the bike with an voltmeter attached, you should see proper voltage rise with a rise in rpm's. If you don't see this, then your assimilator light was working properly. IF you use a battery tender (I do) when your bike is at rest between rides, then your charging system may be faulty or the rotor magnet has lost significant magnetism, with the battery tender masking a rotor/stator charging issue by bringing the battery voltage up in between rides.

If your voltmeter shows a proper rise in voltage with a rise in rpms, but your assimilator light doesn't go out then it would seem to me that the assimilator is faulty. Maybe test the voltage right at the assimilator connection to verify it's getting proper charging voltage above 2000 rpms where the light should be off. IF it doesn't go out with charging voltage applied then how could it be anything but faulty?

Understand that the assimilator senses AC voltage from one leg of the alternator relative to ground. Ground in this case is supplied by the positive side of the diodes in the rectifier (assuming stock charging system and rectifier). So it's checking both the alternator and half of the rectifier. So if you check the voltage (AC) between the green/yellow wire and ground at the assimilator and it's more than about 6 volts, the warning lamp should be off (engine running).

The battery is somewhat anemic at 12.2 at rest, likely from having been charging for who knows how long from only one leg of the alternator. Since the wiring fix, I now measure about 14.4 at anything over 3000rpm. The bike has a stock set-up of rectifier, zener, and the standard points system. All these components were replaced about 10 years ago, although, obviously, this is still old technology. I think if I ever go with an electronic ignition I would use the Tri-spark. I understand that it may be the least sensitive to low voltage issues. Is that correct?

Is this (now bright) assimilator light issue simply a matter of getting the battery fully charged to 12.65 at rest? Perhaps I am simply too impatient.

My solid state assimilator works and is 5 or 6 years old. It is an RGM one,



and the wiring is

TERMINAL CONNECTION

WL - WARNING LIGHT (BROWN/WHITE)
AL - ALTERNATOR (GREEN/YELLOW)
E - EARTH (RED)

If your voltage does not climb as the battery is being charged or defective then it will not go out, the voltage has to climb over the threshold voltage and then it goes out. At 14.4V it should be out so check its wired correctly. My red light will come back on at tickover with all the lights on.

The light should go out as soon as the engine starts. Unless the electronic gizmo is some kind of voltage monitor, and not just a replacement for the WLA. The one I have the light glows dimly at idle.

It's the 06-2054, just like kommando shows.

Dang! Now I'm going to have to leave work ASAP and go home to mess with the thing and collect more data. I'll never be able to focus now!

Nothing wrong with old technology - I would prefer to run a zener and rectifier over and above a Podtronics!!!

If you are seeing 14.4 volts at revs, then your alternator, zener and rectifier are doing their job, and if they are only ten years old, there should be plenty of life in them yet!


Yes, the Tri-Spark is much more tolerant of lower voltages than say the Boyer which really likes a tip top battery.
The specs on the Tri-Spark say 8 to 16 volts.
We have one on the MK3 and it's a breeze to setup.
The anti-kickback is a nice feature (kinder on the electric start, but I should imagine helpful for kickstarting too)
I also like the LED for setting it up and the test button.

As Maylar said, the warning light is supposed to go OFF when everything is working correctly. His light flickers at idle which is showing the typical marginal charging capacity of the commando system when idling. My bike's ammeter shows that same scenario. As soon as I hit the gas, my bike's ammeter goes to the positive and Maylar's assimilator light goes OFF, both showing the charging system is working as designed.

Your bike should react the same as Maylar described.

@o0norton0o yes, that's my point.

As i said before, at idle when you are taking out more than you are putting in, i would expect to see the light come on.
When you rev, the light should go out.

Since the OP is seeing 14.4 volts across his battery at revs, it shows that he is putting back in more than he is taking out, so the charge circuit is working.

Which means surely the issue is with either the battery (they get sulfated if left forever on a trickle charger) or with the replacement assimilator either not wired up correctly or faulty.
On the grounds the battery is at 12.2 volts and not 12.6 volts at engine off, i think that's the first place i'd be looking if it was me.

The WLA is an "alternator" idiot light. It doesn't care about battery voltage. But as you guys noted, if he's at 14.4 volts the charging system is definitely working. I suspect a wiring issue, or perhaps the output of the assimilator is shorted.

Wow, you guys are great! Thanks a bunch. This weekend I am going to get more than the two data points I have of "off" and "3000+ rpm" battery voltage, check the condition of the ground at the assimilator and the voltage directly across the AL and E terminals of the assimilator when the bike is running. The PIA is it is stuffed up under the tank and therefore difficult to get to without disassembly. I'll check and report back early next week.

Since I know I am getting 14.4 into the battery at rev, I'm wondering if the KISS principal will work here...ie black electrical tape over the light.

One last thing...is it "normal" for those bullet connectors to develop enough resistance to burn the rubber covering? This is not a particularly good place for a fire...being directly in front of the horn and under the float bowl drain plugs and all. I now have a whole bag of single and dual bullet connectors from British Electric. I'm all about absolute originality, but have you found a better trade-off for connectors?

When bullet connectors are tight and clean they work well. When the socket (female) cracks or gets corroded with age they become intermittent, and a high resistance connection can get hot. No, it's not normal - it means they need attention (replacement). Other folks will tell you to replace them with something else.

Fill your carbs up before taking off the tank - you'll be able to run the motor long enough to get the data you need to diagnose this problem.

Ron Hidu said:

Since I know I am getting 14.4 into the battery at rev, I'm wondering if the KISS principal will work here...ie black electrical tape over the light.
.........

I'm all about absolute originality, but.....

Click to expand...

You could simply disconnect the power wire to the light, "out damned spot!"
or
you could add an oil pressure sender to activate that troublesome red light. Madass 140 on this forum offers them for sale. Very good
product, not noticeable, inexpensive, easy return to original configuration, AND much more useful to know if you have oil pressure
than to know if your alternator is charging.

Ron Hidu said:

The battery is somewhat anemic at 12.2 at rest, likely from having been charging for who knows how long from only one leg of the alternator. Since the wiring fix, I now measure about 14.4 at anything over 3000rpm. The bike has a stock set-up of rectifier, zener, and the standard points system. All these components were replaced about 10 years ago, although, obviously, this is still old technology. I think if I ever go with an electronic ignition I would use the Tri-spark. I understand that it may be the least sensitive to low voltage issues. Is that correct?

Is this (now bright) assimilator light issue simply a matter of getting the battery fully charged to 12.65 at rest? Perhaps I am simply too impatient.

Click to expand...

Your charging is fine. 12.2 at rest is not terrible and depending on the type of battery you have it might be correct. If it is still 12 or higher after a couple of days of non-running, it's fine.

The assimilator is supposed to be on or off. Either yours is bad, or the wires are on the wrong terminals, or there is a miss-wire somewhere else.

If your alternator has two wires (probably does) there now way to charge "only from one leg" it takes two wires to make the circuit.

IMHO, the assimilator is silly so I eliminate it on every bike I wire, install an oil pressure switch, and use the red indicator for that.

If you determine that the assimilator is bad and you want to keep an assimilator, PM me, I have some original ones I'll never use. Or, if you want an oil pressure switch PM me, I can help with that.