Amp light full red on startup?

[Bigbunt]

This is one of those little mysteries that I'm only asking about because it's intermittent and has the potential to leave me stranded...
Every once in a while when I start my B20 in the morning, the amp light comes on full bright red. Normally it does the flickery reddish behavior which I've gathered is completely normal, but this is unblinking. It hasn't ever stayed on past the end of the driveway but my concern of course is that I'll go out at night and it'll come on and stay on and leave me without a charging system.
I'm kind of assuming my regulator is a little sticky but not sure if that is it and if it is, can it be freshened up or should it be replaced or whatever.
This car still has a generator which seems to be fully functional, with lots of life left in the brushes...but it is (probably) 48 years old.
This novice defers to the learned ones among us... Thanks for any thoughts.

[Ron Kwas]

Bb;

AMP Indicator can come full ON for two very different reasons (see: http://www.sw-em.com/AMP_Indicator_ON.htm ) but since it is going OFF without intervention at Fuse 1, it is definitely not due to Condition 3.

AMP indicator should go OFF almost immediately after Starting, as soon as RPMs rise off idle and CH Sys starts putting out, so your action is actually not normal (just normal and typical for your vehicle)...if it takes longer than that, or higher RPMs, it indicates cut-out relay in Regulator is not closing as soon as it should. Immediate cause is low Ch Sys output.

These symptoms are most often a result of worn Generator Brushes (resulting in low contact pressure to commutator) , or poor contact between Brushes and Commutator (resulting from that dark surface coating on copper [ it has a specific name, which I used to know back in my DC Motor days] which Brushes are immediately cutting through due to low pressure - see above).

I recommend you first procure some replacement Brushes, to have them on hand...but you might get some temporary relief by simply removing Brush access band (Gen in-situ, Battery disco) and cleaning Commutator to bright shiny copper.

Cheers from down(up) the Road

[Bigbunt]

Ron, I had the generator out when I did the clutch this winter and took off the end of the housing and checked out the brushes and they appeared to have a lot of life left judging by length remaining. Everything seemed fine and I took the opportunity to clean everything up. Could a compromised wire to regulator do the same thing? And would this be a typical,way for the regulator to begin to fail maybe?

[Ron Kwas]

Bb;

"Compromised wire"...I suppose anything's possible, and you should go ahead and preemptively clean and refurb all connections related to Ch Sys in sight, but I wouldn't be surprised if this did not remove symptoms...sorry...

It's been a while since I had a new Brushes in my hand...perhaps someone could measure the working height of new ones and post...

Related Story: I specifically recall years ago...Leif Anderson, while visiting the US and joining us for the Mt. Snow Volvo Meet...when someone's Ch Sys failed due to short/worn Brushes, he nonchalantly walked by a bunch of guys up to their elbows in underhood Volvo dirt and Generator dust in the parking lot of an event (when we should have been hobnobbing and drinking Chablis with everyone else) and suggested simply putting the same Brushes back into guide with a 90deg twist, as they were worn shorter than in the wider dimension...this made them taller and able to get more preload force from the Spring...and it worked!...to return function of Ch Sys as a temporary fix...long-term, this leaves a step-wear in commutator so requires proper service including removing any step from commutator ASAP, but is a good emergency road fix in a pinch.

Remember: Output goes through Brushes in a Gen...poor connection...poor Gen output...simple as that!
Cheers

[Bigbunt]

Hey Ron, well fortunately for me, light went on and stayed on while at home so I just ordered brushes from VP per your recommendation. Upon looking at photo records I realized it was my starter motor that I had examined brushes on! Getting soft in the head! Hopefully,will get the parts Saturday. I'm sure they could use a refresh anyway.
The only reason I mentioned "compromised wiring" was that this car had a brief conflagration under the hood which took it off the road before I took possession and some wire insulation is a little sketchy. It runs like a champ though and all will be gone through over time but it's in the back of my mind to replace any singed wiring. That'll probably happen this winter when I do some inner wing repair and fender repair... A major goal is making sure body isn't rusting to death...!

[Derek UK]

New dynamo brush shown.


Brush should work until the spring comes into contact with the housing. Brush will get rather sparky at that point which you might be able to see if you look at the brush end of the dynamo when it's dark. Might also mess up your radio.
I had this red light problem with my wagon. It would go out after you gave it a boot full but eventually decided to stay on all the time. Brushes were fine so gave that one and two others to a rebuilder. He said there was a fault in mine and one of the others. Spruced up the OK one and fitted it. Still don't think this one is 100% and the light will still occasionally come on full for a few seconds on start up. I'll keep an eye on it. Original regulators have had a long and hard life. New ones are expensive............