Durango_Boy

Okay, I kind of understand what this light is there for, but it seems to be there to indicate problems with the electrical system and mine is showing me some funny things.

Before installing a noise filter inline with the harness 12V wire from the BAT terminal, the GEN light would occassionally light up when the RPMs were running high. Say, 2500+. Idling it would not light, and it would only flicker when the RPMs jumped past 2500.

After the noise filter, the GEN light blinks a lot faster, and at all RPMs...even idle.

It never stays on.

History: The GEN light has always flashed or flickered at high RPMs through THREE alternators. The stock one, a 135 SI alt, and this new CS130 alt. The only change that I have veer seen is now that the noise filter is installed.

I'm going to pull it out as it didn't do anything anyway, and wire it back the way it was.

My question is why, when the alternators are changing, does the GEN light continue to flicker, and what is it indicating is wrong when it flickers without staying on?

I have searched various tech sites for these answers but no one has a dead on description.

...Roger...

You have 2 suppliers of power -the battery and the alternator.When the battery is the supplier the light will be on.The light is a normally on light-the light is turned off when the alt.matches or excedes batt. voltage.

Durango_Boy

So basically, before the noise filter was in place the voltage was being exceeded by the alternator and it would flicker. Then after the filter it was lower than battery voltage?

Since I'll be taking the filter back out, I assume it'll go back to it's normal operational voltages.

Do I have to live with the GEN light flickering and is this something I need to worry about? Is it saying it's getting above 15V or something and I need to worry about the battery?

I'm Batman

That's weird...mine does the normal thing and goes out after the alternator gets up to speed.

mrvette

Some time ago I lost the only schematic I had of the SI series regulators...the white internal unit with the two spade term arranged...-- when the unit is wired correctly, like in my '72, that I put a light into my car, instead of that resistance wire, i'ts now finally in the dash with a red lens on it.....it's wired to the typical aftermarket white lead, or least clockwise viewed from backside....the other typical thicker red wire on that connector goes to the MOST clockwise and is picked up off say the Horn relay or maybe another part of the harness with an individual sense wire to it, this is critical to be wired off the HARNESS to that red wire/terminal as that specifically determines the amount of charge the system sees......

I finally took the time some years ago to sit down and find out WTF was going on with the SI regulators, and ran some specific tests proving what I say......they will react the same in any car....even a foreign import, boat, Ford, Mopar.......

NOW, you have a CS series alt on there, and I can't for sure say what the wiring is....I just remember my '87 vette had 3 alts on it in the 3 years I owned it, and the reg had some 5? wires going into it from the harness.....I never got into it much as I was too discusted constantly fixing that damn car, so finally dumped the POS.....bought my '72 here and been happy doing my OWN work MY way, not maintaining someone elses mistakes.....

IMO...put a SI in there again....wire it up, and see what happens...

mrvette

the light should go out soon as engine is running....600 engine speed is enough.....

Durango_Boy

You guys are right, before the filter was added the light would come on initially as usual and then go out within seconds. But...when RPMs were high like I was really stomping on it, the GEN light would "Flicker" without actually staying on.

With the filter, the GEN light comes on and goes out normally BUT continues to "Flicker" no matter the engine speed.

I'm taking the filter back off, but now am wondering why the GEN light "Flickers" at high RPMs.

dannyman

Light on means alternator output is less than battery output. Flicker indicates a charging problem.

Durango_Boy

With three alternators in a row? A stock SI, a modified 135 amp SI, and a new stock CS130?

Seems odd that all three would have problems. No, the battery is new too.

Is there a problem with the stock harness that can damage the diodes in an alternator?

...Roger...

Matt I thought you had a single wire gen.Maybe not.
Sounds like your letting this gen light confuse you.Its just a bulb with 12 volts on the dash end and seeking ground through the brown wire going to the alternator.(like a test light) So the only time its going to come on or flicker is when the brown wire gets a ground. The ground should come through the fields in the alt. It can also get a ground by the brown wire being pinched or being bare.On the back of your center cluster is a printed circuit that could be a problem for the grounding of that brown wire.You said you have had several alt.on the car and they all do it,that would lead me to believe something else is attached to the brown wire somewhere.I'm pretty sure on your 77 that brown wire is dedicated to the Gen light unlike earlier years that used the brown wire circuit for other power acc. like the blower.and other key on items.The brown wire should be solid all the way to the alt. except for the bulhead connection.

mrvette

How many alts on the car?? can only run ONE at a time no combo of any will work....they will talk to each other....serious regulator interaction....

and the only wiring error that can wipe an alt is to have that lightbulb shorted out, effectivel hard wiring it to even a switched +12, cause you flash that guy enough or engine goes too lo for any reason and alt tries to take that ~20 amp fuse to ground and reg in there says OH CRAP, and i'ts the fuse.....no good anymore....

IF You have bad bulkhead/bulb/ connections you may well get some sort of silly indications.....old as these cars are, most any type electrical problem can occur....mostly open/he resistance connections due to corrosion....terminal crimps on once naked copper now high resistance....since it's signal wires with no serious current tothem they maybe never burn up...just give you buzzy problems like the old electronics they are.....

which is why some 6 years ago, I gave it up, decided to keep the car no matter hell over....and took it down for a 6-8? month overhaul and total change out of one boatload of stuff.....r/p steering, total rewire MY way, floorboard modifications, dash changes, engine mods....suspension crap....I can't EVEN remember what all....even the interior was gutted, top removed....

Durango_Boy

You're right about the brown wire as I ran into that problem when I changed gauge clusters. The previous owner had digital gauges installed and cut the original pig tail off. I found as stock one and wired everything back up correctly. I checked to make sure the plug was working properly and that it went straight from the bulb to the alt plug.

Near as I can tell it's all wired correctly.

davidm_comp

I'm not sure how you have the light wired up, but when I swapped out to my cs144 alternator the only way the alternator worked was when I put a 330 ohm resistor in the brown wire and then hooked it up to an ignition source

Durango_Boy

Right, and the way I understand it is that the GEN bulb IS the resistance the system needs to function. Trust me, the alt is working great if not too well. It's running in the upper 14V+ range.

Z-man

The GEN light bulb IS the resistance. You can run a resisitor in parallel so that nothing is damaged if the light bulb ever burns out.

kb2fzq

When you say "upper", are you saying near 15V.....that seems pretty high to me....do you have an external regulator or is it in the alternator or is it a generator? I'd question that high voltage as a possible cause or contributor to your problem....
Just my 2 cents......

theoUK

Well the gen light should just have 14V either side of it when your alt's running properly, so you have a potential of 0V across it, ie no light.

Any time it flickers on, it's because the voltage at one side or another (either the alt terminal side or the ign switched hot side) is momentarily dropping in relation its buddy. So it could be one of the wires chafing to ground somewhere, or perhaps the alt terminal voltage spiking (which has the same effect, ie creates a Voltage difference from one side of the bulb to the other)

It gets confusing because unlike most other bulbs on these cars, current can run both ways, depending on the voltages present at each side.

You know what you could try? Take the old knackered wiring out of the equation and wire in your own temporary idiot light. Remove the gen light (brown) wire from the two-pin plug on the alt, and just insulate and leave it loose. Then run a new wire from that pin, through a small bulb, then off the bulb to a IGN SWITCHED HOT source. The light is your new gen light, but is running on your own, known good wire. If the flashing still occurs, then either the alt's spiking or there is some problem with the ignition switch terminal you used to feed the other wire. If the flashing stops, you have some poor connection in the loom (good luck if that's the result!)

theoUK

Yeah the current that's drawn by the light when you turn the key on is what "excites" the alt and starts it charging. Without that it'd never begin to charge.
14.5V or more should be ok (would be a bit concerned over 15V)

...Roger...

Excellent Idea

"the current drawn by the bulb" ??? Matt is your gen. bulb an original type?You didnt put in some kind of LED or other type of bulb with a different resitance than stock did you? If you did it could be driving the regulator crazy.Your dash lighting bulbs can be varied but not this one !!!

theoUK

Good point about needing the "right" bulb.


Yeah, the point of the external wiring is to totally get rid of the old wiring in your troubleshooting. The tricky thing here is the fact that it's hard to know what voltage is changing to cause the flicker. It's either:

1. Alt side getting high with respect to the ign switch side, which means either an upward spike from the alt or momentary short to ground on the ign switch side
2. Ign switch side getting high with respect to the alt side - which could mean there's a momentary short to ground in the wire between the bulb and the alt.

It'd take about 5 mins to replace the wire and bulb with an external one, and should be a pretty conclusive test of the stock wiring. If it still flickers, then at least you could put a voltmeter across the bulb (one lead to each side) and see what direction the current's running, (which tells you if it's an alt voltage spike or a short to ground on the switched ign side)