on my 87 e350, i'm having a problem with the alternator warning lights flashing on and off randomly. i'll start by describing my custom system

to start with, i upgraded to a 3g alternator. after a week or so, the light popped up because the 1-wire connector next to the 3-pin was loose. i replaced the connector and the problem went away.
a few months later i decided to install a second 3g alternator on a divorced system to power my inverter and its huge battery. this system can be connected to the starting batteries through a large solenoid, but usually remains disconnected.

for some time now, the warning light for #2 will occasionally pop up for a few seconds, usually at low speeds. other days (like today), its on over half the time, flashing back and forth randomly. when it had been on for a minute, i decided to turn on the switch to connect the 2 systems, then the lights for the first alternator joined in this flashing game, but not synchronized to each other.
i've checked several times that all connections are tight, and i'm having no luck finding my problem

any thoughts?

 

Do you have voltmeters or ammeters on either of those systems? Sounds like there is too much of a demand on the second generator. The warning light is controlled by the regulator. One lead to the bulb is DC+ from the battery, switched thru the key switch. The other lead to the bulb goes to the regulator. When it ain't charging, this circuit is pulled low (to DC common, ground), which lights the bulb. When there is output from the alternator, this circuit goes high (~14VDC) which provides no path for the bulb to ground thru, so it goes out since there is no potential across it anymore.

Somehow you have a condition where the output voltage is dropping down so low that the regulator effectively considers it to be a no-output situation. The way you describe your setup, I'd say you're overloading that second gen. 130A rated don't mean 130A continuous, unless the manufacturer of the alternator specifically says so. Being a factory Ford part, I'd say it AIN'T rated at 130A continuous. That's ~1.8kW (1800 watts) at 14V, something it probably wasn't designed to do for long... and keep in mind that you mentioned this was at low speed which I'm guessing you mean low engine speeds. Every generator/alternator has a certain speed at which it'll put out it's rated power. Below that, don't expect much because they drop out fast.

The warnings from both systems after you closed the contactor and connected the 2 battery buses together tells me that the load there is too much for both alternators to handle, again remember this is at low engine speed and they are probably below their rated running RPM. I'd connect both an ammeter and voltmeter on that second system, open your isolation contactor, and see what's really going on with it.

 

Believe it or not, the great 3g has some known problems also. I would check the brushes and the brush holders. The brushes can wear and the brush holders are known to melt sometimes.

 

the load on the system isn't excessive, so i don't think that was it. on the trip when it was lighting up the most, i'd only been pulling 20 amps off that battery for about half an hour, and had almost no load on the system while driving. other days i'll draw a lot more power without having it flash at me.

so far i don't have any gages on either circuit, but i intend to get them one of these days.
i was thinking it might be some kind of internal problem, but i didn't know about their tendency to have problems with the brushes. i'll look into that, thanks