1990 Civic DX, 4 Dr., 5 Sp., 1500cc

I've got the Battery light on in the dash pretty much all the time now.
It was intermittent, not coming on for a half hour or so after startup,
and either coming on or going out under certain engine load conditions,
but now it's there all the time.

Honda Service Manual has an Alternator testing procedure that first
begins by removing the main connector from the Alternator and checking
for voltage to ground at two different pins inside the connector.

Unfortunately, mine fails the second of those voltage tests, and in that
case the test procedure refers you to the ECU troubleshooting section at
that point. Which is a bit of a problem because I don't have the special
interface cable needed to access the ECU circuits for test purposes, and
get this: the test procedure for the ECU says "Substitute known-good
ECU; if problem disappears, replace ECU" at various points in the
procedure.

Hmmm. I haven't priced it officially yet, but that thing costs in the
neighborhood of $250 bucks! I can't afford to buy one just for testing
and troubleshooting!

And if I *had* a known-good ECU, what would I need a testing procedure
for in the first place? Swapping it out would *BE* the testing procedure!

;-)

I think the problem is that the ECU has an economy circuit in it that
shuts down the Alternator under certain load conditions to save fuel.
Pretty neat idea, except when it malfunctions!

My question: How can I determine for certain whether it is the ECU
malfunctioning, or if it's some other load/condition sensor giving it
faulty data? And I suppose it still could be the Alternator itself...

Keep in mind I don't have a "known-good" ECU to follow the official
diagnostic procedure, and I'm not sure if I can go buy one, use it for
testing, and return it if it turns out not to be the culprit.

Any ideas?

;-)

Thanks,

--Charlie Henderson