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I've done some thread searching as well as googling, and I'm stumped. At this point everything seems ok, but the battery light is on while driving. What I've done:
New battery - the old one had gone dead from lack of use one too many times, had it on a battery charger for a few days and never fully charged.
Replaced the choke relay - it was buzzing and the choke light stayed on. I really thought this would fix it based on other threads. Choke light no longer stays on and the relay isn't buzzing.
Pulled the center console and inspected the PCB. One of the connectors was tweaked causing oil pressure to be pegged to the right. I smoothed it back then super glued down all the ends where the plug connects just to keep everything straight while reconnecting. Oil pressure gauge fixed.
Voltage across battery when car off is 12.7. Voltage when car is running is 14.1 - doesn't matter if at idle or rpms are up.
I believe the Gen Light refers to the alternator. Mine was doing something similar and I pulled the wires connected to the Alternator and and reconnected them better and it fixed it.
I would love to know which wire was tweaked for the oil pressure gauge that fixed yours, mine is doing the same as yours was, always to the right.
I've done some thread searching as well as googling, and I'm stumped. At this point everything seems ok, but the battery light is on while driving.
Voltage across battery when car off is 12.7. Voltage when car is running is 14.1 - doesn't matter if at idle or rpms are up.
What am I missing?
There are a few things that could cause this. Is this the only odd thing that the light does? My gut says faulty voltage regulator, but could be something else. Do you have a FSM?
I believe the Gen Light refers to the alternator. Mine was doing something similar and I pulled the wires connected to the Alternator and and reconnected them better and it fixed it.
Oh ya, I forgot to mention I did this as well. I tried to clean the connector 'cause it was a bit gunky. I think I have a good connection now, but it's easy enough to double check. The other connections on the alternator felt pretty solid, but I didn't trace them to check connections on the other end of the wires.
I would love to know which wire was tweaked for the oil pressure gauge that fixed yours, mine is doing the same as yours was, always to the right.
Pull the center console, look at the spot on the printed circuit board where the connector "plugs" in. Bottom left copper connector strip was bent out of shape as if it was pushed aside when the connector was plugged in. This is what I straightened then super glued in place. Such a cheap crappy design, but I guess it works and saves a few bucks.
Originally Posted by Antz81
There are a few things that could cause this. Is this the only odd thing that the light does? My gut says faulty voltage regulator, but could be something else. Do you have a FSM?
Ya, at this point the bat/gen light being on is the only odd issue I'm having. You could be right about the voltage regulator, but I'm not completely convinced - I'm getting a solid consistent 14.1 volts throughout the rpm range.
I'll double check the connector at the alternator itself, then I'll drive around and try to pay close attention to how dim/bright the light is and what makes it go dim/bright. I don't have a FSM, just a Haynes manual. I try to avoid working on my cars now, any real mechanical work I'll take to a shop.
I actually replaced the choke relay already - it was buzzing and the choke light would stay on or flicker. I really thought this was the issue, but choke light is fixed and batt light isn't. I didn't check the fuse though, I'll add that to the list. I took it out to lunch and really paid attention to the light, maybe more details will help:
At idle the light is very dim, it almost looks like it's off, you have to look closely. This is T-ops off in the sun, so maybe at night it's more obvious.
It gets brighter as RPMs rise. Not full on bright, but definitely brightens up with RPMs.
It flashes brighter with turn signals.
Turning on headlights gets it to nearly full bright, considerably brighter than anything else mentioned.
Here is what the manual is showing for Gen Light on while Engine is running. There was also a note for battery being undercharged will cause this, you just replaced the battery but if the alternator is not charging it effectively it could cause.
Thanks for that. I haven't driven much at all since replacing the battery, just short jaunts, so I connected my trickle charger.
Not sure how helpful that page is, but thanks for posting it. Once I've ruled everything else out and I'm really at step 3 I may as well just replace the alternator. It's probably the original and I just don't want to go digging into it hoping I get it back together correctly to save $80 or whatever.
The kicker is I'm seeing 14.1 volts at the battery with engine on so I've convinced myself that the alternator itself is ok.
Yea, Alternators aren't to bad to replace price wise. That is what the dealer would of done if you brought it in to them back in the day, it's from the GM Chassis Manual. Of course unless you are the 1st owner who knows what has been done since then with the wiring, aside from age.
Well, that page doesn't take into consideration things like the choke relay/fuse, bad wiring connections, problems with the PCB and who knows what else. All those weird things that happen with a 35 year old car that people figure out over the years.
Thanks for that. I haven't driven much at all since replacing the battery, just short jaunts, so I connected my trickle charger.
Not sure how helpful that page is, but thanks for posting it. Once I've ruled everything else out and I'm really at step 3 I may as well just replace the alternator. It's probably the original and I just don't want to go digging into it hoping I get it back together correctly to save $80 or whatever.
The kicker is I'm seeing 14.1 volts at the battery with engine on so I've convinced myself that the alternator itself is ok.
Before you just throw parts at it, what voltage do you get on the red wires at the alternator? Does the one in the plug change with rpm, or load? Is the ground clean and tight?
Before you just throw parts at it, what voltage do you get on the red wires at the alternator? Does the one in the plug change with rpm, or load? Is the ground clean and tight?
Throwing parts at it is exactly what I'm trying to avoid. I'll check the voltage at the alternator in a day or two - can't get to it today.
Originally Posted by TimAT
Step 3 is an easy one- touch that tab on the regulator to the case with a screwdriver and it puts the alternator into "FULL OUTPUT" mode.
Right - but once you start following step 3 you eventually get to "replace voltage regulator" or "repair generator." The decision tree doesn't lead anywhere else. This gets me back to where I'd rather just replace the whole thing than take it apart and try to fix it.
Before you just throw parts at it, what voltage do you get on the red wires at the alternator? Does the one in the plug change with rpm, or load? Is the ground clean and tight?
~14.4 at plug, doesn't change with RPMs. ~14.6 at main big red wire, doesn't change with RPM. With lights on, the load that seems to make the biggest difference with the batt light, voltage drops roughly 0.1. Initially turning on the headlights does appear to cause a bigger drop for a fraction of a second - my meter drops then almost immediately levels back out.
With battery fully charged via trickle charger, no difference.
~14.4 at plug, doesn't change with RPMs. ~14.6 at main big red wire, doesn't change with RPM. With lights on, the load that seems to make the biggest difference with the batt light, voltage drops roughly 0.1. Initially turning on the headlights does appear to cause a bigger drop for a fraction of a second - my meter drops then almost immediately levels back out.
With battery fully charged via trickle charger, no difference.
Ok. That eliminates some wiring issues. Only things left in the 81 service manual is a test of the max output (in amps) but this will only tell you to repair the alternator or replace the regulator.
I personally would open it up and do more tests and just replace what is needed, but that's up to you.
I'm not sure how to test max amps. I suppose I can put a load on the system then check amps at the battery, but I can't max out the system. My A/C didn't work when I bought the car back in '94, and I never bothered to fix it - pretty much t-tops off nice weather driving only. Otherwise I can just do lights on, wipers on, radio on, turn on flashers...
Then there is the issue that I don't know what I'm looking for. I'm guessing it's a 70amp alternator??? What amps would I be looking for?
Took it to autozone and had them test it. I'll be the first to admit I don't trust them 100%, but they hooked up a special piece of equipment and ran it through a series of tests - starting with the battery, through the startup, checked charging, tested voltage, diode testing, and finally amps under load. Passed all checks.
Took it to autozone and had them test it. I'll be the first to admit I don't trust them 100%, but they hooked up a special piece of equipment and ran it through a series of tests - starting with the battery, through the startup, checked charging, tested voltage, diode testing, and finally amps under load. Passed all checks.
What am I missing?
Only thing I can think of is a fault in the regulator that the tests at autozone don't show.
07-12-2017, 12:26 AM
'81 w/battery light (gen light)
