generator light troubleshooting
Thread Starter
Racer
Joined: Feb 2012
Posts: 421
Likes: 27
From: Harrisburg PA
generator light troubleshooting
Hello all:
I purchased a '77 about a month ago.
The generator light is on, and the voltage gauge shows nothing happening.
I pulled the alternator today, took it to advance, and it tested bad (DC volts, whatever that means)...
I replaced it with a Powermaster unit.
The generator light is still on, and there is till nothing happening on the Voltage gauge.
I put my circuit tester on the battery terminals, engine running, and it read 14.27, which means the alternator is charging, correct?
Where do I start? It is also worth mentioning that the temp gauge does not work (already tested the sending unit, and that is not the issue), the fuel gauge "floats," and the oil gauge seems to work (but also does not go back to 0 when I shut the car down...not sure if it is all related, and I just need a new printed circuit or what...
How do I troubleshoot? I'd really like to drive the thing with some peace of mind at least once before I put it away for winter!
Thanks!
I purchased a '77 about a month ago.
The generator light is on, and the voltage gauge shows nothing happening.
I pulled the alternator today, took it to advance, and it tested bad (DC volts, whatever that means)...
I replaced it with a Powermaster unit.
The generator light is still on, and there is till nothing happening on the Voltage gauge.
I put my circuit tester on the battery terminals, engine running, and it read 14.27, which means the alternator is charging, correct?
Where do I start? It is also worth mentioning that the temp gauge does not work (already tested the sending unit, and that is not the issue), the fuel gauge "floats," and the oil gauge seems to work (but also does not go back to 0 when I shut the car down...not sure if it is all related, and I just need a new printed circuit or what...
How do I troubleshoot? I'd really like to drive the thing with some peace of mind at least once before I put it away for winter!
Thanks!
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
I have a suspicion your wiring is in fact incorrect for the regulator on your car, the two wires reversed......this is verry common for sharks, GM used very similar color wires on the vettes, and not so much on other in the lineup......
SO, to unplug the 2 pin connector, and with the car OFF, measure what should be a RED wire it should be live with battery voltage....
All the replacement connectors I have seen at the parts house are coded the more common color codes....RED is the most clockwise pin as viewed from the back of the alt......that is the one that is alway hot at whatever voltage ....
the WHITE wire is only live through the bulb, and is pulled down to zero to light your dash idiot light when the alt is not putting out.....most of the dash lights are rather dim if the two wires are reversed.....
but you need a voltmeter....to check this stuff.....try Harbor Freight for a cheep VM you can keep in the car.....
SO, to unplug the 2 pin connector, and with the car OFF, measure what should be a RED wire it should be live with battery voltage....
All the replacement connectors I have seen at the parts house are coded the more common color codes....RED is the most clockwise pin as viewed from the back of the alt......that is the one that is alway hot at whatever voltage ....
the WHITE wire is only live through the bulb, and is pulled down to zero to light your dash idiot light when the alt is not putting out.....most of the dash lights are rather dim if the two wires are reversed.....
but you need a voltmeter....to check this stuff.....try Harbor Freight for a cheep VM you can keep in the car.....
Thread Starter
Racer
Joined: Feb 2012
Posts: 421
Likes: 27
From: Harrisburg PA
I do have a voltmeter...
So, I'll check and see which one is hot with 12 volts with the car off...
The 12 volt wire (with the car off), goes on the right most (when viewing from behind), correct? If I read your message correctly...
So, I'll check and see which one is hot with 12 volts with the car off...
The 12 volt wire (with the car off), goes on the right most (when viewing from behind), correct? If I read your message correctly...
Thread Starter
Racer
Joined: Feb 2012
Posts: 421
Likes: 27
From: Harrisburg PA
I have a suspicion your wiring is in fact incorrect for the regulator on your car, the two wires reversed......this is verry common for sharks, GM used very similar color wires on the vettes, and not so much on other in the lineup......
SO, to unplug the 2 pin connector, and with the car OFF, measure what should be a RED wire it should be live with battery voltage....
All the replacement connectors I have seen at the parts house are coded the more common color codes....RED is the most clockwise pin as viewed from the back of the alt......that is the one that is alway hot at whatever voltage ....
the WHITE wire is only live through the bulb, and is pulled down to zero to light your dash idiot light when the alt is not putting out.....most of the dash lights are rather dim if the two wires are reversed.....
but you need a voltmeter....to check this stuff.....try Harbor Freight for a cheep VM you can keep in the car.....
SO, to unplug the 2 pin connector, and with the car OFF, measure what should be a RED wire it should be live with battery voltage....
All the replacement connectors I have seen at the parts house are coded the more common color codes....RED is the most clockwise pin as viewed from the back of the alt......that is the one that is alway hot at whatever voltage ....
the WHITE wire is only live through the bulb, and is pulled down to zero to light your dash idiot light when the alt is not putting out.....most of the dash lights are rather dim if the two wires are reversed.....
but you need a voltmeter....to check this stuff.....try Harbor Freight for a cheep VM you can keep in the car.....
OK--just tested with voltmeter, and red wire does have 12.27 volts, engine off, no key in ignition...It is plugged into the right most terminal (clockwise position form rear)...
What's next?
Thread Starter
Racer
Joined: Feb 2012
Posts: 421
Likes: 27
From: Harrisburg PA
it may be worth mentioning that the gauge has worked, and the light off when I bought the car a few weeks ago. The issue was first "intermittent" and has now become "persistent." Not sure if that makes a difference or not...Nothing's changed--it would work OK sometimes, and not others--now, never at all...
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
Because the light goes off when the wire is unplugged from the alternator, you have proved that the wiring for the light to the alternator is good. You also had battery voltage at the other wire in the connector. Engine running, what voltage is at all 3 of the alternator wires?
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Pro
Joined: Apr 2009
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Likes: 1
You need to check the wire that lights your BATT light on your dash to see if it is grounding somewhere else other than the voltage regulator. The easiest way to do this is to make another test light with a bulb socket that will fit your current BATT bulb. I forget what the number is that designates the light bulb on your BATT light. Someone else on here will know. Pick up the bulb socket at your favorite auto parts store. Most likely Pep Boys or Autozone. Then connect that in place of the wire coming off your alternator that feeds your BATT light. It will need to be a single wire bulb socket. it only has to be 12" or less. Once hooked up, when you turn your ignition to "on", the bulb will light because of the ground from the voltage regulator. Once the car is started and the voltage regulator starts to read voltage, the light will not be grounded any longer and will go out. If that happens with your test light, your BATT wire is grounding somewhere you don't want it to be.
Good luck.
Good luck.
Thread Starter
Racer
Joined: Feb 2012
Posts: 421
Likes: 27
From: Harrisburg PA
Because the light goes off when the wire is unplugged from the alternator, you have proved that the wiring for the light to the alternator is good. You also had battery voltage at the other wire in the connector. Engine running, what voltage is at all 3 of the alternator wires?
red = 14.30
white = 0.00
red on back of alternator (main connection) = 14.33
connector plugged in, probing the connector:
Red = 14.3
white = 14.3
red on back of alternator = 14.33
Yes, the gauge reading 0 and the generator light coming on issues happened at the same time.
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
Definitely check the gauges fuse, as stated earlier, a bad connection there could be the issue. The bulb lights because of a voltage differential. I didn't clarify the earlier question about the light, does it come on with the key on, engine off?
Thread Starter
Racer
Joined: Feb 2012
Posts: 421
Likes: 27
From: Harrisburg PA
The light does NOT come on with the key on, engine off. The gauge also does not move at all with the key on, engine off...
if this turns out to be as simple as the fuse, I will be somewhat embarrassed that i did not check there first...
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
I was guessing the light wouldn't come on because you had 0 volts in the plug for the white wire. The reason the light comes on when running is that the alternator then has more voltage than the light circuit and is trying to power up the volt gauge also. May be a problem with the printed circuit on the back of the gauges or the plug that goes into it.
Thread Starter
Racer
Joined: Feb 2012
Posts: 421
Likes: 27
From: Harrisburg PA
I'll check the fuse later today, and then pull the gauge cluster apart--probably in the spring to see what's what...Like I said, the temp gauge does not work, either, the fuel gauge floats, the oil gauge seems to work, but I think is reading high, and there are no lights at all in the cluster...
Thanks for the help, and I'll definitely dial back in when I get a chance to mess with it some more!
Thanks for the help, and I'll definitely dial back in when I get a chance to mess with it some more!