Question: choke light and battery light

[tman1029]

have an 1981 vette in which the choke light and the battery light stay on after starting. I have replace the battery and the alternator. and they are both still on. I unplug the alternator and both lights go out if I unplug the choke the choke light goes off. I have taken the center console apart and it looks good. I am running out of ideas on what this can be. anyone have an idea please?

 

[LLC5]

have an 1981 vette in which the choke light and the battery light stay on after starting. I have replace the battery and the alternator. and they are both still on. I unplug the alternator and both lights go out if I unplug the choke the choke light goes off. I have taken the center console apart and it looks good. I am running out of ideas on what this can be. anyone have an idea please?

What is the charging system voltage at the battery terminals at both idle and at 2000 rpms', with the headlights on and blower motor at high setting?

 

[tman1029]

What is the charging system voltage at the battery terminals at both idle and at 2000 rpms', with the headlights on and blower motor at high setting?

When I put a voltage meter on it it read 2.5 and when I put the lights and fan on and reved the engine to 2000 rpm it went to 3.9.. Iam assuming the battery
is no good?

 

[Antz81]

When I put a voltage meter on it it read 2.5 and when I put the lights and fan on and reved the engine to 2000 rpm it went to 3.9.. Iam assuming the battery
is no good?

Those voltages are far too low. are you sure it wasn't 12.5 and 13.9?
You can get the battery tested. (it must be fully charged first) that will tell you if there is a problem with the battery. (if they battery is faulty and they replace it, get them to check the new one before you leave)

 

[TimAT]

have an 1981 vette in which the choke light and the battery light stay on after starting. I have replace the battery and the alternator. and they are both still on. I unplug the alternator and both lights go out if I unplug the choke the choke light goes off. I have taken the center console apart and it looks good. I am running out of ideas on what this can be. anyone have an idea please?

I may be too late to the party, but check the fuse for the choke heater. And then the choke heater relay. The alternator plug has 2 wires- a small brown one and a larger red one. The brown wire excites the alternator field to start it charging. And it gets power from the choke heater relay. GM's infinite wisdom I suppose.

 

[Antz81]

I may be too late to the party, but check the fuse for the choke heater. And then the choke heater relay. The alternator plug has 2 wires- a small brown one and a larger red one. The brown wire excites the alternator field to start it charging. And it gets power from the choke heater relay. GM's infinite wisdom I suppose.

Unless my diagrams are wrong it's the gages fuse that provides the excitement voltage. Choke fuse only powers the choke.

 

[Phillip123]

Maybe the alternator is faulty or the diodes in the alternator.

 

[rtman1029]

choke and genator warning light

Maybe the alternator is faulty or the diodes in the alternator.

update I have replaced the choke heater switch relay and the choke light went out, but the battery or the generator warning light is still on. My radio is not working would that have any effect on the light. I also notice that the fan is not working also would that have an effect on the light. The alternator and the battery are good and both have been tested. Is it possible that a ground wire is no good and where is it?... Thanks for your help all,

 

[Antz81]

update I have replaced the choke heater switch relay and the choke light went out, but the battery or the generator warning light is still on. My radio is not working would that have any effect on the light. I also notice that the fan is not working also would that have an effect on the light. The alternator and the battery are good and both have been tested. Is it possible that a ground wire is no good and where is it?... Thanks for your help all,

Radio and fan won't effect the light. The electric fan doesn't start until coolant temperature reaches around 240*f, so it's not unusual to see it stopped (I've never seen mine running)

if you unplug the two wire plug on the alternator does the light go out? If it doesn't then there's a wiring problem. If it does then there's a problem in the alternator

 

[rtman1029]

Radio and fan won't effect the light. The electric fan doesn't start until coolant temperature reaches around 240*f, so it's not unusual to see it stopped (I've never seen mine running)

if you unplug the two wire plug on the alternator does the light go out? If it doesn't then there's a wiring problem. If it does then there's a problem in the alternator

I have unplugged the 2 wire plug and the lights went out. I have had the alternator checked and they said it was good. I guess I am grasping straws trying to find something else is wrong other than the alternator.

 

[bill81vette]

have you checked the alternator with a voltmeter????
it should be putting out 14.2 volts

 

[Antz81]

I have unplugged the 2 wire plug and the lights went out. I have had the alternator checked and they said it was good. I guess I am grasping straws trying to find something else is wrong other than the alternator.

I bought my vette off of an auto-electrician, who said he had rewound the alternator as it failed (I have no reason to doubt him on this), but he failed to notice that the regulator inside it had failed.
Just because someone says something is ok, doesn't mean it is.

as bill says, check the output voltage of the alternator. (Assuming you are the OP, you have done this but the voltage you reported was far too low to be correct. If this is true then you have a new alternator already, which I would assume has a new diode set and regulator)

 

[LLC5]

I have unplugged the 2 wire plug and the lights went out. I have had the alternator checked and they said it was good. I guess I am grasping straws trying to find something else is wrong other than the alternator.

I am assuming that your vehicle has an alternator with a built in regulator, or and integral alternator. If this is true, then you need to start by checking the voltage at the battery at 2000 rpm's, it should be between 13.2-14.5V. If it is, and when you unplug the 2 wire connector at the alternator with the engine off and the battery/alt light goes off in the dash with the key on, then it is more than likely a bad diode trio in the alternator. The diode trio shuts off the alternator/battery light by supplying positive voltage to the bulb in the dash with the engine running, with the engine off and the key on it grounds the bulb and turns the light on. I have a diode trio tester at home to check the circuit, but not many people do and I would guess that probably no auto parts store does either.

 

[kpic]

The term trio means 3 diodes in one assembly.

If one diode is shot your alternator light will come on very dimly. If all 3 are shot; your alternator light will come on very bright.

If one or two of the diodes are shot; the alternator will undercharge. If all 3 are shot; the alternator will not charge at all.

https://www.youtube.com/watch?t=154&v=xgikeXt91vM

 

[LLC5]

The term trio means 3 diodes in one assembly.

If one diode is shot your alternator light will come on very dimly. If all 3 are shot; your alternator light will come on very bright.

If one or two of the diodes are shot; the alternator will undercharge. If all 3 are shot; the alternator will not charge at all.

https://www.youtube.com/watch?t=154&v=xgikeXt91vM

Correct, the diode trio sends a counter voltage to the bulb in the dash to shut the light off, and depending on the voltage sent ( one leg bad, two legs bad, etc) to the bulb it can be dim or bright depending on the counter voltage. The trio also sends voltage to the field circuit, and again depending on the voltage sent, the alternator total output will be affected by the diode trio's condition. The alternator can still function with two legs of the diode trio working, but at a reduced total amperage output.

 

[kpic]

A mechanic once said how can they call it an idiot light when it tests the diodes.

 

[LLC5]

A mechanic once said how can they call it an idiot light when it tests the diodes.

It must mean that any idiot can test a diode. Guess I might be living proof......

 

[kpic]

It must mean that any idiot can test a diode. Guess I might be living proof......

LOL, that was a good one.

All I can add is I've been living proof longer.