Alternator Warning Light or Lamp

[moose425 16]

I have a 1969 GT, with an alternator warning light located next to the oil warning light.  The alternator warning light should be light when the ignition switch is in the accessory position or in the run position with the engine off.  It does not light in either case.  I have checked the bulb and it is OK.  System charges fine at 14.4 volts.  I believe i have an electronic voltage regulator rather than the old electro-mechanical style.  Can anyone tell me what is wrong or what tests I can run?  Thanks so much for any help.

Mark

[Midlife 814]

By any chance have you converted the standard dash to tach dash, along with the associated wiring?  Your voltage regulator plug should have all four pins in use.

 

If not, it could be that the circuit card is bad, the contacts at the dash cluster connector are not making good contact, etc.  My understanding of the alternator indicator lamp is that is should light under the conditions you describe, but I won't swear to that fact. 

[moose425 16]

My car came from the factory with the tachometer in place.  At one time the alternator warning light worked as it was required to (switch in accessory or in on with engine off the light came on).  When I ground the top connector on the four pins on the regulator pig tail the alternator light comes on as it should.  Such tells me I should not have a connector problem somewhere in the ciurcuit.  I can't remember if this problem started when I switched over to the electronic regulator; I don't think it did. Thanks.     

[unilec 57]

So have you changed the alternator? From memory there is a contact in the alternator regulator that supplies one side of the light, should be green with a red stripe wire, the other side of the light is fed from the fuse panel.

[moose425 16]

No, not recently.  Alternator seems to work fine.  Yes, there is a green wire with red stripe.  That feeds one side of the light; with the ignition switch in the accessory position the other side of the light should see ground inside the regulator; thus putting a voltage across the light and lighting it up. Thanks.

[Midlife 814]

No, not recently.  Alternator seems to work fine.  Yes, there is a green wire with red stripe.  That feeds one side of the light; with the ignition switch in the accessory position the other side of the light should see ground inside the regulator; thus putting a voltage across the light and lighting it up. Thanks.

Uhhhh....no.  The two leads in the dash cluster are the green/red wire that goes to the voltage regulator and the other lead is the ACC power line from the ignition switch (1969) or the RUN-only line (1970). For 1970, the lamp will not light with the key in ACC.

[moose425 16]

OK, I can't really go by wire color as my car does not follow the wire colors in the Ford wiring diagram.  I believe I have found the issue.  When the car is started, the current flowing through the bulb flashes the field in the alternator rotor and brings the alternator voltage up to the point where the voltage is applied across both sides of the bulb and the light goes out.  In the event the bulb burns out, in order to flash the alternator rotor Ford wired a resistance in parallel with the bulb.  If the bulb is burnt out, current will flow around the bulb via the resistance wire and flash the field.  With my electronic voltage regulator, the dash light is very dimly light with the switch in the accessory position.  I think my only hope is either to go back to a mechanical regulator, or apply more resistance in parallel with the bulb forcing as much current flow through the bulb as possible.  I guess I will need some concern as to whether or not excessive resistance in parallel with the bulb will prevent the field from flashing if the bulb blows.  I'll have to experiment and see what happens.  I will update my post accordingly.  I wonder if on the 1970 Mustang, Ford went with an electronic regulator and such is why the light does not come on or is very dim.  1970 was about the time transistors where coming into the field of play.  I believe the root problem is the electronic regulator applies more resistance in the circuit downstream of the bulb making it more difficult to establish a ground and light the bulb.  I will try to find my old mechanical regulator and see if it lights the bulb.  I got tired of the old mechanical regulator as it makes the dash lights pulse at idle.        

[moose425 16]

I have solved this problem.  I now have an electronic voltage regulator installed and my dash alt light works perfectly.  It required cutting one wire, splicing into another, and installing a variable resistor from radio shack.  Light works perfectly as it should.  I will draw up a sketch and post it on here soon so others may use my solution.  

[Ed Wiersma 0]

Moose I have same problem Would you tell me which wires you spliced and which Ohm resister you used

[RPM 1,190]

Unfortunately moose hasn't been around for five years.

[Ed Wiersma 0]

Alt light does not come on with key on and engine shut off . Have power to both sides of the idiot light at the cluster. Have power at voltage regulator I terminal , When the i terminal is grounder the light comes on , Makes no difference whether i terminal id plugged in to regulator or unplugged I am wondering what causes this I terminal to have some power Any suggestions

[Midlife 814]

Well, the I terminal should have power with the VR unplugged and the key on ACC for 1969's but lowered voltage due to a resistor wire required to energize the VR if the alternator lamp bulb goes out.  When the VR is unplugged, it will have a full 12V due to no current load. 

The lamp compares the output of the VR (or the ACC-induced power) to RUN-only power when the key is in the RUN position.  I'll bet you'll get the lamp to light up by putting the key in RUN but not running the engine. 

[Ed Wiersma 0]

I Get the following readings at I terminal 

Unplugged from VR  Key Off 0 volts light off  Key Run engine off 12.75 Volts light off Ground I terminal Key run engine off .03 volts light comes on

Plugged into VR Key off 0 volts light off  Key in run engine off 11.99 volts light off Ground  I terminal Key run engine off .03 volts light comes on

Car running light does not come on Alternator charging  14.25 at battery

My thoughts are in order for the light to come on with key in run and engine off the voltage on I terminal should be  reduced  when plugged in the VR Would it be a faulty VR or an alternator Problem?  or anyone Know how to test this

[Mach1 Driver 560]

I suggest you read this for a better understanding of the circuit: