So this is what I have.
1967 GT 390 standard interior.
The car is currently not charging. I checked the wires on the alternator and no issues there. The idiot light "AMPS does not come on when key is in the run position but not started. “Oil” idiot light does come on. I checked the “I” terminal on the voltage regulator connector with the key in the same position and there is no 12V.
Any suggestion on where to start on this one?
Thanks, Jim
Is the “AMPS” bulb good? I can’t remember if Fords are wired this way, but some cars will not charge if the idiot light is burned out.
Mike
I plan on checking that tonight or tomorrow. Always fun tearing the dash apart for a bulb. I will check but that seems crazy that they would have a bulb in series to the charging system.
The charging current does not go through the AMPS bulb. With the alternator producing power, it’s stator output energizes the field relay inside the regulator applying 12V to the regulator I terminal. If not, the I terminal has a path to ground inside the regulator which illuminates the AMPS warning light.
Calicat,
So what does all of that mean? I should not see any 12V on the regulator plug terminals with the car not running and the key in the on position? If I ground the “I” terminal with the key in the on position should I see the “AMPS” bulb turn on?
One weird thing I did notice yesterday that made zero sense to me was, when I was messing with the alternator, I took it out with the harness on and while I had the alternator harness unplugged, I put the key in the on position and saw 12V on all three wires of the plug. This makes no sense to me since I traced some of those wires to ground. Just for some background, I’ve been driving this car for years with no charging issues.
Yes, with the regulator unplugged, grounding the I terminal of the wire harness connector with ignition on should illuminate the charging system warning light.
Bad voltage regulator or blown alternator diodes are the most likely problem. Also, make sure the regulator, neg battery cable, and alternator all have good clean grounds to the chassis and engine. Since you already have the alternator out, you can have it tested.
Oh, and to answer your other question, with the regulator unplugged, and ignition off, you should only have 12V on the A (battery) terminal of the harness plug to the regulator. Then with ignition on, you would also get 12V on the I (indicator) terminal through the warning light. There should not be voltage on the S (stator) terminal unless the alternator is grounded and turning with 12V applied to the field. And no voltage on the F (field) because this is supplied to the alternator from the regulator.
You cannot use an LED in the AMPS position. That hole needs a regular bulb.
Yes, the AMPS bulb helps provide the source of current to the alternator field until the regulator field relay closes. So it needs to be a light bulb.
In fact, that might be what tinman was saying about the charge system not working with the bulb burned out. The charge current doesnt go through the bulb, but some of the field current does to kick start the alternator output.
The idiot light is a two wire light, with neither the housing nor base is grounded. One of the two wires on a two wire light is powered via the ignition switch in the ON position with the other wire connects to the “I” terminal on the regulator. This flows through to the field of the alternator, the windings of which finally go to the negative ground.
When the engine is not running and the ignition switch ON, the alternator provides the ground, thus the alternator light glows since the power is provided via the ignition switch. When the engine starts, the alternator stator terminal supplies the positive voltage to the “S” terminal, which closes the field relay in the regulator and now the “I” terminal becomes positive. With both wires going to the plug being positive, the light goes out.
The fact that your ALT light is dimmer than the OIL light when the engine off and the key in the Run position, indicates that the I wiring to/from the voltage regulator is suspect. Disconnect the plug at the regulator, (effectively removing all grounds from the ALT light) and the light should be off. Next, place a jumper wire on the I terminal plug wire and place the other side directly to ground. The light should now glow as bright as the OIL light. If this is the case, remove the regulator and make sure that the bolts and the underneath area of the regultor that contacts the fendor apron is clean. Next, replace the plug at the regulator and recechek the light. If it still does not glow as the OIL light move to the alternator. Make sure the ground wire at the alternator is clean and tight. Recheck the light.
Note, if the ALT light glows dimly when the engine is running, then make sure that the belts are not slipping. Basically when the light glows when the engine is running, this indicates that the voltage at the battery and the voltage produced by the alternator are out of balance, thus causing the light to glow as well. I also recommend removing your alternator and having a shop bench test the alternator which tests the internal diodes, the stator excitation circuit, and the alternator output.
Let me know if you need any additional information
Coach Jack
References:
http://www.mercurycougar.net/forums/archive/index.php/t-15503.html
Thanks Coach Jack, you explained it a lot better than I did. How much of the field excitation current goes through the idiot light vs the ballast resistor across the bulb (assume this is a resistance wire)? In other words, if the bulb is burned out, would the alternator still get some of the field current through the resistor? Or would a burned out bulb keep the alternator from being able to get started charging?
According to my notes, 1 amp total is flowing thru the bulb and a 15 Ohm shunt resistor, 1/4 amp thru the bulb and 3/4 amp thru the resistor. If the bulb burns out, the alternator would still be energized upon startup via the shunt resistor, however not all cars were equipped with the shunt resistor.
Coach Jack
I think I found the culprit. I unplugged the regulator plug and grounded the “I” terminal and the “AMPS” light came on. So that means, from my understanding, everything to the dash is good. I noticed when I put the spare spade I had into the “I” slot of the connector so I could hook up my ground lead, it didn’t feel as tight as it did in the other slots. So I got a tiny screwdriver and worked the internal socket to make it tighter. Also tried to clean it some. Put the connector back on and all is well again. Light comes on with the switch and reading +14 volts on the battery when running.
Now I can play with the Carb Cheater that I just installed.
Thanks everyone for the replies and the charging lesson.
Jim
Gotta love it when the problem can be diagnosed, easily fixed, and we all learn something in the process!