Hi! Welcome from Texas! With the car running, pull the battery cable and see if it dies. If so, it's definitelynot charging. I'd go to a place that can check the charging component while on the car. Could be a bad ground to your voltage regulator.
You might try a Sears auto if one is near by.
I'm pretty amateur at working on my car. So I wanted to clarify a couple things.
By "pull the battery cable", you mean to disconnect the positive wire from the battery itself?
All of the parts were on the car when I had it checked at Advance Auto.
How does the voltage regulator ground? Or how can I check that?
I recently tried to install one of those LED instrument panel kits from Mustang Project and they didn't work. They told me that I probably had a bad ground.
I have no idea if that is helpful or related.
Yes. With engine running and all accessories off, disconnect the positive cable from the battery.
Engine should still run. If not, alternator isn't charging at all.
Let's start with that. Do you have a test light or a voltage meter?
The voltage regulator grounds with the 2 bolts to the fender apron.
I would not do that test where you disconnect the battery with the car running. Im not convinced that will prove anything and could do some damage to the charging system.
Buy, borrow, beg, or steal (kidding) a voltmeter. Check the voltage at the battery with the engine off and with the engine running.
Off should = about 13-13.5VDC
Running should = about 13.5 -14VDC
Important thing is that running should be about 1 - 1.5VDC higher than off.
The alternator light in the dashboard is actually controlled by a relay inside the fender mounted voltage regulator (VR). When the the alternator output reaches a certain voltage the relay in the VR closes shutting off the light. Your alternator could have good output but a failed VR would allow the light to stay on. Im not saying that is what is going on but it is a possible scenario. Do the voltmeter test and report back.
I would not do that test where you disconnect the battery with the car running. Im not convinced that will prove anything and could do some damage to the charging system.
I've been around cars over 40 years and this test is older than I am. Was taught this by a local Ford dealership mechanic over 30 years ago. the point of it is the alternator should be charging slightly and provide enough current to maintain the coil powering the engine. It will in no way damage the electrical system, worst it will do is the engine will die. This is why you only disconnect 1 cable. There's also another method of jumping 2 wires of the voltage regulator connector to force the alternator into maximum charge mode to validate it's current output, but you only do this for a very short time as it could overheat the alternator.
These are basic methods of field testing the older charging systems when a voltmeter or test light isn't readily available.
You might stop by a Harbor Freight and pick up one of their little cheapo volt meters. They aren't much, but will tell you if the system is providing a charge or not. At 1500 rpm, system voltage shoud be above 13.8 volts measured at the battery terminals.
I'll get one and try it out.
I'll let you know the results.
I also forgot to mention that I have the printout from the test I had done at the auto store. Don't know if that is helpful.
Thanks for your help.
Post up a copy of it. Quite possible it has the answer and the tech didn't know it.
Does the light stay lit all of the time? Is it lit with key on, engine off ?
Does it turn off if you rev the engine up to 1500-2000 rpm? Does the light flicker at all?
I've been around cars over 40 years and this test is older than I am. Was taught this by a local Ford dealership mechanic over 30 years ago. the point of it is the alternator should be charging slightly and provide enough current to maintain the coil powering the engine. It will in no way damage the electrical system, worst it will do is the engine will die. This is why you only disconnect 1 cable. There's also another method of jumping 2 wires of the voltage regulator connector to force the alternator into maximum charge mode to validate it's current output, but you only do this for a very short time as it could overheat the alternator.
These are basic methods of field testing the older charging systems when a voltmeter or test light isn't readily available.
You might stop by a Harbor Freight and pick up one of their little cheapo volt meters. They aren't much, but will tell you if the system is providing a charge or not. At 1500 rpm, system voltage shoud be above 13.8 volts measured at the battery terminals.
Sorry, you are completely incorrect. This test was fine when used on cars with GENERATORS but not alternators. The possible current spike when disconnecting the ground cable can damage the diodes in the alternators rectifier bridge, the electronics that turn the AC voltage into DC. If your charging system has passed testing then look for other causes of the light being on. To do so, one should understand the circuit for the ALT lamp, it's a series circuit with the lamp in the middle, one end connected to the IGN "ON" feed and the other to the "I" terminal on the voltage regulator. I'd check the regulator plug to make sure the terminal ends are clean and properly seated and that the regulator is properly grounded. Other things to check would be the regulator's condensor and the ignition switch.
Post up a copy of it. Quite possible it has the answer and the tech didn't know it.
Does the light stay lit all of the time? Is it lit with key on, engine off ?
Does it turn off if you rev the engine up to 1500-2000 rpm? Does the light flicker at all?
Sorry, you are completely incorrect. This test was fine when used on cars with GENERATORS but not alternators. The possible current spike when disconnecting the ground cable can damage the diodes in the alternators rectifier bridge, the electronics that turn the AC voltage into DC. If your charging system has passed testing then look for other causes of the light being on. To do so, one should understand the circuit for the ALT lamp, it's a series circuit with the lamp in the middle, one end connected to the IGN "ON" feed and the other to the "I" terminal on the voltage regulator. I'd check the regulator plug to make sure the terminal ends are clean and properly seated and that the regulator is properly grounded. Other things to check would be the regulator's condensor and the ignition switch.
I was just getting ready to do this test, but I guess it seems I should not. I don't want to even risk damaging my new parts. I just can't afford to replace them again.
I am planning on getting a voltmeter, if that is the safer way to test these things.
I'll check the plug on the regulator. And by properly grounded, it just needs to be bolted to the side of the car to be grounded, right?
"And by properly grounded, it just needs to be bolted to the side of the car to be grounded, right?"
Make sure that whatever chassis ground point you use is paint free, rust free, dirt free, in other words a good clean connection. For example, if the mounting hole for the ground wire has just been treated to a fresh cost of paint, how is the electricity going to get to ground?
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*67 Vintage Burgundy 390GTA with most of the bells and whistles*
Perhaps a peruse of the manual written by the same people who designed and built the charging system on your vehicle might prove enlightening. Here's a link to a .pdf file of the Autolite manual published in 1966.
I was just getting ready to do this test, but I guess it seems I should not. I don't want to even risk damaging my new parts. I just can't afford to replace them again.
I am planning on getting a voltmeter, if that is the safer way to test these things.
I'll check the plug on the regulator. And by properly grounded, it just needs to be bolted to the side of the car to be grounded, right?
Good idea. Yes, by properly grounded either a separate ground wire or a bare metal connection between the regulator housing, chassis and retaining screws. Silicone dielectric grease can be used to protect the connection.
The proper test procedure, when using a voltmeter, it to connect the voltmeter to the battery, start the engine, turn the headlamps on and increase the idle speed to approximately 1,500 rpm. Check the voltage. You should have at least 13.5V. If so, note the ALT lamp. Is it ON? If it's ON dimly, have the rectifier bridge in the alternator tested. If it's on brightly, check the indicator lamp circuit for short or high resistance. If voltage is below 13.5V, stop the engine and unplug the regulator. Start the engine and connect a jumper wire across the A+ and F terminals of the plug for no longer than 10 seconds within a minutes time to avoid overheating the alternator. You should read at least 13.5V and optimally closer to 14.5V. If you only read battery voltage, check the alternator wiring and if correct, replace the alternator. If you get the voltage replace the regulator.
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1973 Mustang Alt Light Staying On
