Do we have any electrical system guru’s on here?

[767Jockey]

Of all the different areas of working on cars, electrical is by far my weakest, and number 2 on the list isn’t even close. Electrical is voodoo science to me. I know very little about it and I understand theory and troubleshooting even less.

That said, I just switched over to a Ford 3G alternator from the original 60 amp unit from the 60’s. The original unit had been converted to a one wire system a while back. It stopped working so I went to a modern 130 amp Ford 3G. I bought the alternator brand new, it’s a ACDelco Gold unit. The one I am using is from a 1996 Mustang with a 6 cylinder. After swapping the pulley to my old V belt and re-clocking the back putting the terminal locations in the proper position in relation to the mounting ears, it’s a direct bolt on, and it fits like a glove. The hookup is stone simple. I ran a heavy 6ga wire from the main output terminal on the alternator to the battery terminal on the starter solenoid. There are two plugs on the back of the alternator. The larger one has 3 wires coming out of it, the smaller is one single white wire. The directions I followed said to connect the white wire from the small plug to the white wire from the triple terminal. I did that, soldered and heat shrink wrapped it. There is a yellow wire that comes out of the triple plug, that goes back to the battery terminal on the solenoid as well. The last connection is the green wire from the triple plug. I ran that to the IGN terminal on the ignition switch. All connectins are soldered and covered with heat shrink sleeves. The drawing below is what I folloeed for directions. They're all good coonnections. I started he car and perfecto! I had a solid 13.8 volts…..until I didn’t.

Today I started the car and it’s not charging. I noticed the voltmeter in the car was low, and with the car running I measured back at the battery terminals with a VOM and got only 11.8 - 11.9 volts. All the connections outlined above were checked and re-checked. They’re all good. I took off the two main grounds on the car, cleaned and re-grounded them. All good. I took the alternator to two different auto parts stores to spin up in their machine to check it. Both said it checked out just fine. The fan belt is plenty tight. I checked the mega fuse in the main charging line off the alternator. It's intact and fine.

At the same time I also have a problem with my electric fuel pump. It’s struggling to run, binding, surging, sputtering and moaning. It’s shot. I have a new fuel pump arriving here in a couple of days. Could the draw on this bad pump be so high that it’s messing up the charging system somehow? If it matters, my car has a Ron Francis Factory 5 Cobra harness. It’s not a Factory 5 car (it’s a Contemporary) but the harness worked out well. The fuel pump relay is on the fuse panel. Could something wonky be going on with the fuel pump relay to cause this charging issue? I know I’m grasping at straws but how all his works together is a mystery to me.

Also, I have read that some guys attach the wire that runs from the alternator to the ignition switch to the ACC terminal on the ignition switch instead of the IGN terminal as I have it hooked up now. Could this be an issue? It did work before like this however. Maybe the IGN terminal isn’t supplying the proper signal to the alternator to wake up and do its thing?

Maybe the alternator stops charging when it gets hot? I don’t know how you’d check that other than letting it cool off and see if it works again. I can’t try that right now, it’s past 11PM here and this thing is LOUD.

A friend of mine is trying to assist long distance but I hate to keep bothering him (sorry Jon!) If anyone has any ideas on where to look further I would greatly appreciate the input. Thanks!

[strictlypersonl]

"The last connection is the green wire from the triple plug. I ran that to the IGN terminal on the ignition switch."

Follow the instructions labeled "Cars with Gen or Alt warning lamp." You may need a light or resistor in the circuit.

[767Jockey]

I had a red light in the dash that was on all the time. It was super annoying, I disconnected it. I wonder if that was the issue. I'd rather have the resistor. They have 560 ohm resistors on Amazon. Would the 2 watt resistors be durable enough for this application? I have no idea. I'd really rather not have to look at that bright red light all the time if I don't have to. Do I need to reconnect the light AND a resistor, or will just the resistor suffice?

[fastpace]

Originally Posted by 767Jockey

I had a red light in the dash that was on all the time. It was super annoying, I disconnected it. I wonder if that was the issue. I'd rather have the resistor. They have 560 ohm resistors on Amazon. Would the 2 watt resistors be durable enough for this application? I have no idea. I'd really rather not have to look at that bright red light all the time if I don't have to. Do I need to reconnect the light AND a resistor, or will just the resistor suffice?

2 watt should be more than enough, that 160mA at 12V. You can have just a 560 ohm resistor, you don't need the light. If you had the light and you've since taken it out then that is definitely the source of your issue.

[patrickt]

Originally Posted by 767Jockey

I had a red light in the dash that was on all the time. It was super annoying, I disconnected it. I wonder if that was the issue.

Good thing it wasn't the oil pressure light.

[Morris]

On a charge light on the dash.....one side goes to the battery via the ignition switch (12 volts) which is 12 volts.....the other side of the lamp .....goes to the alternator which is close to the same on both sides of the lamp putting out 13.5-14.5 volts....which means the lamp will not light because the potential is the same on both sides of the lamp......if the voltage from the battery or the alternator starts to fail....then the difference in potential gets larger and the lamp starts to light.....the brightness of the light depends on the amount of voltage difference between the two sides of the lamp.....it at least warns you that something is not working properly in your electrical supply system....I doubt that the fuel pump had any effect on the Battery/Alternator lamp or supply.

[767Jockey]

Originally Posted by patrickt

Good thing it wasn't the oil pressure light.

Nah, I knew it was a charge light. However, rather than going on when something goes bad as most warning lights do, it was designed to stay on and then go out when there was a problem. It's annoying.

[767Jockey]

Originally Posted by Morris

On a charge light on the dash.....one side goes to the battery via the ignition switch (12 volts) which is 12 volts.....the other side of the lamp .....goes to the alternator which is close to the same on both sides of the lamp putting out 13.5-14.5 volts....which means the lamp will not light because the potential is the same on both sides of the lamp......if the voltage from the battery or the alternator starts to fail....then the difference in potential gets larger and the lamp starts to light.....the brightness of the light depends on the amount of voltage difference between the two sides of the lamp.....it at least warns you that something is not working properly in your electrical supply system....I doubt that the fuel pump had any effect on the Battery/Alternator lamp or supply.

Morris, this darned thing stayed on all the time.

[patrickt]

Originally Posted by 767Jockey

Morris, this darned thing stayed on all the time.

I think Morris confused you. A charging system that actually uses the idiot light does so by running current through the filament of the bulb to the voltage regulator. When it does this, it "excites" the VR to begin charging the system (assuming the alternator is working). The lead from the VR to the bulb is a ground circuit before the exciting takes place. Once the exciting takes place, it is a positive feed. So, when everything is running properly the bulb has a positive feed to both sides of it, so it doesn't light. BUT, if either side is noticeably "less positive" than the other, then the light will burn dimly. If either side is really negative, then the bulb will burn brightly. Sometimes the filament of the bulb does not have the proper resistance so you add a resistor in parallel. Now, here's your quiz in order to get an honorary Club Cobra EE degree: How do you measure the resistance of a bulb's filament when it always shows zero ohms when you measure it with your VOM?

[Dominik]

I am also pretty certain that you cannot use a LED pilot light for above reasons. The resistance would be too low.

[strictlypersonl]

Originally Posted by Dominik

I am also pretty certain that you cannot use a LED pilot light for above reasons. The resistance would be too low.

I think you mean "high"...

[spdbrake]

I switched all my dash lights to LED last year.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Red=alt, Blue=hi-beam,Amber=Fan,Green=Turn
I used the 24vdc version as I don't like blindingly bright caution lights. These can easily be seen during the daytime as well.

Had to add a Resistor as the LED did not have enough resistance to trip the alternator on and also turn off the light.
https://www.amazon.com/s?k=Twidec%2F...f=nb_sb_noss_2

Back to the OP original question. The alternator may have set too long causing the original problem. https://www.engineersedge.com/motors...d_flashing.htm

[krausewich]

Originally Posted by Morris

On a charge light on the dash.....one side goes to the battery via the ignition switch (12 volts) which is 12 volts.....the other side of the lamp .....goes to the alternator which is close to the same on both sides of the lamp putting out 13.5-14.5 volts....which means the lamp will not light because the potential is the same on both sides of the lamp......if the voltage from the battery or the alternator starts to fail....then the difference in potential gets larger and the lamp starts to light.....the brightness of the light depends on the amount of voltage difference between the two sides of the lamp.....it at least warns you that something is not working properly in your electrical supply system....I doubt that the fuel pump had any effect on the Battery/Alternator lamp or supply.

Morris.. So your saying there is some truth to when the Ol' lady says "I thought the light would get brighter if it were serious?!"

I will never admit to this...

[Blas]

The red light on the dash should turn on with the ignition key in the on position. Once the motor is running and the key is back in the on position (from the crank position), assuming the engines idle RPM’s are sufficient, the red light should go out. There are a trio of diodes inside the alternator. Your alternator is making AC current, and it is being converted to DC current. If any of the diodes are damaged or are beginning to fail, the red light will begin to glow a bit, and as the diode(s) continue to fail, the red light will get brighter and brighter. Most single wire alternators are not designed to have the charging light functional. There are a few exceptions out there and there is an aftermarket circuit that can be added which will make the red light functional again with a single wire alternator. Lots of people put way too high output alternators in cars with wiring not designed for large amperage units.
Blas

[incoming]

@Patrickt, get a better meter if you need a specific number.

[767Jockey]

I've been told that I can eliminate the red light and just put a 560 ohm resisitor in the line that goes to the ignition switch. If that's true and that'll work, that's fine with me. I have a functioning voltmeter and no use at all for the red light as a warning. Will the 560 ohm resistor in the line to the ignition switch without the red light being hooked up work as a way to excite the alternator into action?

[patrickt]

Originally Posted by 767Jockey

Will the 560 ohm resistor ... work as a way to excite the alternator into action?

It all depends on what you're wearing at the time.

[incoming]

Or how short the passengers skirt is

[fastpace]

Originally Posted by 767Jockey

I've been told that I can eliminate the red light and just put a 560 ohm resisitor in the line that goes to the ignition switch. If that's true and that'll work, that's fine with me. I have a functioning voltmeter and no use at all for the red light as a warning. Will the 560 ohm resistor in the line to the ignition switch without the red light being hooked up work as a way to excite the alternator into action?

Yes you should follow the wiring information you posted under "Cars with 5 gauge cluster" then. So the Lt Grn/Reg wire off the "I" ignition terminal should go through a 560 ohm resistor to a switched power source that is powered at both the start and run positions of the ignition.

[patrickt]

Originally Posted by fastpace

...that is powered at both the start and run positions of the ignition.

Most charging lamp feeds to the VR come off the ACC circuit of the ignition switch and not the START or IGNITION circuits of the switch. The reason is that you don't want the feed to the lamp back-feeding to the starter solenoid. If you do that, you'll know very quickly. The easy way to tell on your particular Cobra and wiring system is to just pull your coil wire so the engine won't start, turn the ignition ON and the charging lamp comes on, now crank the engine and see if the charging lamp goes out. If it does, then the feed to it is coming from the ACC circuit(s) of the ignition switch which gets cut out when cranking. Another way to check is to just pull the wire off the starter solenoid and try and start the car. Of course it won't crank, but watch your charging lamp and if it goes out then you know it's fed from the ACC pole of the switch which is getting cut out. Now, every ignition switch in the world doesn't cut the ACC circuit out while cranking, but you get the idea.