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Alternator ain't a chargin' 84 glt

JoeLouis

JoeLouis

Active member
Joined
Jul 8, 2023
Location
South Atlanta, GA
So, the 242 began to run out of juice, and I got a jump to get me home. I pulled and had the battery checked, confirmed good. I naively thought it must be the alternator, but I put in a new one, and still no charge....

As with everything else on the car, I wonder what is original and what is TB'd already. This is a photo of the alternator I took off ( probably a better one than the new one, but too late now ) 20241216_114200.jpg

The new alternator had an extra wire ( picture below green dotted line) coming from the black box on the back. Is that a voltage regulator? Where do I hook it up if so?
20250308_150052~2.jpg
Also, I traced the small read wire that I hooked up above and it was connected at a spade terminal that was unhooked below . Does this little guy ( Blue Circle ) connect to the open spade terminal ( Orange Circle )on the starter?

20250405_132511.jpg

Tracing from the spade terminal above it goes to the coil below (Red)

20250405_132518.jpg


Cheers to you for reading, all suggestions welcome.
 
Someone installed a Denso alternator which is a good upgrade for these. The alternator you have as a replacement looks like a clone Bosch. The little black box on the back of it is a noise suppression capacitor and should go to the large B plus wire, the large red wire. You will also need a wire to go to case ground to the alternator mounting bracket. The little red wire has nothing to do with the coil or starter and should not go there. It should go to the engine compartment large gray connector near the back of the engine on the drivers side. That's the warning lamp wire and goes to D plus on the alternator.
 
My 84 glt ate the battery cables. Hell, I've seen a couple dozen do it of all years so far. If that alternator is good, being signaled, and the battery is good, do the right thing and run new cables.

And for the love of god do NOT use those clamp style corrosion magnet battery terminals.
 
Dave, As per usual you are correct. The small red wire was going to the 8 pin connector on the firewall, and I hooked up the black wire (noise suppression capacitor) to the Battery+ (large red wire post), and grounded the case to the block......

Still not charging...

I hooked up the volt meter to the back of the alternator and it's the same as the battery (11.9* volts). Did I get a bad reman. alt.? I'm going to unplug the battery+ from the back of the alternator and then start the car and see if the alternator is putting out anything....
 
JoeLouis said:
Dave, As per usual you are correct. The small red wire was going to the 8 pin connector on the firewall, and I hooked up the black wire (noise suppression capacitor) to the Battery+ (large red wire post), and grounded the case to the block......

Still not charging...

I hooked up the volt meter to the back of the alternator and it's the same as the battery (11.9* volts). Did I get a bad reman. alt.? I'm going to unplug the battery+ from the back of the alternator and then start the car and see if the alternator is putting out anything....
Click to expand...
OK next I would verify the charge light works properly. You can ground the small red wire to the case or to a convenient ground. Turn on the key and it should light. If it doesn't you may have an open circuit or bad bulb. If it does light you verified it works and also tested the case ground if you went to the alternator. With a good charge light circuit I would then say you have a bad new alternator. One other thing is to make sure the small red wire goes to D+ when you connect it to the alternator. Some also have a D- connection which you do not use.
 
Well, looks like the charging light works because it came on when I took the connection from the alternator to the starter off (at the starter). Started the car, and the voltage reads 35+/-! volts coming off the alternator, what in the French toast?... maybe I should plug in the spade connector (blue) that looks like it should plug into the side of the starter(orange)...? I'm confused as usual.

20250405_132511.jpg
 
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35v? That light should not come on when you mess with wires at the starter. It seems like the small red wire is on the wrong terminal or the large red wire is on the wrong terminal. Are you sure the large red is on B+? The small red wire is on D+? The only thing the wiring at the starter has to do with it is the large red wire meets the battery cable there. So you can charge the battery and run the cars electrical system.
 
JoeLouis said:
Well, looks like the charging light works because it came on when I took the connection from the alternator to the starter off (at the starter). Started the car, and the voltage reads 35+/-! volts coming off the alternator, what in the French toast?... maybe I should plug in the spade connector (blue) that looks like it should plug into the side of the starter(orange)...? I'm confused as usual.

View attachment 31934
Click to expand...
Took that wire B+ off at the alternator and the black wire from the noise suppression and the alternator is putting out 16v...cool

When I hook up the little black wire (noise suppressor) it puts out 35v....no bueno

So I just left the little black wire off, hooked it back up and it's still not charging....So 16v is getting to the connection at the starter to the battery but once I hook it up it...voltage at the battery doesn't seem to budge.
 
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dl242gt said:
35v? That light should not come on when you mess with wires at the starter. It seems like the small red wire is on the wrong terminal or the large red wire is on the wrong terminal. Are you sure the large red is on B+? The small red wire is on D+? The only thing the wiring at the starter has to do with it is the large red wire meets the battery cable there. So you can charge the battery and run the cars electrical system.
Click to expand...
Sorry, I could have written that better. I took the alternator B+ wire off where it connected to the battery cable at the starter. That's where I checked the voltage ( at the end of the B+ wire that came from the alternator ) and it read 35v, but after I disconnected that at the alternator and the black wire that was on the same post, now I get 16v. Getting somewhere. The spade connector in the picture was just tempting to plug in....but not the issue.
 
Why would the alternator put out 16V, and then when I hook it up to the battery (at the starter it connects to a post that only has B+ connected) it not charge? The wiring coming off the positive battery post is below. Blue (left) goes to an electric fan, Green (center) goes to the starter, and orange (right) goes to a junction (additional picture) that has 3 red wires out going into the cabin...any ideas appreciated. Ug.


20250412_100430.jpg
20250412_094353.jpg
 
Well the alternator is excited by the small red wire to trigger charging. So that is where to double check. Also make sure that the case ground is good. They can crack and split underneath where it goes to the mount bracket.
 
JoeLouis said:
So, the 242 began to run out of juice, and I got a jump to get me home. I pulled and had the battery checked, confirmed good. I naively thought it must be the alternator, but I put in a new one, and still no charge....

As with everything else on the car, I wonder what is original and what is TB'd already. This is a photo of the alternator I took off ( probably a better one than the new one, but too late now ) View attachment 31848

The new alternator had an extra wire ( picture below green dotted line) coming from the black box on the back. Is that a voltage regulator? Where do I hook it up if so?
View attachment 31849
Also, I traced the small read wire that I hooked up above and it was connected at a spade terminal that was unhooked below . Does this little guy ( Blue Circle ) connect to the open spade terminal ( Orange Circle )on the starter?

View attachment 31851

Tracing from the spade terminal above it goes to the coil below (Red)

View attachment 31853


Cheers to you for reading, all suggestions welcome.
Click to expand...
The lead that goes to the coil and comes from the starter is the start engine boost signal. For starting the starter provides 12v to the coil to make it easier to start. Then when you turn the key to run from cranking the power to the coil is supplied through the ballast resistor.
 
JoeLouis said:
Blue (left) goes to an electric fan, Green (center) goes to the starter, and orange (right) goes to a junction (additional picture) that has 3 red wires out going into the cabin...any ideas appreciated. Ug.

View attachment 31956
View attachment 31957
Click to expand...

To put your mind at ease... the wires coming from the positive battery terminal look normal. As you surmise, the fat wire provides electrons to the starter motor, the blue feeds the fan and it was obviously added external to the terminal nut. That "question mark" junction to the cabin is what feeds the main fuse panel and therefore everything else in the entire car. Note that both are actually molded into the terminal clamp -- many cars use a twin connection of a fat wire and thin wire coming out of the same terminal.

What's unusual is a positive cable on the negative terminal. The color red is a dead giveaway of course, but notice also it has that extra thin wire which is ignored. At the very least, I would wrap that cable in black tape so that it's the correct color to not confuse you later. Or at least wrap a few inches of each end, as a marker. You'll thank me later.
 
Thanks y'all. Your support is invaluable.

So, I put the new alternator back on, and it looked like it was charging....then I drove it and it stopped...more updates, info. and pictures soon.
 
I've had alternators fail like that. They charge when you start up and then after about 20 minutes the charge goes away and you're running on the battery. Drove me crazy when this happened. It was my bro in laws car and it would start up then he would get stranded and need a jump. He would get home and the next time you started the fail cycle would happen again.

when they test them at the stores they aren't hot from driving.
 
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