Alternator plug wiring issue
Alternator plug wiring issue The day before my T/A broke a lifter, i noticed it was having charging issues and my gauge was bouncing all over. So when i went to pull the motor, i got under the car and was unhooking all the wires and noticed that 3 of the 4 wires had come undone from the cars wiring harness and were just hanging there. They are all the same color (Brown) so i don't know how to tell which one goes where. Can anyone help? 
Last edited by copteezer496; Nov 23, 2009 at 07:47 PM.
brown...never saw brown wires for the alternator.
You talking about the little tiny excitor wire that plugs into the top of the alternator?
Or the big ground wire that bolts to it?
There's only two wires for the alternator. excitor and the cable that branches off to the battery.
The ones you have hanging down...are they going towards the fuse boxes?
.
You talking about the little tiny excitor wire that plugs into the top of the alternator?
Or the big ground wire that bolts to it?
There's only two wires for the alternator. excitor and the cable that branches off to the battery.
The ones you have hanging down...are they going towards the fuse boxes?
.
If the wires are really "all brown" and not just dirty, then someone has changed out the factory plug with a generic parts house replacement. Search the hybrid section for info on your specific car's wiring diagram and go from there.
The wiring connector for the alternator has four connections on it but only one is used, the exciter wire that runs to the PCM. The other three connections aren't used.
Rob (Bad30th)
Rob (Bad30th)
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Verdad Gallardo That's retarded!!! Ok, so what would cause my volts to bounce all over? It maxed out a couple times and every light on my dash came on. I tried putting a new alternator in and that didn't fix it.
Launching!
Joined: Jun 2009
Posts: 268
Likes: 1
THe delphi alternator has several outputs. TACH ICON STATOR ETC. Normally the icon has to be hooked up is your icon WORKING???? Basically the newer alternators dont need any external hookups. I use many DELPHY alternators in the shop with only one wire and they charge. Diesels use the tach output and icon is for dash indication. stator is usually used to controll a relay ETC. If you have an icon and battery at the alternator charge stud it should work. Years ago S10 alternators needed excitation voltage from the icon . But not any more. Check the broken leads for battery or icon voltage ETC or get a print of the system from ALL DATA to see the extra leads and what they do. I will pull a print on monday and see if it neads ext excitation of regulatoe ext BATT. But i dont think it does. JUST FROM MEMORY the print will tell me on monday. Its not retarded you have a simple charging problen its not the end of the world.
Last edited by tom falco; Nov 25, 2009 at 06:38 PM.
Awesome, thanks!! I just think it's kind of dumb that they would put a plug in there with 4 wires and only hook up one of them. Now i just need to figure out which one to hook up.
I'd like to correct a few things that have been posted in this thread...
IN OUR CARS (i.e. the OP's 1998 TransAm), the one wire in the alternator plug is the exciter wire that runs from the alternator (harness) to the PCM. The wire goes in the second spot closest to the driver side (third one from the motor) when it's plugged into the alternator correctly. (Edit - Posted a pic below)...
This wire lets the PCM tell the alternator how much amperage to provide. The factory wire coming from the wiring harness is a very thin dark red wire (when it gets dirty it may look brown). It's easily snapped when removing the alternator, which is why it's somewhat common to see aftermarket replacement wiring harnesses. The aftermarket harnesses are normally generic and come with all four wires, even though you only need the one.
The other three wires in the harness are not needed (the factory plug does not come with them) and can be removed from the aftermarket connector plug, they do not connect to anything in the car.
IN OUR CARS, NONE OF THE WIRES FROM THE ALTERNATOR HAVE ANYTHING TO DO WITH THE DASH, lights or otherwise. The PCM sends the signal to the console/gauges, there is no direct connection from the alternator to the gauges/console.
"Volts bouncing all over" symptoms are usually either due to faulty wiring or a bad voltage regulator (which is inside the alternator on our cars). Swap the alternator and fix the wiring and see if your problems go away.
Rob (Bad30th)
IN OUR CARS (i.e. the OP's 1998 TransAm), the one wire in the alternator plug is the exciter wire that runs from the alternator (harness) to the PCM. The wire goes in the second spot closest to the driver side (third one from the motor) when it's plugged into the alternator correctly. (Edit - Posted a pic below)...
This wire lets the PCM tell the alternator how much amperage to provide. The factory wire coming from the wiring harness is a very thin dark red wire (when it gets dirty it may look brown). It's easily snapped when removing the alternator, which is why it's somewhat common to see aftermarket replacement wiring harnesses. The aftermarket harnesses are normally generic and come with all four wires, even though you only need the one.
The other three wires in the harness are not needed (the factory plug does not come with them) and can be removed from the aftermarket connector plug, they do not connect to anything in the car.
IN OUR CARS, NONE OF THE WIRES FROM THE ALTERNATOR HAVE ANYTHING TO DO WITH THE DASH, lights or otherwise. The PCM sends the signal to the console/gauges, there is no direct connection from the alternator to the gauges/console.
"Volts bouncing all over" symptoms are usually either due to faulty wiring or a bad voltage regulator (which is inside the alternator on our cars). Swap the alternator and fix the wiring and see if your problems go away.
Rob (Bad30th)
Last edited by Bad30th; Dec 7, 2009 at 10:02 AM.
Bad30th is dead on describing how these things work.
I would suggest you peal back the wiring loom tubing to fully expose the ends of the four brown wires you've seen. In all likelihood, only the one that's needed is spliced to the car's harness.
Why does the alternator have a four pin plug? It's cheaper for a manufacturer to make one alternator that fits multiple applications than one for every car. This alternator will fit say twenty different applications each with slightly different needs. That car would simply have the correct number of wires in the plug as needed.
I too broke this wire when hanging the alternator while installing my K-Frame but had enough sticking out of the plug to solder on an extension.
I would suggest you peal back the wiring loom tubing to fully expose the ends of the four brown wires you've seen. In all likelihood, only the one that's needed is spliced to the car's harness.
Why does the alternator have a four pin plug? It's cheaper for a manufacturer to make one alternator that fits multiple applications than one for every car. This alternator will fit say twenty different applications each with slightly different needs. That car would simply have the correct number of wires in the plug as needed.
I too broke this wire when hanging the alternator while installing my K-Frame but had enough sticking out of the plug to solder on an extension.
Launching!
Joined: Jun 2009
Posts: 268
Likes: 1
SO if the ecm controlls the amperage then why do the alternators have a VOLTAGE REGULATOR???? There is a lead on the alt that feeds the ecm on some setups. But the VOLTAGE REGULATOR CONTROLLS THE VOLTAGE IN TURN THIS CONTROLS THE CURRENT. Alternators dont have current regulation only voltage. The ecm as far as i know only receives input from the alt. RPM lamp ETC. The guy changed the alternator and has the same problem???? Your theory is that you dont need any thing plugged into the alt harness only the battery lead. I do tuns of gm diesels and the lamp lead is connected to the alt. So why does he still have a charging problem. I do agree that the alt does not have to controll the icon. Detroit uses a one wire DELPHI 400 amp alt with one wire. The dash processor indicates the icon and not the alt. The alt should charge with one wire and nothing plugged into the harness. Somre alt need excitation from the icon. TOM
I'm not doing to debate how the thing works with you, all I know is that's how my 1999 TransAm is wired and every other 1998 TransAm just like the OP's is wired. 
Are you suggesting he connect the other three wires in the connector up to something ? If so, please do elaborate, heh.
I'm not so much claiming to have a "theory", I'm just telling the OP how the wiring should be and to check it.
Rob (Bad30th)
Are you suggesting he connect the other three wires in the connector up to something ? If so, please do elaborate, heh.
I'm not so much claiming to have a "theory", I'm just telling the OP how the wiring should be and to check it.
Rob (Bad30th)
Just to follow this up with a correction and a pic for good measure, here's a pic of mine - the exciter wire is actually in the second from the outside spot, so I corrected my post above where I thought it was in the second spot from the engine. Mine is an aftermarket plug replacement from NAPA that had white wires on the pigtail.
Cheers,
Rob (Bad30th)
Cheers,
Rob (Bad30th)