Car is running off the battery, alternator doesn't seem to be charging it.

[d0n_3d]

I can't figure this out. My 86 is running off the battery at 11.5-12.0 volts right now. Yesterday it was running and driving around fine with 13.5-14.0 volts. To make a LONG story short, I swapped alternators and am now running a stock 120 amp. I was running a 200 amp alt that didn't quite work out (see below paragraph). I had the stocker checked out at both advance and autozone and it tested fine. It was putting out over 14.0 volts. So now the alt is back on. I ran a new power wire straight from the alt to the battery. I have a Casper's field fix harness because I did a GNX dash conversion and it can't be that because it was working fine yesterday.

I HAD a 200 amp alt on the car yesterday along with my dual fan setup. I pulled the dual fan system out and put the stock fan back in it. The dual fans suck down way too much juice even for a 200 amp alt. At idle and with the brakes on, I'd be seeing 12.0-11.6 volts (with most accessories on) and when I would go to cruise, the volts were around 13.5 (this is with the fans both running on high). Plus the 200 amp alt needed a smaller belt because of the pulley AND it didn't quite align up with the stock pullies very well (causing noise on the belt). So I decided to take it all off and go back to stock.

So now the car won't charge when running. I checked my fuses and they checked out fine. I took the power wire off the battery going to the alt and tested it with a voltmeter while the car was running and it wasn't showing me anything??? It would show 0.20 volts and then slowly go down to 0. Is this normal? Aren't you supposed to see 14+ volts at the back terminal of the alt when the car is running??? Please help, I'm lost. I never had any problems with my 87 when I did this conversion.

 

[d0n_3d]

I just started and ran the car at idle for 10 minutes (wanted to see if my stock fan was working). It kicked on at about 198 degrees (I forget the exact temps the stock fan kicks on low and high). The car was running at exactly 11.3-11.8 volts the entire time. I put a volt meter at the battery when the car was running and it read 12.04 volts, the same reading at the back of the alternator. I am getting 12+ volts at the field fix harness and 12+ volts at the fuse box under the ECM/Sol fuse. I honestly cannot understand what is going on here. Could the alt still be bad even though autozone and advance both load tested it and it showed fine? I saw the voltmeter at advance and it was showing over 14+ volts under load. Everything in the car works fine other than this. It runs rough at idle and smells really rich because the fuel is not being burned fully (not high enough voltage for ignition to work the best). I'm completely stumped.

 

[DailyDrifter]

Did you plug the wire in going to the alt? On my autometer and Fast my charging system is about 13.8-14volts.

 

[d0n_3d]

its definitely plugged in

 

[PaCemkr86]

does the battery / alt light come on when you turn the key forward?

 

[d0n_3d]

does the battery / alt light come on when you turn the key forward?

I'm not running the factory dash. I don't have any idiot lights in the dash. Electronic speedo, tach, oil, water, volts, and fuel level. I am already running the Casper's field fix. Like I said, it was working fine the other day. Maybe this alt really is bad but I saw it put out 14+ volts at advance when they tested it??? Could the battery be bad??? Maybe its just not holding a charge of more than 12 volts??? But the car ran on straight battery for 10 minutes idling and no sign of voltage drop.

 

[TurboBuRick]

Don, how does the Caspers field fix work? I'm not sure. Is it just a resistor?
Did you try to throw a light bulb inline and go around the field fix. Maybe it took a crap.

 

[PaCemkr86]

Don, how does the Caspers field fix work? I'm not sure. Is it just a resistor?
Did you try to throw a light bulb inline and go around the field fix. Maybe it took a crap.

thats what im thinking

 

[d0n_3d]

Don, how does the Caspers field fix work? I'm not sure. Is it just a resistor?
Did you try to throw a light bulb inline and go around the field fix. Maybe it took a crap.

There is a resistor in the field fix harness but I'm getting 12+ volts from the power terminal on the connector that connects to the back of the alt (terminal F i believe it is for "field"). So the alt is seeing 12+ volts at the f-terminal. I have a new casper's power wire going from alt to battery. What freakin gives! I might try another battery I have just to see if it is that. If not, holy cow I'm clueless.

 

[d0n_3d]

I was thinking...should I check all my grounds like the battery and such? I wonder if this thing is grounding out somewhere. Like I said the car ran for 10 minutes on between 11.3 and 12.0 volts and the voltage never seemed to drop. So the alternator is somewhat charging the battery, I just wonder if some current is getting grounded out somewhere or the battery is bad and can't hold anything over 12. But it can't be the battery cause it holds 12.65 volts when the car is turned off! I hate wiring problems. HATE them.

 

[d0n_3d]

I pulled out the factory battery negative cable and found the terminal that bolts to the cylinder head is coming apart and has dirt, oil, etc in it. It didnt look good. 20+ years and 130K miles will do that! I'm hoping this is what is causing my problem. That would explain why the voltage jumps around everywhere when driving the car and why when I come to a stop, the voltage would drop 1 volt or more and the lights would dim and accessories wouldn't work as good.

Would also explain why the car ran on straight battery for 10 minutes yesterday and the voltage never showed signs of dropping. It is getting charge but some of it is getting grounded out by the bad ground.

Going to Autozone now to get a new cable. Will post results later today.

 

[d0n_3d]

Well it wasn't the negative cable. Still same exact problem. Runs on 11.5 volts. I'm about to burn this car

Gonna call up John at Casper's Monday and find out if he can send me another field fix harness.

 

[GN owner]

http://www.gnttype.org/techarea/images/wiring_images/charging_ckt.jpg

This schematic shows the stock wiring for the field circuit. You should be able to figure out what the field fix actually does by this.

 

[David65]

Don't know where that schematic diagram came from, here's the one I've always went by. Like was said earlier, just take a small lamp (or a resistor, something like a 470 ohm perhaps) and connect it from the L terminal of the 4 pin regulator plug to +12V somewhere. Could even temporarily connect it to the output stud on the alternator, just to try. Just make sure to put something (lamp or resistor) between +12V and the L terminal. Regulator damage will result if you don't...

 

[A2000RICH]

Don't know where that schematic diagram came from, here's the one I've always went by. Like was said earlier, just take a small lamp (or a resistor, something like a 470 ohm perhaps) and connect it from the L terminal of the 4 pin regulator plug to +12V somewhere. Could even temporarily connect it to the output stud on the alternator, just to try. Just make sure to put something (lamp or resistor) between +12V and the L terminal. Regulator damage will result if you don't...

david------its not really necessary to put a lamp or resistor in line with the "L" terminal-------for test purposes it will work fine without it---------don if you want to test your alternator just connect the small wire from the plug directly to the large output post of the alternator and then attach the large wire from that post to the battery + ---------as long as the battery negative and alternator case are grounded (connected) the alt should charge if the engine is running----the alternator cannot begin charging if it is not first connected to the battery because the battery has to supply the current for the rotor to begin the charging cycle------only AFTER the charging cycle is started can you disconnect the battery and still have the alternator continue with an output --------charging would mean the voltage at the large terminal of the alt is more than 12.8 volts--------try this and see what happens--------it appears you have a wiring problem somewhere in your car................RC