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Discussion Starter · #1 · (Edited)
Maybe I am retarded, but I can't get the charging system to work properly on the 87 TR in my signature.

The factory alternator was bad, I purchased an LT1 impala alternator on the recommendation of this board.

I still had no charge, and I discovered that that the small wire that clips into the back of the alternator had no voltage. Again, on the advice of this board I bought a field fix harness from Caspers Electronics.

The car seemed to run OK now, but the battery would die in just a few hours if the car was left sitting. I discovered, again through this board, that the alternator was pulling 12V the entire time. Even with the car off. I took the LT1 alternator back to the store and had it replaced under warranty.

I installed the new alternator, and everything seemed fine. The new alternator did not pull any voltage with the car off. After 2 days, the battery was dead again. I jump started the car and checked for voltage at the alternator with the car running. The big post on the back of the alternator was dead. Zero volts. I removed the alternator and went to the local AutoZone where the alternator tested good, producing the required 14.4 volts or so. I came back to the car and reinstalled the alternator. I put a battery charger on the battery and started the car. Again, the big post on the back of the alternator was dead, no voltage. I pulled the field fix harness off the alternator and tested for Voltage at the 2 of the 4 sockets that contained pins. For simplicities sake we will number the sockets 1 threw 4. Socket number one was the largest of the sockets and was empty. Sockets 2 through 4 are the same size, and socket 2 and 3 contain pins. Socket 2 had 12V and socket 3 was dead.

Looking at the 4 sockets on the on stock connector, only socket 3 contains a pin, so the way I see it pin #3 has to be the pin that the alternator needs to see voltage at in order to charge. I called Casper's and John confirmed that the LT1 alternator did require a different plug. I again started the car and ran a 12V jumper wire to each of the pins in the back of the alternator and checked for voltage. On pin #3 the alternator finally produced the requisite 14V. The field fix harness was suppling power to the wrong pin in order for the alternator to charge. I took the alternator end of the field fix harness apart and swapped sockets 2 and 3. Now, the alternator would see power at pin #3 instead of pin #2. The car ran fine for 2 days.

This morning, the battery was dead again. I started the car with the battery charger again and started to check things. With the large cable not attached to the alternator, the alternator is only producing 11 volts.

The way I understand the system is that the field fix harness is supposed to mimic the voltage drop across the dash bulb, and feed the alternator with some voltage that is less than 12V. My field fix harness, which was wired wrong for my LT1 alternator application, is supplying what ever the battery voltage is to the alternator. If I understand things properly, that will destroy the voltage regulator inside the alternator. To me, that sounds like the problem I am having.

What voltage should the clip on connector provide to the LT1 alternator?

Why doesn't my field fix harness limit it to the proper voltage?

Why did everyone tell me to get the LT1 alternator yet no one mentioned the plug was different?

Can the factory alternator operate with the proper sub 12 Volts applied to pin 2 or 3? The way my field fix harness was assembled, it was supplying 12V to pin #2, where the stock connector was applying voltage to pin #3.

Thanks!
 

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CAPTAIN ELECTRICAL
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with battery and alt all installed and hooked up the voltage at the battery and alt output/charging pole should be the same at all times,running or not.with battery and alt unhooked,the main charging cable should messure zero ohms (measured from both ends).....i think your battery cable to alt is bad or does not have a solid connection.best i can help from my computer...
 

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Discussion Starter · #3 ·
The ohm meter selection on my volt meter doesn't work, but I am seeing roughly a .1 drop in voltage from the alternator to the positive battery post.

Right now I am getting about 14.1 volts at the alternator, and 13.9-14.0 at the battery.
 

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Not a Democrat any more..
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so your alternator is charging and working fine...if battery still goes dead after 2 day and the only thing that draws power from your fuse block is the one fuse we talked about before..then it has to be a..bad connection..cigar lighter maplight or something else in that circuit..still say that it is a vanity mirror and you have not said you have checked all of those...
 

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Discussion Starter · #5 ·
gbsean said:
so your alternator is charging and working fine...
The last alternator was making 14.4 Volts at first as well. After a day or so, it was only making 11 volts, and after 2 days it was only making 4 volts. I took it back and had it replaced under warranty. When I installed the new alternator, I ditched the field fix harness and ran a wire from the connector on top of what appears to be the charcoal canister to post #3 on the alternator. I spliced a bulb socket and a 194 bulb into that wire, hopfully mimicing the voltage drop accross the stock bulb in the dash.

if battery still goes dead after 2 day and the only thing that draws power from your fuse block is the one fuse we talked about before..then it has to be a..bad connection..cigar lighter maplight or something else in that circuit..still say that it is a vanity mirror and you have not said you have checked all of those...
The reason the battery was dead this last time is because the alternator was only charging with 4 volts. With the car off, there is no draw on the battery. I have removed the 'clk' fuse and have verified with a test light and DVM that there is no draw on the battery with the key in the off position. I haven't reinstalled the clk fuse, so there is nothing drawing on the battery when the car is off. If there was a light on, or a short to ground somewhere there would be a small to moderate draw on the battery, and right now there is nothing.

I am concerned about the slow death of the alternators I keep installing. The current one produced 14.5 volts on initial install, and after a 20 minute drive it was down to 14.1. I haven't had a chance to drive the car again, but I anticiapate the alternator voltage dropping slowly over the next few days as the last one did. I'll report back after I drive it some more.

The only difference between this install and the last one is that I have a 194 bulb in the circuit that supplies power to the alternator plug. Does anyone know what kind of voltage the alternator is supposed to receive at that plug?
 

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The 194 is the correct amount of resistance in the line to the alternator.

Voltage should drop as the battery is charged. Should end up somewhere in the 13s after driving a bit. After it sets, is restarted, etc., it should go back into the 14's momentarily, and then drop again.

The alternator has a regulator built in...this varies the charging voltage.
 

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alternator voltage will be different from the back of alternator and the battery due to resistance in the cable...one of the reasons we hot wire our fuel pumps due to the current draw and voltage drop...alternator voltage will vary from time to time...but for it to decrease output over a couple of days has got me wondering if there still is a major current draw that is "burning" out the internal voltage regulator...you say this is your 3rd alternator..another thought is if the battery light and field fix were not working...the alternator would not charge but would bench test ok..but all you are reading is "actual" battery voltage as the battery loses it's charge over a period of time....I have driven 30 miles on the battery alone with my headlights on when my alternator went out...kept my scan tool on the voltage car will still run all the way down to about 6volts....
 

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Discussion Starter · #8 ·
The problem is solved. I wired a 194 bulb inline from a 12V source to the L terminal. Eventually I will test the resistance of the 194 bulb and replace it with the appropriate resistor. I was damaging the voltage regulator in the alternators with the harness from Casper's.

The Casper's harness is designed for an alternator that uses the L and I terminals. The 140 amp LT1 alternator uses L and F terminals.

The Buick alternator will charge when you apply the appropriate voltage to the L terminal, or 12V to the I terminal. The I terminal has an internal resistor to cut the voltage to the correct level to avoid damaging the regualtor. The L terminal gets that resistance from the bulb.

The LT1 alternator uses a terminal labeled as F in place of the Buicks I terminal. The F terminal is for diagnostic purposes and it will not energize the regulator. The harness from Casper's was supplying 12V to the F terminal because the haress was designed to be used on an alternator with the I terminal. When I switched the pins on the harness, that would of solved the problem, except the voltage was not regulated and I damaged the voltage regulator.

It sounds complicated, and was a nightmare to figure out, but in the end it was actually pretty simple.

Cliff notes: The field fix harness will not work with an LT1 alternator.
 

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why did you decide to get a LT1 alternator in the first place? i have a 160 amp and its a standard regal alternator. is the LT1 just a better unit or something else?
thanks
 

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standard turbo regal alternators are 120 amps
 

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If the bulb is in series then I am led to believe it is always lit (i dont have a gn), and therefore the resistance of the bulb must be measured when hot.

Or you could apply 12-13 volts to it, measure the current, and do a little math.

R = V/I
R = 13v/270mA
R = 48.15ohms ~ 47 ohm resistor

Joe
 
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