Electrical I need help with 3G alternator upgrade problem

project_88LX

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Nov 1, 2000
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Oh man, I am normally good at this stuff but sometimes I make a mistake..

I was working on the 91 and decided to do the 3G alternator swap while I was at it since I have the parts on hand. I cut the green and yellow wires and they dropped and hit the alternator body. I forgot to disconnect the battery.... Yes I know.


The started solenoid made a funky noise and there was a little bit of smoke. I disconnected it at that point and got everything done. It starts right up and runs well BUT the volt gauge is not working now or at least showing low near the bottom and it should be at the top. I checked voltage at idle and it's only charging 12.10 volts.


I cut the 2 black wires and tied them together and crimped a ring terminal and soldered and put that on the post on back of alternator.
I also ran a 4ga wire from that little post over to the large left lug of solenoid and installed a 175 amp fuse. The car starts and runs but the gauge is only showing 12 volts still.


I got a new alternator today to make sure and it's putting out the same voltage.


Help please.
 
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ReefBlueGT

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Oct 4, 2018
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I was working on the 91 and decided to do the 3G alternator swap while I was at it since I have the parts on hand. I cut the green and yellow wires and they dropped and hit the alternator body. I forgot to disconnect the battery.... Yes I know.


The started solenoid made a funky noise and there was a little bit of smoke. I disconnected it at that point and got everything done. It starts right up and runs well BUT the volt gauge is not working now or at least showing low near the bottom and it should be at the top. I checked voltage at idle and it's only charging 12.10 volts.


I cut the 2 black wires and tied them together and crimped a ring terminal and soldered and put that on the post on back of alternator.
I also ran a 4ga wire from that little post over to the large left lug of solenoid and installed a 175 amp fuse. The car starts and runs but the gauge is only showing 12 volts still.


I got a new alternator today to make sure and it's putting out the same voltage.


Help please.

Do a search for the 3G alternator swap and you'll find some good schematics and more technical explanations if you're so inclined -- but long story short, do NOT connect anything to the alternator post except the new 4ga wire with the inline fuse. The other end goes back to the solenoid as you indicated. If you connect the original wires with a new ring terminal in addition to the new 4ga, you'll be drawing excess voltage from the alternator that the regulator won't keep up with. I did that before reading up on it more thoroughly and the fusible link on the original wiring fried and I had to replace it. Luckily it didn't start a fire, which is what the fusible link is there to prevent. I'm not convinced of the need to add a corresponding 4ga black wire for the ground to circle back to the chassis from the engine block - I did add one but noticed no difference whatsoever in charging or other performance. And there is already a 4ga from the block to the negative battery terminal. But that's just my opinion/experience. And won't harm anything if you do add it.

If the car is not charging, the battery lamp in the cluster should light - is it on? If it is missing, make sure to replace it, as that's part of the charging circuit too and can't be left open. Also, be wary of relying on the voltmeter in the cluster - the tick marks actually go 8-10-12-13-14-15-16. If you're counting that third tick as 11 and the fourth as 12, you're actually reading one volt short of what it may be. Mine usually floats somewhere between 13-14 (4th-5th tick, near the center of the gauge spread). Mine will get down under 13 only with lights and/or AC on. In any case, verify with a voltage meter as outlined in the schematic and testing post you'll find in your search.

Side note, it's also possible to fry and short the voltage regulator on the alternator; mine was behaving erratically after I fixed the incorrect install and eventually went out. Symptoms were overcharging (slight battery leakage), flickering voltage to lights, etc. And then when I got a replacement and put it in, I neglected to pull out the pin retaining the brushes in the regulator during the install. It immediately shorted when I reconnected the battery, and had to get another regulator and do it right. All a good reminder, as you know, to be overly cautious and thorough when working on the electrical.