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i have a 73 camaro with 95LT1 and M6 tranny ... using LT1 alternator and factory (79 camaro) wiring harness... car runs great .. when driving and hitting hard bumps (damn potholes in PA) the voltmeter will drop from 14 to 12 volts and then go back to 14 .. this happens at each hard bump. when driving at night with lights on, lights really dim on guages and also in headlights then brighten back up when guage goes to 14 v. thought it was a ground .. checked all and they are tight. stud on back of the alt was loose .. had this tightened at alternator rebuilder. still does not work. Is it possible that something is damaged in the alternator causing this? or Battery? i thought if this was a short somewhere, i would have blown a fuse by now.

any ideas???? i am not the best at troubleshooting electrical.

thanks in advance.

Brad
 

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Guessing that the alternator is turning off when you hit a bump. If it's running you will have around 14.5 volts out the large terminal. When it's off you start seeing only the battery 12 volts.
I can't tell if it's internal or external to the alternator. However the alternator is fairly self-contained. If it stays off long enough to get the hood open try this.
On the alternator there is a connector with 2 wires. (No schematic so guessing on colors). The red wire comes from the connector and is tied to the large stud on the alternator rear. The other wire (black? brown?) runs back into the harness. It's this wire you are interested in.
While the alternator is acting up, use a probe and a jumper wire. Touch the probe to the black wire crimp joint in the alternator connector. Short this probe/jumper to the large terminal on the alternator rear. See if that starts the alternator. If it does there's a problem with that black wire. If the alternator doesn't start, there's a problem with the alternator.
 

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I would check the wire like John_Muha described. Even if you're not the best at trouble shooting electrical, I would pick up a basic meter to use on the car or at the house as they are not always needed but they do come in handy now and then.
Just to add what John_Muha said, if the alternator does have a small 2 wire plug on the back outside edge of the alternator, have the car running and when the gauge reads hi at 14 volts, then unplug the 2 wire plug on the alternator and this should make the alternator go dead and not be charging and see if the voltage goes down to the lower value you had when you hit a bump. If it does and the alternator is still under warranty, I would maybe try swap that first. If it still acts up then I would also think that the 12volt ignition wire in that 2 wire plug is going dead now and then after you hit a bump.
I remember helping another person on this site with an ignition switch problem and even the "new" ignition switch after a few uses went bad and I told him if it acts up again to try a different source as they may have a run of bad ones.
Electrical problems can be a pain, but keep track of what you are doing and it can be corrected.
I also do not know what wire in the 2 wire plug does what but one does go to an ignition 12v source and I think the other goes to the "GEN" light in the dash but you may want to get a wiring diagram to help out.
Jim/Saint Louis
 

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Discussion Starter #4
thanks for the great info, guys... i have replaced all the factory guages in the car with autometer and no longer have any of the idiot lights as i used a stainless guage panel instead... is there something in the alternator that could be cracked, etc. causing it to stop charging for that second after i hit a bump? unfortunately the problem is not there when the car idles or even is driving on smooth roads. i will look into the test you both advised ... i remember seeing the plastic plug on the alt, not sure where the wires go though ..

i will try to do as you suggested above ... any other ideas? i had the alt shop bench test the unit and it was ok, which makes sense... the large terminal (stud) on the rear was loose .. they disassembled the unit and tightened it.. they though this was the problem .. i re installed it, but still is not right. what is inside an alternator that could cause this?

Brad
 

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Brad,
I had a problem years ago when I had no gauges and just the idiot light. Once in a while the "GEN" light would be on dim, sometime bright and then off. Who knows what the battery voltage was when it happened but I replaced the regulator inside and it worked just fine for a few months and then started doing the same thing. Again, I replaced the regulator and then again a few months later it acted up. I said enough and took the thing apart and after some searching it turned out to be a crimped on connector inside that has 2 or 3 wires going into the connector off of the windings on the case of the alternator and the ring terminal went to a stud on the regulator. Turned out to be a corroded ring terminal and by me moving it around with the regulator replacement it would make contact on all of the wires. After a while they would corrode and sometimes make connection. I took the ring terminal off, cleaned the wire ends, put a new end on it and soldered it and it never happened again.
It's a true story but it shows some things I had to go through on mine.
You did a good thing putting in a volt gauge and it is a ton better than the old "Idiot" lights.
I wonder too if you could take a rubber mallet and smack the alternator case and see what happens (not too hard).
Jim/Saint Louis
 

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Originally posted by SOA-Nova:

I also do not know what wire in the 2 wire plug does what but one does go to an ignition 12v source and I think the other goes to the "GEN" light in the dash but you may want to get a wiring diagram to help out.
Jim/Saint Louis
I read this as him having a later SI style or internally regulated alternator. If it is, one lead doesn't go a switched 12 volt source. That lead would be the voltage sense line and is tied to unswitched battery voltage. GM usually ties it to the large terminal on the rear. Works pretty good if the car doesn't have large power items added to it.
The other lead does go back to the GEN light. I agree, schematics are a great tool. I can't work well without one. Usually just stumble around.
 

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Thanks for the info, John. Now I can take the voltage sense wire and connect it to the trunk mounted battery to monitor charging voltage and it will adjust itself, i.e., correct for wire losses, 4/0 AWG, etc.

Monitoring voltage at the "end" of the load is alot better regulation than at the "source."
 

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Originally posted by Everett#2390:
Thanks for the info, John. Now I can take the voltage sense wire and connect it to the trunk mounted battery to monitor charging voltage and it will adjust itself, i.e., correct for wire losses, 4/0 AWG, etc.

Monitoring voltage at the "end" of the load is alot better regulation than at the "source."
Yes, but remember one thing. If you run a large 4/0 wire from the rear to the front, agree that there is resistance in that wire. However moving a small gage sense line all the way to the rear defeats the purpose. The drop in the small sense wire is greater than the drop in the 4/0 feed wire. May force the regulator to run higher than it should.
Might be better to just move it to the starter or a junction block. Take some readings to see if voltage is low somewhere in the circuit and maybe try regulating that point.
 

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I have 4/0 cable. You may be correct in suggesting at starter, but, I'll try a 12 AWG wire back for sensing, there is minimal current, its just voltage "detection."
 
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