Alternator question. I need a Lars for electical systems.
Thread Starter
Pro
Joined: Apr 2004
Posts: 687
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From: Atascadero Ca
Alternator question. I need a Lars for electical systems.
I've got the 73 thats still having troubles with the charging system. Alternator is a brand spankin new out of the box 85 amp. I hook it up, belt has tension, everything spins correctly however it's not putting out anything. THe ground wire is bolted to the alternator case, the + is hooked to +, I even switched the 2 little wires back and forth a dozen times. I only get 10 volts out of the alternator, which is exactly how much my battery has in it. Any thoughts?
Also, my connector that has the 2 small wires in it has broken off, which way is it supposed to go on there? black with white stripe (the one that has 12v going to it at all times) should be the pin on the right when looking at the back, correct?
Thanks, Mike
Also, my connector that has the 2 small wires in it has broken off, which way is it supposed to go on there? black with white stripe (the one that has 12v going to it at all times) should be the pin on the right when looking at the back, correct?
Thanks, Mike
Thread Starter
Pro
Joined: Apr 2004
Posts: 687
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From: Atascadero Ca
ok, lets start with something simpler... Could someone take a digital volt meter and tell me the following readings with their motor on and idling...
Ground you black probe to something.
What is the voltage coming out of the alternator B+ (large red) terminal?
What is the voltage coming out of the small terminal, wire on the left while looking from behind?
What is the voltage coming out of the small terminal, wire on the right while looking from behind?
Thanks, Mike
Ground you black probe to something.
What is the voltage coming out of the alternator B+ (large red) terminal?
What is the voltage coming out of the small terminal, wire on the left while looking from behind?
What is the voltage coming out of the small terminal, wire on the right while looking from behind?
Thanks, Mike
Instructor
Joined: Apr 2004
Posts: 235
Likes: 0
From: Mansfield Ohio
If the alt is internally regulated, I believe the wire closest to the (+) terminal should go to the idiot light or gauge. The connector wire farthest from (+) terminal is also connected to (+) battery power in the wiring harness (not sure why they do that instead of just connecting it to the (+) terminal on alternator). If you connect the (+) wire from the plug to the (+) terminal which is connected to the battery, I believe the alt should charge even if the connector wire closest to (+) termial is left disconnected.
C6 the C5 of tomorrow
Joined: Nov 2000
Posts: 6,665
Likes: 2
From: Twin Cities Minnesota
Yep:
The small brown wire is there to excite the altenator. It is a resistance wire on the Vette, a light bulb on cars with an idiot light. It supplies just enough current to get the alt going. Without it the alt will never start charging.
It MUST have resistance or it will burn out the alt!
Too much resistance and it will never start charging.
The bigger wire of the two is the sense wire. It measures the voltage on the horn relay and tells the alt how much current to put out to keep the voltage constant.
When measuring voltage the horn relay is actually a better indicator of alt voltage than the stud on the alt since the horn relay voltage is what the alt measures.
The small brown wire is there to excite the altenator. It is a resistance wire on the Vette, a light bulb on cars with an idiot light. It supplies just enough current to get the alt going. Without it the alt will never start charging.
It MUST have resistance or it will burn out the alt!
Too much resistance and it will never start charging.
The bigger wire of the two is the sense wire. It measures the voltage on the horn relay and tells the alt how much current to put out to keep the voltage constant.
When measuring voltage the horn relay is actually a better indicator of alt voltage than the stud on the alt since the horn relay voltage is what the alt measures.
Originally Posted by mrvette
OK, at the alternator main output stud you will get system voltage, same as battery, damn close anyway....
the wire most clockwise, the black with wh trace goes through the ampmeter on dash to the steady on 12 volt source, same point electrically as the dist block terminal on the horn relay on your drivers side fender liner....so the circuit is, from dist relay, in through firewall connector under brake booster, to amp meter one side, out the other side, back through firewall to the alternator MOST clockwise terminal on the 2 pin connector, sometimes this is red wire IF the connector was changed out in past.....
the other wire is typically brown, and when old the two are easily confused....that goes usually in most cars of this vintage through a lightbulb marked alt/bat/gen on the dash....the other end of the lightbult goes to a SWITCHED HOT on the ignition side....
this lightbulb is sometimes replaced by a resistance wire in our vettes, the ones without any red dash light.....
GENE
the wire most clockwise, the black with wh trace goes through the ampmeter on dash to the steady on 12 volt source, same point electrically as the dist block terminal on the horn relay on your drivers side fender liner....so the circuit is, from dist relay, in through firewall connector under brake booster, to amp meter one side, out the other side, back through firewall to the alternator MOST clockwise terminal on the 2 pin connector, sometimes this is red wire IF the connector was changed out in past.....
the other wire is typically brown, and when old the two are easily confused....that goes usually in most cars of this vintage through a lightbulb marked alt/bat/gen on the dash....the other end of the lightbult goes to a SWITCHED HOT on the ignition side....
this lightbulb is sometimes replaced by a resistance wire in our vettes, the ones without any red dash light.....
GENE
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Originally Posted by 427V8
Yep:
The small brown wire is there to excite the altenator. It is a resistance wire on the Vette, a light bulb on cars with an idiot light. It supplies just enough current to get the alt going. Without it the alt will never start charging.
It MUST have resistance or it will burn out the alt!
Too much resistance and it will never start charging.
The bigger wire of the two is the sense wire. It measures the voltage on the horn relay and tells the alt how much current to put out to keep the voltage constant.
When measuring voltage the horn relay is actually a better indicator of alt voltage than the stud on the alt since the horn relay voltage is what the alt measures.
The small brown wire is there to excite the altenator. It is a resistance wire on the Vette, a light bulb on cars with an idiot light. It supplies just enough current to get the alt going. Without it the alt will never start charging.
It MUST have resistance or it will burn out the alt!
Too much resistance and it will never start charging.
The bigger wire of the two is the sense wire. It measures the voltage on the horn relay and tells the alt how much current to put out to keep the voltage constant.
When measuring voltage the horn relay is actually a better indicator of alt voltage than the stud on the alt since the horn relay voltage is what the alt measures.
Last sentance is not quite correct, IF you have a bad wire from alternator stud to the horn relay.....or not thick enough to carry 100 amps or so without tooooo much voltage drop, and therefore burning up....I use a thick mahuska wire.....
GENE
Melting Slicks
Joined: Mar 2004
Posts: 3,365
Likes: 0
From: Farmers Branch TX
Cruise-In VI Veteran
St. Jude Donor '09
I had this same problem with my 78, the alt. on it was internally regulated and the problem was corrosion on the socket for the idiot light, the light was going off, but was causing too much resistance on one side of the bulb to allow the alt. to charge.
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