Alternator Short?
Posting Guru
Joined: Sep 2012
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I suspect that it's a charge indicator or current gauge. If so, it has a wire (yellow?) that passes through a metal loop on the back of it. That wire should carry the charging/discharging current to and from the battery and then it will make the gauge read properly. Look here:
http://www.clubfte.com/users/earl/Re...ing%20Diagrams
http://www.clubfte.com/users/earl/Re...ing%20Diagrams
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Freshman User
Joined: Jan 2005
Posts: 48
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From: Brentwood, TN
Oh boy. Ignore the post above and thanks for being patient with me guys. As you can tell electrical is not my strong suite.
I think I hooked it up right. + terminal on alternator to + battery; - terminal on alternator to engine ground (where my - battery cable connects); Post #2 (red wire) is attached to + terminal on alternator; Post #1 (white wire) is now connected to the ign post on the key switch (post that only is hot when key is turned to the right to start the truck).
Results? It now indicates a short with or without the plug in the top of the alternator (just attaching the negative battery cable there is a spark); my volt meter on the dash is reading about 13.5 volt output; and when I turn the key to kill the engine the truck stays running!!!
Help???
I'm thinking maybe there is a short in the alternator. I can take it to Advance Auto Parts and they said they can check it.
Thoughts?
I think I hooked it up right. + terminal on alternator to + battery; - terminal on alternator to engine ground (where my - battery cable connects); Post #2 (red wire) is attached to + terminal on alternator; Post #1 (white wire) is now connected to the ign post on the key switch (post that only is hot when key is turned to the right to start the truck).
Results? It now indicates a short with or without the plug in the top of the alternator (just attaching the negative battery cable there is a spark); my volt meter on the dash is reading about 13.5 volt output; and when I turn the key to kill the engine the truck stays running!!!
Help???
I'm thinking maybe there is a short in the alternator. I can take it to Advance Auto Parts and they said they can check it.
Thoughts?
Fleet Owner
Joined: Jul 2004
Posts: 27,290
Likes: 1,055
From: NM
It seems that you are getting voltage to the IGN circuit from somewhere besides the switch; could be a bad ignition switch too. How did you shut the engine down?
If there was a short somewhere, you'd see smoke.
If there was a short somewhere, you'd see smoke.
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Freshman User
Joined: Jan 2005
Posts: 48
Likes: 0
From: Brentwood, TN
It's a three prong ign switch. One post is batt (always hot), one post is hot when you turn the key to the left (acc), and the post (coil) I attached the white wire too is only hot when the key is turned to the right, as in trying to start the truck. With the key in the center position this post is not hot.
Do not know how the motor kept running???
I idled it down real low and popped the clutch to kill it.
Any suggestions?
Do not know how the motor kept running???
I idled it down real low and popped the clutch to kill it.
Any suggestions?
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Freshman User
Joined: Jan 2005
Posts: 48
Likes: 0
From: Brentwood, TN
And the short I'm referring to is what started this post.
Using a multi-meter it pegs all the way if I put the black contact to the negative post of the battery and the red contact to the disconnected ground cable. Also, just attaching the ground cable to the negative battery post will cause a small spark to occur as it is connected. There shouldn't be anything on this simple wiring setup drawing power when the truck is off, no clocks, etc.
Tracing it down I found the radio was hot when the key was off (clock and channel memory). I re-wired it so the radio does not draw when the key is off.
The only other thing that was causing the apparent short was the two wire connector on top of the alternator. Take it off and there was no short.
Now that I have rewired it, the short exists whether the top wire connector on the alternator is on or off.
Using a multi-meter it pegs all the way if I put the black contact to the negative post of the battery and the red contact to the disconnected ground cable. Also, just attaching the ground cable to the negative battery post will cause a small spark to occur as it is connected. There shouldn't be anything on this simple wiring setup drawing power when the truck is off, no clocks, etc.
Tracing it down I found the radio was hot when the key was off (clock and channel memory). I re-wired it so the radio does not draw when the key is off.
The only other thing that was causing the apparent short was the two wire connector on top of the alternator. Take it off and there was no short.
Now that I have rewired it, the short exists whether the top wire connector on the alternator is on or off.
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Freshman User
Joined: Jan 2005
Posts: 48
Likes: 0
From: Brentwood, TN
The only way the truck would keep running would be if there was power to the ign (coil) post even with the key off.
So, the white wire going to the ing switch post is a hot wire. That's what has to be keeping it running.
So, the white wire going to the ing switch post is a hot wire. That's what has to be keeping it running.
Fleet Owner
Joined: Jul 2004
Posts: 27,290
Likes: 1,055
From: NM
I've seen some diagrams that show a diode in the feed to #1 from the ignition switch; that may be required to prevent run-on. I'll look around, you can too, just do a google search on "GM alternator wiring"
Edit: Yep, here it is:
Terminal #1 on the alternator plug uses about 18 Ga. wire with White insulation, travels through the diode and then to #'1' terminal on the alternator plug.
('Arrowhead' on the diode pointing at the alternator), or else use an idiot light.
Edit: Yep, here it is:
Terminal #1 on the alternator plug uses about 18 Ga. wire with White insulation, travels through the diode and then to #'1' terminal on the alternator plug.
('Arrowhead' on the diode pointing at the alternator), or else use an idiot light.
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Freshman User
Joined: Jan 2005
Posts: 48
Likes: 0
From: Brentwood, TN
My solenoid has 4 posts, battery side, starter side and two smaller posts in the middle. The one on the right hand side is the Ignition Bypass Terminal. It is only hot when the ignition is on and when it's hot it barely lights up my 12 volt tester light. I'm thinking that's why the mechanic ran a wire there last time (of course he ran the red wire there instead of the white one).
So, I'm thinking of hooking the white wire back up to solenoid next to see if that works.
If it doesn't I now understand I'll need to put a 10ohm diode (Radio Shack # 276-1661) in the white wire between the alternator and the ign switch.
Thanks for all of your help!
Now I've just got to find out where that short is coming from!!!
So, I'm thinking of hooking the white wire back up to solenoid next to see if that works.
If it doesn't I now understand I'll need to put a 10ohm diode (Radio Shack # 276-1661) in the white wire between the alternator and the ign switch.
Thanks for all of your help!
Now I've just got to find out where that short is coming from!!!
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Freshman User
Joined: Jan 2005
Posts: 48
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From: Brentwood, TN
A simple question I should have thought to ask up front:
Using my multi-meter with one contact on the outgoing positive connection of the alternator (the one with the red boot isolating it from the case) and the other touching the outer case of the alternator, I have continuity!
Doesn't this prove there is a short in the alternator?
Using my multi-meter with one contact on the outgoing positive connection of the alternator (the one with the red boot isolating it from the case) and the other touching the outer case of the alternator, I have continuity!
Doesn't this prove there is a short in the alternator?
Fleet Owner
Joined: Jul 2004
Posts: 27,290
Likes: 1,055
From: NM
No, it proves the coils are connected on one end to the (+) post and the other to the case. If it will give you peace of mind, take it in and have it tested. You may have fried something having it connected wrong. If there was a dead short in the windings, you'd see it and smell it.
Did you put a light bulb or diode in the wire yet?
Did you put a light bulb or diode in the wire yet?
Elder User
Joined: Feb 2012
Posts: 948
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From: Central Oregon
" I really don't want to replace the alternator for the fun of it.
Any reliable auto parts store will test your alternator for free. That could eliminate the simple problem of a short in the alternator being your cause.
Any reliable auto parts store will test your alternator for free. That could eliminate the simple problem of a short in the alternator being your cause.
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