Dumb battery mistake
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Fleet Mechanic
Joined: Sep 2012
Posts: 1,608
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Dumb battery mistake
My daughter and I changed over her entire front end. Rad support, fenders, inner fender wells etc. All was fine until I asked her to reconnect the battery. The previous owner had put a black lead on the positive line from the solenoid. I rushed over to see and hear a fuseable link burn. She had installed the leads backwards. I have a parts truck so I took this part of the wiring harness out of it and did an exchange and still the truck will not start. Any thoughts?
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Fleet Mechanic
Joined: Sep 2012
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OK. So I spent some time thinking about all I did. I also replaced the rag Joint. It seems that when I pulled up the steering wheel, I misaligned the NSS. So the NO START is repaired. But I do not have a horn. I did run a jumper wire over the rag joint to each side, but no power at the horn wire. Can you help on this?
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
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Fleet Mechanic
Joined: Sep 2012
Posts: 1,608
Likes: 53
fmc400,
I am glad you are helping with the electrical. I am seeing you have many posts in which you have helped out with this problem. I have a larger problem, the truck does not seem to be charging. I am not sure what other damage was done when she crossed the leads. So I am now going to read up on some previous posts to see if I can start to narrow this problem down.
I am glad you are helping with the electrical. I am seeing you have many posts in which you have helped out with this problem. I have a larger problem, the truck does not seem to be charging. I am not sure what other damage was done when she crossed the leads. So I am now going to read up on some previous posts to see if I can start to narrow this problem down.
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Fleet Mechanic
Joined: Sep 2012
Posts: 1,608
Likes: 53
fmc 400,
I just found this in a thread: From you,
When the battery is connected backwards, all six diodes in the rectifier bridge are forward biased, and act essentially as a short. In the absence of any current limiting, these diodes will blow. However, the output of the alternator is protected by a fusible link (separate than what appears at the starter solenoid).
This fusible link is installed specifically to protect the alternator if the output is shorted externally. It's desirable for the fusible link to blow before the diodes if the battery polarity is reversed. However, this does not always happen in practice; as such it's common to face a puff of smoke followed by a no-charge situation following polarity reversal. It's not guaranteed protection by any means and it really falls upon the owner to simply not do this, as you describe.
So I believe I need to test the alternator first, I believe.
I just found this in a thread: From you,
When the battery is connected backwards, all six diodes in the rectifier bridge are forward biased, and act essentially as a short. In the absence of any current limiting, these diodes will blow. However, the output of the alternator is protected by a fusible link (separate than what appears at the starter solenoid).
This fusible link is installed specifically to protect the alternator if the output is shorted externally. It's desirable for the fusible link to blow before the diodes if the battery polarity is reversed. However, this does not always happen in practice; as such it's common to face a puff of smoke followed by a no-charge situation following polarity reversal. It's not guaranteed protection by any means and it really falls upon the owner to simply not do this, as you describe.
So I believe I need to test the alternator first, I believe.
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Fleet Mechanic
Joined: Sep 2012
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I spent some time cleaning up ground and wires. I check the voltage across the battery and have 12.56 after I started I have 13.56 I believe these numbers are correct. I am NOT at my jeans right now. So I can leave the truck is now charging. Am I correct? I went to test the horn is still does not work. I put a test light cable grounded to the battery and touch my first wire on the horn relay and the sounded. what would be my next move to determine why the horn does not work?
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
The old post of mine that you pulled up is correct; often times, when the battery is connected backwards, the alternator can take on damage. However, the numbers you measured indicate the alternator is charging, so you most likely lucked out.
When you hooked up the test light, you probably hit the wire from the steering wheel that grounds out and triggers the relay (a test light can be low enough resistance to make the relay work). This would seem to indicate that your jumper across the rag joint isn't working. Take the horn pad off and expose the steering wheel nut. See if there is continuity between the nut and solid, unpainted metal under the dash.
When you hooked up the test light, you probably hit the wire from the steering wheel that grounds out and triggers the relay (a test light can be low enough resistance to make the relay work). This would seem to indicate that your jumper across the rag joint isn't working. Take the horn pad off and expose the steering wheel nut. See if there is continuity between the nut and solid, unpainted metal under the dash.
Moderator & parts slinger
Joined: Feb 2007
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From: S/W Missouri, Polk county
Since you are in great hands with fmc400, I'll only throw out a cheap preventive measure. Change the leads to be the correct color or wrap black elec tape around the red one.
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