I recently replaced the alternator on my truck and although I connected the wires on the alternator as they were on the old one, my battery isn't charging. I checked the wiring and I noticed that one wire is disconnected somewhere. all the wires are still connected to the alternator, but one ends with a plug that isn't plugged into anything. Any ideas?

 

What year truck?
There's 3 different systems on these trucks

 

sorry, forgot to put that bit in. 85 F250 w/ 460 4 spd

 

Do you have the alternator with the large stud on the back that is labelled battery and you hook the wire on with a nut? Or do you have the model that all the wires just plug in, and has no regulator on the pass side fender?

 

two studs that the connections just push onto and one more that the eye connection is nutted onto

 

On that nutted connection, see if you have power there with the truck completely off.

Here's how the wires go.

 

Tug on the black/red wire at the solenoid, and make sure the fusible link hasn't blown. If it don't move, it's ok, if it moves, like Dave said, your link is blown, and you will have no power at the stud on the alternator.

Another problem with that style alternator, the connections at the alternator had a habit of getting hot, and melting. They sell a patch kit upgrade at Napa to fix that if that is your problem

 

That one sounds like you have an external voltage regulator. I t should be a blue or maybe silver box with a 4 pin plug. You may only have 3 wires going to it. It may be bad.

Like Dave said, see if you have battery voltage at the large stud with the engine off (be careful not to short it to the block). At least you don't have the dreaded 2G unit with the self igniting plug.

 

Checked the wires, pretty sure the one that is unplugged is the choke wire. Replaced the voltage regulator and I'll have to check the battery charge when I get home from work but I'm pretty sure its still not charging. And now turning on the headlights will make the truck quit, though not everytime. And sometimes when turning them on makes the truck quit, turning them on prior to starting the truck will work. to summarize, I have the following electrical issues:

1) No power to the ignition switch, truck has to be started by turning the key while using a push button to jump from the battery to the front of the starter solenoid.
2) Alternator may or may not be charging the battery (will have to retest with the new voltage regulator)
3) Turning on the headlights will occasionally make the truck quit.

All in all, the electrical system in my truck is FUBAR, or at least it is beyond my capabilities and time to repair.

 

Your ignition switch may be back feeding through your alternator. Not the key, but the actual switch on top of the column. You also need to check the other fusible link on the solenoid.

 

The ignition switch on top of the column was replaced by a garage while I had it in for smog repairs. A few weeks later I replaced it again, thinking it may have been a bad part out of the box and since its a $10 part, I figured it couldn't hurt to check.

 

There is a green/ red tracer wire from the ign to the voltage regulator. If that is not Hot with the key on, you will not charge.

The fusible link from the solinoid should turn into a yellow wire to go to the Ign switch. that stays hot all the time.

Dave, or Chris should be along and give you a wiring schematic , I have no way to do it.

 

Oscar - get yourself a volt/ohm meter if you don't have one, it's virtually impossible to diagnose electrical problems like this without one....

 

have you checked the voltage regulator/If the voltage regulator is bad you will not be charging the battery .On a external voltage regulator you can check to see if alternator is charging by full fielding the allternator .To do this unplugg the voltage regulator run a jumper wire from a to f .alternator to field The harness is marked .you can get a jumper block at ant parts store.when the alternator is full fielded at a idle you should have the amp output of alternator lets say 50 amps when engine is reved up to 2000 to 2500 rpm this amperage should double.you put the amp gauge on the battery wire going to alternator.Usually if fuse link wire is blown or melted to solenoid the engine will not crank.If amp out put is low or none when full fielding alternator than your voltage regulator is bad /Also note on a charging system you must check all componants battery voltage regulator and alternatorIf your battery is bad your charging system won;t work so check battery first charge up and draw test it

 

Have you checked this yet?

Also check the voltage at the battery with the truck off, and with the truck running. No voltmeter? You are dead in the water till you get one.