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Alternator not charging battery


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August 17, 2013
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Year, Model & Trim Level
1994 Explorer XLT 4.0L
I've searched and read the other posts about this but am still stumped. My newly replaced alternator is not charging my battery. I'm having to charge my battery every night until I resolve this. Here's a list of things I've done so far:

1994 Explorer XLT, 4.0 litre.

Alternator not charging battery.
Voltage on instrument panel when running is on the "N" with freshly charged battery.
Gets lower on the "N" as I drive.
Not running fan, radio, or any accessories.
Cannot drive it at night for fear of it stranding me again due to lights draining battery.
Replaced alternator 90 amp
Had O'Reilly test battery, where I bought it from in 8/2011, thay said it's good.
Non load battery tests at 12.8 volts
Load tests at 12.1 volts, engine running, no accessories.
12.1 volts engine running, lights on, fan on.
EVM test with negative battery terminal and lug on back of Alt is 12.1 volts, running or not.
There is no fuse between battery and Alt, removed before I bought it.
Fuses on Power Dist box under hood all good. Pulled each one and visually inspected them.
Interestingly, when testing ports that Alt fuse plugs into in Pwr Dist box, it tests at 10.8 V. The terminal next to it that runs the light under the hood shows 12.1 V.
Ohms on negative battery wire is .1, as is positive wire.
Removed negative wire on engine block, cleaned, sanded and replaced.
Fuses underneath dash all good, pulled each one and visually inspected them.

A few years ago, the actuator arm on the steering column wouldn't release the switch, so I re-wired it to start using 2 rocker switches, one for Access., one for Ignition, and a push-button to start it. I've experienced no problems with this at all but am wondering if this could cause a charging system malfunction, but all-of-a-sudden? Also, I read that if the lamp behind the volt meter guage on the instrument panel is bad, the alternator will not "excite" and not charge the system. Mine is dim but not out.

I'm seriously frustrated and perplexed here. Is there anything rlse I need to test? Is there a common issue with this and a common solution? It starts fine when the battery is charged but have had to get a jump on more than one occasion.

Any insight or help is seriously appreciated. Thank you in advance.

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I'd bet the newly replaced alternator is bad.

You should be getting 13.5 - 14.5 volts at the battery terminal with the engine running, anything less and the alternator isn't charging the electrical system. I'd check the wiring that plugs into the alternator for continuity, but other than that I would lay odds that you got a bum reman alternator.

There is a fused link built into the wire going from the alt to starter relay, then to battery .I bet its blown

Alternator tested good. Battery tested good. Pulled the alternator harness off and tested resistance on all wires - 0.0 resistance. Looked for fusible link between the alternator and starter relay and there is none. The O'Reilly guy said it could be possible that the belt isn't spinning the alternator pulley fast enough. The belt looks good - a little weather checking on the rib side and it's tight so I think that's out. The only thing I can possibly deduce at this point is a grounding problem. The vehicle starts fine when there's a full battery charge, but maybe the alternator may not be grounding properly. I really don't know. I just can't figure out why the alternator is not charging the battery properly. Interestingly, when I got a jump the other day, the volt meter on the dash read 14+ volts while the jumper cables were on. It dropped down to about 10 when I pulled them off. Also, the vehicle dies when I pull the negative cable off of the battery. Is this normal? I always thought that it should stay running. Any ideas?

There are 2 fuseable links running parallel from the starter relay to the alternator. at the relay its 2 grey wires that join to connect to the alt in a black wire with orange stripe. the fuelable links look like fat rubbery things about an inch and a half long

There are 2 fuseable links running parallel from the starter relay to the alternator. at the relay its 2 grey wires that join to connect to the alt in a black wire with orange stripe. the fuelable links look like fat rubbery things about an inch and a half long

Yea unless someone has replaced them they should be there.if you don't know what they look like you wouldn't see them

The only thing I see there is a plug. Gray, about an inch and a half long. I pulled it apart and there are 2 male prongs on one side and 2 female receptacles on the other. I don't see any semblance of a fuse inside. There's also one of these on the negative wire.

The 3g alternator is pretty simple... I've done the 3g conversion on a ford with a 2g and will soon be doing it on another..

Here is a short description of where the wires go..

The output connector (B+)which basically just gets to the battery.

The A wire which basically just needs to end up at the B+

The I connector ends up with switched power (hot when in run)

The s connector jumps over the the single connector on the alternator.

So, what you need to check is that your have 12v on the I connector on the the alternator when the key is in the on position. This is where you normally have the issue..

The I connector gets it's power from the ignition switch (under the dash) and it goes through the cluster. That means if your charge light is dead or missing or some other wire is broken there you won't get power to the I terminal. The 15 amp fuse in the fuse box (under the hood) is in this circuit so if its blown you won't charge either.

You also should have 12v at the A connector AND at the big connector (b+) on the back of the alternator.. Thats an easy check and I don't think I've seen that cause the issue other than the time the fuse wasn't in when we did the conversion.

Now, for the fusable link. Its just a wider part of the wire. Most time it just looks like someone put lots of electrical tape on a 1" section of the wire OR if its not covered it will look like someone put something around the wire that is about 1" long.

Here is a diagram of how the 3g alternator wiring goes (including info about the charge light and I terminal).

Also, just in case your alternator isn't labled as to which plug is what (I,S,A etc) here is a pic of what is what.


GOT IT! I tested the I receptacle on the 3 pronged plug with the ignition on and there was no power. I mentioned before in my post that I had bypassed the key switch to a push-button start system. In looking under the dash for any shorts or disconnects, I thought about the original reason I had modified the ignition system to begin with - the actuator arm on the steering column would not disengage and the car wouldn't turn off. I remember accidentally turning the key all the way a few weeks ago when syarting the motor. Apparently, the acuator arm did not disengage and the starter switch was on the whole time, though the system was not energized. Using a needle-nosed plier, I pulled the arm backward to the "Off" position and the tested the I wire on the Alt. plug. Sure enough, I had 12+ volts with the modified switch on. It started right up and I now have 14.6 volts at the battery/alternator with the engine running. Problem solved. Though I may have not needed a new alternator, the volt meter now reads higher than it's ever been, so I'm telling myself that if I didn't replace it, it would have needed to be eventually. That's my story and I'm sticking to it.

Thank you all for the help and input. These posts and your knowledge have been invaluable in helping me solve this "needle-in-a-haystack" problem.