My 99 Ranger charges intermittently. Sometimes it is just fine, sometimes the voltmeter drops and the light comes on. Might go a mile, might go all day without an issue. Alternator was replaced 2 weeks ago. Any ideas where to look? I haven't ruled out the possibility of a bad "new" alternator, but I haven't been able to get it to act up when I actually have time to start diagnosing it. Is there a relay somewhere that could be causing this? TIA

 

Seeing as how the alternator & battery connections have recently been messed with, double check to make sure they are all clean bright & tight on both ends. At warm idle, you might try a wiggle & thump test on the wires & connections to see if you can induce the problem.

This would also include the under hood power distribution box located 30 amp alternator field fuse, its connections & the wire from the alternator to the field fuse. If the field fuse, wire, or its connections on either end are corrupt, it could interrupt the alternator field from exciting & cause intermittent output.

If all that checks out ok, look at the serp belt, tensioner & pulleys, for fluid contamination, condition of the serp belt & the tensioner molded in tension range marks, to make sure belt tension is within range.

If all that checks out, hook up your ELM scan tool the next time you drive it, so it can capture a snapshot of what's happening when it acts out & post up All trouble code Number clues it finds, as they can help focus your trouble shoot.

A bunch of thoughts for consideration, let us know what you find.

 

+1 to pawpaws xlnt post. Theres also mini fuse 15 7.5 amp in the fuse junction panel. It's wired to the idiot light and to the voltage regulator circuit in the alternator. Make sure it's not loose in it's holder.

 

If you have a separate regulator, it can cause the intermittent problem described. I guess a built-in regulator could also.
I would check by connecting a voltmeter across the battery + & - terminals, and starting the engine, then add and remove loads such as blower motor and headlights. A good system will respond to the change, and adjust output to counter the added load or at least come close. Charging voltage should be in the mid-14v range, and will dip as load as added, but should recover within a second or so.
The intermittent regulator problem will show as the at-rest battery voltage will not increase immediately after the engine is started, but will instead vary as the alternator is regulated into action or left at rest.
tom

 

I jiggled and wiggled, removed and reinstalled the 30 and 15 amp fuses mentioned above and it seems that it may have cured the problem. Hopefully something was just loose. Hasn't acted up the last few times we have driven it. I knew there were fuses in that circuit but wasn't sure which ones they were. We shall see.......

 

Ok, good feedback on your wiggle test.
A few members have reported finding corrosion on their under hood power distribution box fuse & power relay connections, so you might have a close look at the under hood alternator 30 amp field fuse contacts & if any corrosion is noticed, tidy it up with a good plastic safe electrical contact cleaner spray. I'd disconnect the battery B- cable while spraying around the power distribution box electrical contacts.

 

I saw no corrosion on any of the connections.......I think one of the fuses was just not pushed in tight. But we shall see.......

 

2000 Ranger 4x2 (2.5l) charging issue All appreciate your posts to the alternator problem - On way in to work this morning I had the same problem as 78 PEB except as I got closer the problem tended to become a hard failure verses an intermittent problem. Unfortunately I do not have a meter with me to check the voltage across battery while adding removing loads. Anyways I had this same problem approximately a year ago and had my alternator replaced and had some of the same problems 78 PEB had in the beginning but then the battery light went out and no problems until now. 78 PEB why did you replace the alternator a couple weeks back? If I make it home tonight I will check all of the items pawpaw mentioned and all of the other items mentioned in the other posts and report back. Last year when I had the alternator replaced I had always thought something was not quite right and I hoping to find something like a corrupt connection.

 

My alternator was definitely fried when I replaced it. I was driving to work and the voltmeter dropped and the light came on. I pulled the alternator off and it had gotten hot enough that it had melted the varnish off of the windings and had hardened residue dripping out of the alternator case, I'm hoping it didn't melt any wires or anything else. Since I wiggled the fuses and inspected their connections, I haven't had any more problems.

 

Like I said the alternator was replaced 1 year ago so I can't see the alternator going bad but a corrupt connection would explain a lot also the problem is same as last year maybe the corrupt connection and temperature. I will post the status later today after I hopefully make it home.

 

I made it home with the charging light coming on and off. I arrived in driveway and left the Ranger running and grabbed my meter and checked voltage across the terminals (battery light on) read 15.10 and wiggled wires to alternator nothing concrete as far as a smoking gun. Light went out and vdc was 13.95 then turned on AC and light came on vdc reading was then 12.13. Then wiggled wires to the alternator and light went out but dont know when. From that point on the vdc was 13.9 and did not see the light come back. I will chance it again tomorrow morning and gather more data. Question - does the alternator have a replaceable voltage regulator? Can I go out and buy one and only replace the voltage regulator? I turned off the Ranger and pulled the Alt fuse under the hood and replaced also pulled the fuse inside Ranger and replaced and started again and no light. Hopefully all of the above is understandable.

 

Yes, the kits that the alternator rebuild sites sell include them as part of the package. If you can dig up a part # the auto parts jobbers probably have them too.

 

Using your smart battery charger, put the battery on a slow/ rate of charge, say 4-6 amps over night, to Slowly bring it back up to a full state of charge, so the alternator & battery don't have to fight each other tomorrow.

Look for a loose, or corroded connection at the place you wiggled the wires. Make sure the alternator & battery cable connections are clean, bright & tight.
We only have 12 volts or so to work with, so it doesn't take much resistance in the circuit to cause mischief.

 

Was the replacement alternator a new, reman, or rebuilt & did it come with a warranty?

 

PawPaw I don't have a battery charger and the alternator was a new alternator. I drove into work this morning and no dummy lights came on, I had lights, wipers and the air and nothing. Obviously I will be keeping an eye out for anything. This weekend I will take a closer look at all the connections.