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I have a 1986 ford Ranger. I can charge it and it will run as long as the Cables are attached to the car jumping but if I remove them the truck will die after about 5 minutes. It sounds like a alternator to me but I'm no mechanic

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  • make sure all the related fuses are ok. if there isn't voltage on the field wire the alternator won't charge.
    – Ben
    Sep 12, 2016 at 20:06
  • Test the voltage of the battery with the vehicle off and with the engine running. should be > 13.5 volts running if the alternator is working.
    – cory
    Sep 12, 2016 at 20:21
  • Wondering if it might be a bad battery as well as a bad alternator. Most cars should run for quite a while on battery alone - if it's fully charged. If it quits after only 5 minutes, there's not much juice in the battery. Mind you, if the battery was discharged, and it only had a few minutes of boost, there won't be much of anything in it to keep the engine running, no matter its fitness.
    – Anthony X
    Sep 12, 2016 at 23:22
  • @AnthonyX it wouldn't surprise me if a dead alternator meant the battery had been drained too much too many times - your "as well" is spot on.
    – Chris H
    Sep 13, 2016 at 7:47

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It does sound like an alternator. If your battery is dying once you remove the "charge" from it, JumpPack or jumper cables, then yes it is most likely the alternator. If your instrument cluster lights are ALL coming on, that is another side effect of a dying/dead alternator.

My advice would be to go to AutoZone or Advanced Auto and have them test your alternator for you. They will test it for free. You can most likely pick up a new one there - you can even trade your old alternator in as a discount off of the price of a new one!

Good luck!

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  • Less of a 'discount' more of a 'you have to and you also pay the core charge upfront'. Less nice put that way.
    – Insane
    Sep 12, 2016 at 22:52
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First of all, I'll warn everyone else just as I did in this answer, please do not remove the battery connections while the engine is running. If your alternator wasn't bad before, this is a good way to make it bad. This is a very old school method of checking a generator while the engine is running, but can fry things on your alternator. Very bad idea.

The best way to check to see if the alternator is charging while it's on the vehicle is, while the vehicle is running, place a multimeter on the negative/positive connections of the battery and see what it's doing. If the alternator is working, you should see a steady reading of ~13.1-14.0vdc (could be a little less or a little more ... what you are looking for is a steady charge). If you see something like 12.0vdc and then it's steadily declining by small increments, this is a sign you should take it in to Autozone or the like and have them test it. If the voltage is declining at a steady rate, it's probably bad.

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I'm no mechanic either, but if this is consistent - then Yes it does appear the alternator is not working at all. Tap it gently with a hammer as the brushes may be stuck, but don't hit it hard enough to cause damage. Check all the connections for corrosion too, even at the coil.

If you have a volt meter you can measure the output from the Alternator - which should be quite huge if it is working and you rev up a little.

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A 1986 Ford Ranger should have a external regulator and use a fusible link in the line running from the alternator to the starter relay.
The link is for charging of the battery only and does not provide for the primary fuse block circuits. If your dash panel "idiot" light is not flashing (provided the bulb is good), a look at the wiring (starter to alternator) and fusible link would be a good place to start.

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