How to I test the rest of my charging system circuit?

Tiny
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  • MEMBER
  • 1999 CHEVROLET CAVALIER
  • 2.2L
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 136,500 MILES
My vehicle stopped charging. I replaced with 4 different alternators and they were 3 used and one rebuilt that all passed an alternator test at my local parts store off of the car. Even though I was putting crap alternators on due to temporary financial limitations, I'm finding it hard to believe that they were all bad, even a rebuilt one. I have a multimeter and understand the fundamentals of electricity but don't have any flow charts, am not familiar with the other system components or their specifications and want to know how I can verify the rest of the charging system circuit for any other possible problems? Can I verify just the alternator function itself on the car even though they all passed off of the car? The rectangle connector has 4.85 volts and good ground to it. The big cable terminal on the alternator is also reading about 5 volts with the engine running. It read 10 volts with one of the alternators. My battery is fully charged and passes a load test and is a day old. Where do I go from here to not just be guess replacing parts but know for sure?
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Saturday, October 10th, 2015 AT 10:51 PM

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Tiny
CARADIODOC
  • EXPERT
Hold on a minute. There's no ground wire in the small connector. There should be a brown wire that goes to the dash light. That's the turn-on circuit for the internal voltage regulator. You should find around two volts on that wire and the dash light should be on with the ignition switch on and the engine not running. That will go up to near 14 volts to turn the dash light off once the system starts charging.

You must always have full battery voltage, 12.6 volts, on the large bolted-on output wire on the back of the generator. If that is different than battery voltage, there's an open fuse link wire or blown fuse. That circuit goes right back to the battery positive cable, but on GMs that is usually tied to the starter solenoid for convenience.

To tell if the charging system is working, measure the battery voltage with the engine running. It must be between 13.75 and 14.75 volts.

Starting with the '87 model year, GM went from the second best generator to by far the worst design in the world. Due to that design, they develop huge voltage spikes that can damage the internal diodes and voltage regulator, and interfere with computer sensor signals. The battery is responsible for damping and absorbing those spikes, but as they age and the lead flakes off the plates, they lose their ability to do that. To reduce the number of repeat failures, replace the battery, as you did already, unless it is less than about two years old.
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Saturday, October 10th, 2015 AT 11:21 PM
Tiny
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Catadiodoc,
Thank you so very much for responding with such awesome and excellent knowledge. I'm guessing that since the big cable terminal on the back of the alternator is not reading battery voltage with key on or while running that I have a blown fuse able link from what you've explained. I never was able to find a fuse for that circuit. Where is that fuse able link? Do I need to tear into the harness to locate it or do they make it more accessable? Is it hard to locate? Can I bypass it and install another fuse able link if I can't find it? Does it run between the starter and alternator and then to the battery or how does it run? I can go buy a cable with an alligator clip on each end. To bypass the fuse able link and test, should I hook one end to alternator terminal and the other to the positive battery post or where to see if the system will then begin charging? Do you agree that we have lost continuity in this part of the circuit and that it's probably that fused wire? Is there a relay in the circuit that could be failing or probably just the fuse able link? By the way the charging voltage was non existent with the engine running. It was just 12.6 battery voltage on the battery posts. I changed the battery already with this last alternator that I put in yesterday and only started it for 90 seconds. I even took it to Auto Zone, recharged and retested it. I know the battery is good. What do you recommend?
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Sunday, October 11th, 2015 AT 1:13 AM
Tiny
CARADIODOC
  • EXPERT
A fuse link wire is a regular wire but of one gauge smaller than the wires it protects, so it's the weak link in the chain. The insulation is designed to not burn or melt. The advantages are they aren't susceptible to loose or corroded terminals like regular fuses are, and they will withstand a temporary overload from a motor that's starting up without nuisance blowing. The disadvantages are they're relatively difficult to replace and they're often in places that are hard to get to. They're often buried because they typically never need to be replaced for the life of the vehicle.

Chrysler commonly put theirs all together in a bundle that runs around the left strut tower. Other manufacturers usually place individual fuse links in the wire they protect, so they can be found anywhere on the vehicle. GM liked to connect them to the large terminal on the starter solenoid. That was done for convenience since that was connected right to the battery positive post. The disadvantage to this is they sometimes get forgotten when replacing the starter.

The ways to identify a fuse link are by their dull color compared to regular wires which are shiny, and by the splice. The typical fuse link wire is four to eight inches long, and at the end is a terminal, heat-shrink tubing, or a plastic block. When you buy a replacement, you get about 12" of wire. That can be cut to make two or three repairs. The length when installed is not important. Just as with regular fuses, fuse links are color-coded to denote their current rating. The common colors are orange, gray, white, black, and green.

You can repair a fuse link by splicing the burned ends and sealing the splice with heat-shrink tubing, but at least a part of the finished repair has to keep a single wire intact. If the wire is doubled up for its entire length, that will have double the intended current rating and won't protect the wiring. The recommended repair involves cutting off all splices, then soldering the new fuse link wire to the ends of the regular wires. Always solder the splices and seal them with heat-shrink tubing. Never use electrical tape as that will unravel into a gooey mess on a hot day.

When you look at your starter solenoid, you'll see the battery cable bolted to the larger terminal, and there will be at least one much smaller wire bolted to that same terminal. That is often the fuse link wire starting right there. To test it, tug on it as I mentioned before. If it's burned open, the insulation will stretch very easily.

You can use a clip lead as a temporary jumper to verify everything else is working. The generator will never produce its maximum current except when the system is being load-tested, so the jumper doesn't have to handle much more than 40 - 50 amps if the battery is run down and is recharging. With the fuse link burned open, if the charging system is otherwise working, you'll find abnormally high voltage on the generator's output terminal unless the voltage regulator has things well under control. Fifteen to 18 volts is often found at that terminal while battery voltage stays at 12.6 volts or less.
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Sunday, October 11th, 2015 AT 9:08 PM
Tiny
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I just wanted to say thanks for helping to get me back on the road when I really needed it. Your info was perfect and really pointed me in the right direction. The best hints were anything other than battery voltage on the back of my generator would indicate an amount of resistance that points to a fusible link and also that GM mounts them on the solenoid. I simply probed for the one with the same funny voltage and changed that one. That gave me battery voltage to the generator which activated it to over 14 volts but it didn't make its way back to the battery until I changed the second one next to it. I think that one of those wires was worn due to heat from the starter and resting on the starter which might of shorted to ground and blew both of the fuses unless one of those various used alternators had a serious problem. I think it was the wire. At any rate, everything is working great now and I can't thank you enough. I'll send you a small donation as soon as I get caught up on things for your services which I think are valuable and helped me a lot.

God Bless
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Thursday, October 15th, 2015 AT 7:40 PM
Tiny
CARADIODOC
  • EXPERT
Dandy. Happy to hear it's solved.
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Saturday, October 17th, 2015 AT 7:51 PM

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