Charging System Problem

[captfrankie]

My alternator locked up so I replaced it.I've had a problem with the charging system since.When I take a battery cable loose it dies,so I know it's not charging.I took the alternator back to bench test it.It tested good.I have a Black wire which I'm assuming is ground and a green wire.I have a battery/charging system tester.Where do I hook up the Positive and Negative leads of the tester? Should I check the wires to the voltage regulator for continuity next?Then from the regulator to the starter relay?

[digdoug]

What year is your truck?

[712edf]

The big black wire that "bolts" to the alternator is not ground! Its hot wire i believe. The smaller green wire which plugs into back of alternator is the field wire, & I believe its someway connected to the regulator.

Bucky

[captfrankie]

Dumb A$$ me.68 w200 crewcab with slant 6.

[Jeffc]

2 wire system (one green wire, one black), test voltage at back of alt with engine running, should have 13.5+/-, then test at starter relay (large nut on relay were the battery cable hooks), should have close to same voltage, then test at battery- again should have close to the 13.5 volts, if there is a drop of more than .5 volts between the
back of the alt and the battery you have a wire or bulkhead problem (most common)......
as posted above,black wire is the power feed to system and battery.....
green wire comes from regulator to alt to tell alt when to turn on and how much.
Most of the time if the above is a problem with wires--- or bulk head contectors were
the power passes into the cab, pull both sides of the connector clean and retest...

You can also test backward from the battery to alt, key off..... say your battery has 12 volts,
test at the relay, should be close to the same (if not it is a cable problem), test
at the back of the alt (black), should have no more than a .5 volt drop (or 11.5volts).
If you have no power at the alt testing this way, you have a problem in between,
agian bulkhead plugs on the fire wall are a common problem. However, the issue
could also be on the dash with alt gauge since it has to pass the power from one
side of the system to the other >however, alt gauge is not a common problem
and in this case you would not be able to start the truck with the key if it was.
The main thing is to test each area and see were
you have power and were you don't, or were there is a voltage drop....
This test is for the battery to alt only, black wire from the alt changes color to red
after it passes though the firewall.


Next test, unplug green wire from alt, test green wire to see if it has voltage, again key on but engine does not need to be running, if no voltage- it is a regulator issue or power supply to
the regulator (bad wire or blown fuse) or bad ground at regulator. Be sure to clean that
ground wire that runs from the engine to fire wall.

For a system tester, just hook it to both posts on the battery and follow instructions....
The above test need to be done with a mutimeter.....

[captfrankie]

I checked battery , relay , black wire , and green wire.All have very close voltages.I cleaned and sprayed the connections going through the firewall.The needle on the gauge is in the middle and I really can't tell that it moves.I tried using a 12v battery tester when running touching both connections on the gauge,It didn't light up.Is it supposed to?I appreciate the help.

[712edf]

I checked battery , relay , black wire , and green wire.All have very close voltages.I cleaned and sprayed the connections going through the firewall.The needle on the gauge is in the middle and I really can't tell that it moves.I tried using a 12v battery tester when running touching both connections on the gauge,It didn't light up.Is it supposed to?I appreciate the help.

I think your ammeter may be the problem. First both posts on the ammeter are hot. One side is connected to the alternator, the other side comes to the battery. The gauges measures rate & direction of current flow. If the gauge is good, there will be conntinuity through it. If the gauge is bad, but sides will still be hot, but NO current is passing through & all the ignition stuff is on the Battery side of the guage. Unhook battery & she dies.

Your test light didn't come on because both sides of the gauge are HOT (positive).

With everything hooked up normally, turn the key on & the headlights on. The guage should move alot towards the "D" side, if not then the gauge is bad.

Bucky

[captfrankie]

I may put in an aftermarket gauge.Does the black wire from the alternator go to one side of the gauge? Y/N Where then does the wire on the other side of the gauge go to?I'd rather run new wire to the new gauge instead of cutting and splicing old wire.Thanks

[712edf]

One wire on the ammeter is from the Alternator, the other is from the battery. If you hook them up backwards the gauge will read backwards. An ammeter shows direction of current flow (charge vs discharge) & the rate (amperage) of either. Both wires are hot at all times. This is why if you put your foot on the brake (ign key Off) the needle will bump towards the discharge side, due to brake lights drawing current from the battery. Same thing if you turn headlights on.

If you take both wires & put them on the same side of the gauge (either side), this will bypass the ammeter, but the alternator will charge properly if its good. Many owners replace the ammeter with a voltmeter, which measures electric pressure.

Aftermarket gauges (ammeter or voltmeter) will have instructions as to which wire goes to which post.

Bucky

[captfrankie]

The alternator is new and showed over 14 volts when I took it back to have it tested to make sure it was good.I replaced the voltage regulator also.Both the red and black wires at the gauge are hot.I tried an aftermarket gauge.Still dies when Positive cable is removed.What am I missing?Where does the red wire on the back of the gauge go? Can I bypass to figure my problem?

[junior]

How about the voltage regulator getting hurt when the alternator failed and being the problem?

[hobo]

Yep. Wouldn't be surprised if a fusible wire in the regulator went out.

[captfrankie]

I've been fighting the weather but I'm stll trying.I took the old and new voltage regulators in to be tested at the auto parts store.The old probably original showed a little over 14 volts.Well within the range showed in the book.The new one showed a little over 18 volts.Way over.I assume the old is good and the new is bad.
I will put the old one back on.Can I use an aftermarket gauge,new wiring and bypass all the old system? Does the old/original red wire hook up to the starter relay?

[Jeffc]

to by-pass the old system you need to run a new wire from the alt to the starter relay....
Black wire from nut on alt to the nut on the starter relay..... stock wire it 10 gauge and you need to
use at least that size wire, 8 gauge is larger and that is what I would use as a replacement.
A 8 guage wire will allow use of a 100 amp alt if you choose to.

You still need to use the red 10 gauge wire from the starter relay to the alt gauge to supply power
to your dash and fuse box, you can wire a aftermarket voltage guage inplace of the alt
guage using the same wires on the back of your alt guage after you do the wire replacement
by-passing the old charge system wires. I would also add a fuseable link between the relay and
were the wire enters the firewall

[captfrankie]

What amp fuse would you suggest for the fusable link?

[ayatollahgondola]

Interesting,

I'm having precisely the same problem. pull either cable off the battery and the motor dies.