1988 Suburban, battery won't charge

[unixfmike]

777stickman, I do have voltage gauge built in to the dash. That voltage reading is normally just under 13 volts (center of gauge), which is faily close to the 14.44 - 14.5 volt reading from my multimeter on a freshly charged battery. I took the gauge panel apart today and tested all bulbs, no faulty bulbs. I have traced the red wire from the positive battery post to the alternator. The wire is a straight shot with no other connections in it.

aztecf/jeff, I have not yet tried jumper cables from the alternator case to the negative post (if I understood you correctly), please correct me if I am wrong in my understanding. If this is the cause of my problem I'm going to really feel like an idiot for wasting everyones time.

I have posted a picture at http://unixf.com/pics/88_chev_sub_alt_plg.jpg
that way you can see my tests and other questions. Thank you for all the help so far, I greatly appreciate everyones help.

--mikew
fort sill, ok

[unixfmike]

I changed the fuse, no change. I can't seem to find any jumper cables (that's always my luck too) at the moment to test for a good ground . Look's like I'll trading batteries again for a few more days.

--mikew
fort sill, ok

[spyder2000]

I hope I didn't miss it in the thread, but I see a lot of discussion regarding battery and alternator voltages. My question is have you or autozone tested this alternator for amperage output? (Don't try this with a common multimeter as most of them only read up to 10A or so.) You should also check to see how much AC voltage is being delivered. Low amperage and AC voltages are signs of defective diode bridges.

AC voltages will not charge your battery and low amperage output can't supply enough current to drive the fan in your ventilation system for long. The battery will power these for a while before it dies.

[unixfmike]

I have taken the alternator back to Autozone (4 days ago) and it did pass all tests on their diagnostic machine. The sales clerk who helped me did not do a seperate amperes test.

--mikew
fort sill, ok

[jdl]

Everybody has some good ideas.

I was looking at a trade publication, yesterday. It had an alternator section. It said from 86 to the mid 2000s, that the majority of GM alternators used the same pin configuration in the connector. The connector may be rectangular or oval, but the pin layout should be the same, not all, but the majority. The terminals should be labeled P-L-I-S or P-L-F-I, may be hard to see. On these type alternators, it should work fine with only the L-terminal going to the connector. On these type alternators the L, excite, terminal is always next to the P terminals.

If the only problem is excite voltage, you can run a new wire to the L terminal, come off ignition voltage, use a resistor in the circuit, trying to use straight battery voltage without a resistor/ load on the circuit isn't a good idea, I believe several different sizes of resistor will work, 500 ohm, is one.
The connection to the L-terminal has to be GOOD or it won't work. The best way, is to use the proper connector and plug straight into the L-terminal. In the past, on different GM models, where I knew there wasn't any excite voltage to alternator, I have tried backprobing the L-terminal at the connector, with a wire and resistor coming off battery voltage, just for a test, it still wouldn't work, I don't think I had a good enough connection.

I have an 88 chevy work car in the drive, no charge lite, but a volt-meter on the dash. Some of the info I posted here came from this months issue of motor magazine, they have a web site, motor.com, I haven't checked to see if this months issue is posted, yet. It is interesting.

I'm sure all you folks know more about vehicles than I, but,To use any information from any web-site like this, you need to know what your doing. I enjoy this web-site, informative and the people are knowledgeable.

[unixfmike]

The alternator is clearly marked "S L F P", which is kind of mind bogling because it does not match any of the wiring diagrams I have for that year and model of truck/alternator. The alternator does have a warranty on it, so I might just go check my electronics parts bin for a 500ohm resister and some wire. If all I need to do is hit the "L" with a hot wire -500ohms that might make my day, or make me all tingly! I'll give that a shock tomorrow when I have some daylight. Thank you for that suggestion.

--mikew
fort sill, ok

[jdl]

For testing purposes, you can wire the L terminal hot, using a resistor in the circuit, but don't leave it that way. If you have to wire a new circuit, come off ignition voltage, that way the circuit is only hot, with the key in the on/run position. When the key is off the circuit is dead.

I don't have a wiring diagram for the excite circuit. The order you listed the letters, is not what my info shows. It may not make a difference. On GM alternators, I've never seen it where the L terminal was anything but the excite terminal. You have to make sure the problem is the excite voltage and not something else. My info has to be general in nature, because I can't see your alternator from here.

Did you get a chance to look at the article on the motor site?

[unixfmike]

I finally threw in the towel and decided to use a workaround. Since the "F" wire comes off the iginition and is fused for the volt gauge, I decided to connect that wire to the "L" wire with a light bulb in the circuit for some resistance. The bulb only comes on momentarily between having the key in the on position and having started the engine. Once the engine runs for 2 or 3 seconds the light shuts off and the alternator starts charging. I checked this morning and the battery was at 12.03 volts. With the engine on the battery voltage was consistently at 14.3-14.41 volts. Once I shut the engine off the voltage at the battery was at 12.92 volts. After a day of driving the battery is still holding a charge higher than what I started the day at. This is just a temporary fix so I don't get stranded at the road side. For now it works. Thank you everyone who came up with the suggestions and for all the help. Walking home with a car battery to charge is frustrating.

http://unixf.com/pics/CSSeries_excite_workaround.jpg


--mikew
fort sill, ok

[Borguy]

Now that your alternator is back in bussiness, here is another thing :
Do you have a thick wire going from the + at the battery to a junction(box) somewhere (fuse/relaybox, fireboard, ...)?
If so, you can lead a wire from the "S" (Sensor) on the alt. to this junction.
It will help the regulator maintaining a steadier 14.4V.
When there is a surge of power by several users (fans, lights, ...), the voltage drop will be higher at that junction point than at the alternator and/or battery.
With the Sensor at that point, the regulator will react more accurate.

[Austininne]

I have a 1988 chevy blazer 2.8l with the exact same problem. Replaced alternator, battery, and battery cables. Need to know where to go next! Does anybody have a wiring diagram for this? Please help.

[MT-2500]

Originally Posted by Austininne

I have a 1988 chevy blazer 2.8l with the exact same problem. Replaced alternator, battery, and battery cables. Need to know where to go next! Does anybody have a wiring diagram for this? Please help.

This post is old and started by someone else.
To save on highjacking expense and to get help with your problem hit the New Thread button and start new post and give all info.