Engine/Transmission (1994 - 1998) Alternator and gen light is on

[Neibe]

Today my Gen light came on and the alt gauge shows only 12v instead of the usual 14v. Went to auto zone and they said the alt is only putting out 89 amps should be 136 amps. Could it be something other than the alternator?

 

[K5IP]

Even if your alternator is only providing 89A, that is not your problem. It only takes a few amps to raise tha battery voltage from 12Vdc (no charge condition) to 13. 5Vdc (a light charge rate). Obtaining your previous 14Vdc level may require a bit more of a charge, especially if the battery has been discharging for a while, but if your charging system is working at the 89A level instead of the 136A, you would probably not be aware of it.

You are right, it probably is something other than the alternator. Does your tach work? The charging system needs an innput from the engine speed sensor to work.

There is also an auto shutdown relay involved in this which can also be a problem.

There is also the possibility of an open fuse in the output of the alternator (big fuse)

If you have shorted the alternator output terminal (big sparks) look there.

If you need step-by step help, PM me and we can work through it.

Rog

 

[San Felipe Bob]

Check the brushes on the alternator!

I had 2 auto zones tell me my alternator was just fine. Don't trust them. :-{}

I checked the brushes and they were history... :{

Wow the trans works so much better with a new alternator. Oo. From Auto zone too lol.

yeah I was amazed!



SFB

 

[JGK]

Take it to an alternator repair shop and have them test it. They can do it on the truck while you wait.



If it needs fixing they can be rebuilt. Had to do mine yesterday. I did the R & R, they rebuilt it. $95 total.



If you do this and you choose to R & R the alternator yourself, make sure you disconnect both grounds from the batteries first before disconnecting any wires on the alternator. This is mandatory. Failure to do so can result in frying a lot of your electronics (PCM). With that in mind, its a real easy job.



-Jay

 

[JFaughn]

It sounds like 2 problums , the low amps may be the brushes , but the 12 volts is something to do with the field , one end goes to the battery via fuses ect , the other goes to reg. , depending on specific yr mod , do not have wiring diagram at hand , but on mine , 94 , the voltage reg. is in the computor , but with yours it is also dependent on other sensors confirming that it should ground , to a varying degree , so whats happening is the one side of the field is always got connection to the battery + , and like every other device that the computor controls , it does it via grounds , thats why its very important for it to have very good grnds. , if not then the computor will find its own way to ground , and thats what kills computors .

 

[Neibe]

Well this morning my alt gauge went right down 8v the lowest setting on it. My lights got dim turn signals wouldn't work but the tach still worked and all of my gauges still worked. So I'm going to replace the alt only to find out autozone gave me the wrong one. The connectors on the back are different. Mine are bolted on the new one looks like it has a clip on connector.