alternator problem 1996 blazer

Hello
I`ve just bought a 1996 blazer 4,3 LT. On My way home suddently the speedometer and the buttons for the 4wd contra 2wd stopped working. I also lost the power from the alternator. After about 30 km. I ran out of battery and the car stopped. Lucky I just made it home.The gauge fuse where also broken. I contacted a repair store and they told me to replace the alternator, so I did. The old one was according to them broken. After replacing the alternator the same fuse broke again. When I replaced the fuse with a higher ampere ( 20A to 25A ) it worked, but I can hear that the alternator is working hard and it is getting varm. The Voltmeter shows only about 10V. To me it seems like this fuse controls the headlights, the charging the 4wd buttons the gauges and the dashboard light. Can this be right? Now I don`t know what to do. I belive that I brake the alternator again if I run it like this, anyway it dosent give me enough Volts.
I live in the north of Norway so the workshops here are not familiar with american cars, so please help anyone if you can.http://www.automotiveforums.com/vbulletin/images/icons/icon7.gif

Best regards
John Martin

10V says the alternator is not charging, voltage should be approximately 14 volts with the engine running. Fully charge the battery before starting the engine, then test the voltage. Is the red battery icon on the dash illuminated? The 10gauge wire on the rear of the alternator must read battery voltage at all times. The brown wire should read battery voltage when the ignition is in the RUN position.

Thank you for your replyhttp://www.automotiveforums.com/vbulletin/images/icons/icon7.gif
The Voltmeter shows 10 V wether the engine is running or not. It didn`t react when I connected a 12V jumpstart either. The red battery icon on the dashboard goes out when the engine starts and the alternator gets real hot after a few minutes. The troubleshooting is differcult when the same fuse that shows the voltmeter makes the alternator overheat. Before I start the engine the message: "check gages" comes up on the dashboard but I don`t know what it meens. It goes out when the engine starts.

The check gages light before starting is normal. It monitors all of the gages and when one or more are out of spec, it turns the light on.

With the engine off: Check for battery voltage with a voltmeter, (not the one on the dash) at the red wire on the rear of the alternator. It must indicate battery voltage is present. The red wire comes from a fusible link that may connect at the starter or at the underhood fuse panel.

With the key in the RUN position, (engine off) check voltage at the brown wire on the alternator. It must indicate that battery voltage is present.
The fuse for the brown wire is fuse #4, a 10 amp fuse. Do not use a larger fuse. Post back your results.

Thank you for helping me out.
I will do as you recommend, and I will reply the results.
Now its past midnight here so I have to do it tomorrow
good night.
Best regards
John M

Hello again
I have charged the battery and it gives approximately 12,5 V. The red wire on the back of the alternator gives the same. When I started the engine without the fuse (that blows) the Voltage messured on the battery went down a little. it encreased a little ( Don`t know exact because of a poor measure instrument) when I replaced the fuse. When I rushed the engine it encreased even more. I have to replace the 20A fuse with a 25A so it wont blow. It`s no doubt that the altrnator is working very hard when the fuse is connected it is alsow getting varm. This I belive is the reason that I had to replace it.
I also measured the voltage in the fusebox ( for the fuse that blows )(this fuse never blows when the engine is not running)and it gave the same as the battery, engine not running.

When I disconnected the brown thick wire onthe alternator the engine didn`t start no power to anything. Then i disconnected the red wire and left the brown on the alternator with the same result. Then I connected the red and brown wire but not attached to the alternator. Now the engine started and the 20A fuse didn`t blow. If I have understood it right this indicate a problem with the alternator. This alternator came from a full overhaul at the workshop, so I contacted them. They wanted to look at the alternator in the car so I have delivered it to them and they promised to do it tomorrow.
Well I hope this will solve my problem but I still believe that theres a serious eletrical dysfunction on this car . And that this problem kills the alternator.

Tomorrow after work I`ll know and I promise to tell you.

There are only two wires connected to the alternator: The 10ga red wire goes to the battery through a fusible link and is HOT at all times. The fuse is fed from the ignition switch when the key is in the RUN position. The fuse feeds the brown wire. From the fuse, the brown wire goes through the filament of the battery icon bulb in the instrument cluster directly to the voltage regulator, which is inside the alternator. The voltage regulator excites the field in the alternator. When the stator and rectifier create output voltage, the alternator starts charging the battery, and the voltage regulator turns off the battery icon. Your voltage readings on both wires are correct; the problem is in the alternator.

Hey again
Well, now I have talked to the workshop an they have found a grounding disorder in the alternator as you expected.
They are going to replace it with a new one over the weekend.
Hopefully this will help me out.
I have to thank you again for the help you have given me.

best regards
JOhn Martin Gylseth

Glad to be of assistance to you. Post back the results so that others following this thread will know what the shop found.

By the way, welcome to the forum!

Thank you
I will post the result from the workshop as soon as I can.

John Martin

Hey
Well now they have replaced the alternator and everything looks allright, but the new alternator is getting real hot to. ( It boiles if I put water on it ) Still the fuse (20A) dosen`t blow. Hopefully the alternator won`t brake down again.

Best regards
John Martin