Voltage

"John Q Public" wrote in message news: snipped-for-privacy@4ax.com...

Your alt is bad (even if the battery was bad once the engine started the alt would produce 13+ volts) just get another alt and change it. Be sure to unhook the battery before you do anything that red lead at the back carries battery voltage and will give you a very sizeable spark if it touches anything (been there done that). When you pull the old one you will see a set of numbers stamped on it (I.e. 12v 100amp) make sure the new one is the same amp or larger (must be same physically size). Two bolts hold it on and a large wrench on the belt adjuster pulley (bolt will be in the center of the pulley) that has the spring will allow you to move the pulley up and take off the belt. Make sure you do charge the battery before you hook up the new alt a sudden heavy load on the new alt can burn it out quickly. The alt will come with an instruction sheet that will tell you which battery cable to hook up first. You may also want to take the opportunity to change the belt at the same time since you already have it off. Easy should take you 15 min to change it. You are looking for a output voltage of ~13.7 volts to a max of 14.5 from the new alt. You can use the dash volt gauge or if you have one, a hand held volt meter to test all voltages. I get my parts from pep boys with lifetime guarantees (I keep my cars for a min of 20 yrs) so call around. The alt is one unit everything is internal gone are the days of a firewall mounted voltage regulator... Basically the alt has a plug that has two leads (black and brown I think) on it, one sends power to the volt gauge (or light) and the other brings power back from the gauge (or light) so the internal regulator senses the volt difference (resistance) of the gauge (or light) and compares it to the battery voltage (large red lead at rear) and charge output amperage is based on this number. In most cases it will be a bad alt but can be (in very few cases) a bad gauge or instrument cluster connection. Sometimes the plug at the top of the alt will corrode and loose connection which confuses the alt and it will full field and send full power to the battery cooking it. Best way to fix this is to clean the contacts on the plug or change it with a new one. More information then you needed but it should be an easy fix.

good luck, mark

Good exp. Merk

Check your battery connections, for corosion and tightness. The GM alternators use Avalanche diodes that do not like current surges from a sparking contact. One of the main reasons that the alternator goes, unless you have a bad voltage regulator.

Cheers

MARK, great play by play. This is a big help.

It was the alt. Cost me about $130. I swaped it in about hour.

PS: Thanks to all who posted.

Thanks JQP