My stock 2003 Chevy Blazer has a 100 amp alternator in it and since it was new if all electrical was on and then add the brake lights it would start to drop from 14 volt to about 12 while in gear and at a stop.Is this normal or should I increase the amperage of the alternator anyone got a answer for me how about it Captain what do you think there is no shorts or corroded cables just seems to be more demand then supply.

 

My opinion is that the stock 100amp alternator is adequate and the one in your Blazer is not able to provide rated full load output. Have you ever taken the alternator to a shop and have it tested?

 

johnnylovsey, where are you located? If you're close to central VA, I have an extra stock alternator you can have. Just the bearings make a little noise sometimes at startup but it functions fine.

 

The gauges in these things are known to not be the most accurate things in the world. I would test the voltage directly at the alt with a DMM

 

Yes I have had it tested as well a tested it myself with a volt meter and idling with a full load everything on it drops to about 12.50 then without the max load it returns to 14.15 and has been that way since the day I purchased it and replaced the old one.

 

But its just the drop that bothers me is 12.50 to low when everything in the car is on ?

 

Probably an issue with the voltage regulator's bridge rectifiers.
Install an AD244 alternator, then you wont have that issue anymore.

 

I had a similar issue, I upgraded to a DR44G and my voltage only drops to 13.5 at idle when my efans are running and my sub is going.

 

So I purchased another 100 amp stock alternator with every thing on full load it did the same thing as the older one.So took your advice sorta Tajohns returned the 100 amp got a 145 amp lifetime alternator there were a few differences the regulator plug was at 12 o clock not 2 o clock but it still reached then the alternator base was larger so my stock belt wouldn't reach any more.95750 outside diameter so we replaced it with a 96580 it worked out awesome at full load every thing on in gear brake lights too its now putting out 13.5.Oh yea that vacuum noise I was hearing after replacing my intake manifold gaskets turned out to be the evap control purge valve line from the throttle body wasn't plugged on all the way off just enough to make a air hissing noise that couldn't be found with soapy water just by luck when working with the alternator I noticed the plug not on fully and could make a difference in the air noise with my finger at the connection.

 

The AD244 / DR44G has a larger housing and requires a 1" longer belt.