1992 Chevrolet S-10 Undercharging

what kind of volts it's putting out first it should be about 14.5 maximum. check ign/gauge fuse in fuse block see if it's ok. also check condition of battery including load test. Auto parts does for free

I did not check voltage before it was undercharging , but the instrument voltmeter showed above 13 volts and all the things were good until a weak battery light came up soon and voltage dropped below 12 .

I assumed the reason was the rectifier which was not changed , so went to replace that also , but nothing happened .

Checked the voltage with the engine running and it was 11.70 volts .
All the fuses are ok .
Tested alternator with another battery , same issue .

The strange thing that I noticed today is the weak and flashy battery check light , was there with both switch on > engine off and with engine on !

Because with switch on > engine off situation , there is a path to ground through regulator . it means that something is wrong with regulator again .

In cs - 130 manual , I read if there is a problem with the armature like open some were in it's windings , it can damage the regulator .

check the fusible links I have pointed out in pic not the 4amp fuse. then make sure you have agood ground going to engine block from battery , same to body and same engine to body usually a ground strap back of block to firewall. I don't think it's an alternator problem. I think one or more of your fusible lnks are bad and not giving alternator the power to make it charge.

Thanks a lot for your responses.

Problem solved and again it was a faulty regulator . Despite it was new , but as soon as working for some seconds , it went bad . The circuit inside it , did not allow ground to reach instrument battery light when ign switch was on and so on when engine was running , there was not enough ground for the alternator to work properly .