hopefully someone can give out some good info on this problem. My truck is an 84 chev. originally had a diesel and got swapped to a small block. im not sure if the truck has the original harness for a diesel or not i am assuming it is. ne ways. the other night after driving i noticed the lights were dim. as i pressed the clutch they got brighter. so i just held my foot on the pedal to take the slack out of the spring and drove it home. i added a new ground cable from the battery to body and frame. i decided to replace the alternator just out of spite. as i started the truck i plugged in the 2 wire connector it bogged the motor down about 300 rpms and charged to 14v. i got in it to go for a test drive, pushed the clutch in and lost charging voltage. What it up with that!!!! ne ways hope some one can help it would b greatly appreciated!!!!!!!!!!!
P.S. is there not supposed to b a wire coming directly off the alternator to the battery or does it charge thru the sire off the starter???

the wire on the back of the alternator can run to the main post on the starter, the junction box, or to the positive post on the battery.
even though you have grounds from the battery to the motor & body, they aren't enough, you also need motor to body grounds too. many times people leave these off when they pull the motor & never hook them back up.
check to see if they are there & in good condition.

Check those grounds as soul hunter said. And it might not be a bad idea to sneak a peek up under the dash around your clutch pedal and linkage, just to make sure there are no wires catching in anything. While your under there look for any ground wires bolted to the bottom or back of the dash, and make sure those are tight as well.
But with your previous issue of dim lights and what you found with the pedal you are probably dealing with ground issues. make sure you have bat - to frame body and engine / engine to body and engine to frame.

well good news. i finally got the problem figured out. after running several continuity checks and voltage checks the brown wire out of the harness had an open in it. i replaced the wire and connector and am currently charging at 14.5 volts!!!!! Thanks for your input and maybe you can help me again sometime!!!!!!!!!!!!