computer problems?

[formerlylifted]

I have a 2005 GMC Sierra 4x4 W/T w/ 4.8. Ok, it's a base truck model, no power windows or locks, vinyl floor, no security system, am/fm radio was swapped for aftermarket Rockford-Fosgate deck, 305/70/17 tires, with no other mods. The heater/blower motor resistor has been replaced along with the wiring harness but I dont think it would have anything to do with this. My problems are that my alternator/volt guage would show about 13-14 at startup and would drop to about 11-12 after driving about 30 miles. When it would drop, my stereo would dim and cycle off and on as if it were lacking power, turn the volume down and it works again. Now, my guage zeroes about 1/2" past the high redline and pegs to the bottom right edge of the guage. Another problem is that the security light blinks on and off every now-and-then. No check engine light and no problem codes could be retrieved. Can someone tell me what could be causing these problems? Thanks in advance.

[unsolved]

Have your alternator tested. Most likely the culprit.

[bobcat5544]

I have a 2005 GMC Sierra 4x4 W/T w/ 4.8. Ok, it's a base truck model, no power windows or locks, vinyl floor, no security system, am/fm radio was swapped for aftermarket Rockford-Fosgate deck, 305/70/17 tires, with no other mods. The heater/blower motor resistor has been replaced along with the wiring harness but I dont think it would have anything to do with this. My problems are that my alternator/volt guage would show about 13-14 at startup and would drop to about 11-12 after driving about 30 miles. When it would drop, my stereo would dim and cycle off and on as if it were lacking power, turn the volume down and it works again. Now, my guage zeroes about 1/2" past the high redline and pegs to the bottom right edge of the guage. Another problem is that the security light blinks on and off every now-and-then. No check engine light and no problem codes could be retrieved. Can someone tell me what could be causing these problems? Thanks in advance.

 

IF IT IS NOT THE ALTERNATOR

 

FROM WHAT YOU POSTED IT SOUND LIKE SOMEONE SPLICED THE RADIO HARNESS INTO THE IGNITION WIRE HARNESS AND NOW THE RADIO IS CAUSING A HIGH POWER DRAW WHEN THE RADIO IS TURNED UP.