SECURITY LIGHT 1998 CHVY Z71

TRUCK WAS RUNNING FINE. ONE MORNING I GO TO
START IT , IT WLD CRANK BUT WLDNT START. TRIED A
FEW MORE TIMES..NOTHING. I ACCIDENTALLY LEFT
HEADLIGHTS ON BEFORE I WENT INSIDE AND LAID
BACK DOWN. (was gna try again later with the truck).

After realizing wat i had done, now ever since then
when i put in my key and turn it to (any poistion) to on,
(after my gauges do the bulb check), MY SECURITY
LIGHT STAYS ILLUMINATED.  

Ive already tried, 10mins X3 , 11 x3 procedures,
unhooking the battery for a cpl hours, checked fuses
and relays, my fuel pump has power and hums wen i
turn the key over.. etc etc... THE ONE THING IS THAT .Y
SECURITY LIGHT STAYS ILLUMINATED BUTTTT IT
NEVER FLASHES OR GOES OFF....NOT AFTER 10MNS
11MNS 30MNS NOTHIN..

one more thing
..ever since...if i wanna get out there n try tk solve thks
problem then i have to have jumper cables to give my
battery power, but once i remove the cables it soon
lpses power again...IVE HAD THE BATT TESTED,
GOOD. THE ALT TESTED, GOOD.

NEW BATT? NEW KEY? KEY CYCLINDER? PCM?
I HONESTLY THINK IF I CLD RESET MY ANTI THEFT
SECURITY THRU A COMPUTER WLD THAT FIX IT...?
IDK


APPRECIATE THE TIME AND ANY HELP OR IDEAS OF
WHAT TO TRY OR ROUTES TO TAKE.