LOSS OF EQUIP COOLING CAUSES A CHAIN REACTION.

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AT CRUISE ALT ATL-IAH WE GOT EQUIP COOLING LIGHT; WENT TO ALTERNATE AND TRIED SEVERAL TIMES BACK TO NORMAL BUT GOT LIGHT BACK; RETURNED TO ALTERNATE AND KEPT IT THERE. MINS LATER GOT DUAL DC FAIL LIGHT ON IRS. CALLED MAINT CTL. AS WE WERE TALKING TO MAINT CTL; BATTERY BUS SHOWED NEGATIVE AND THE BATTERY WAS DISCHARGING. GENERATORS WERE NORMAL. ANTI-SKID LIGHT CAME ON. WE ASKED MAINT IF WE SHOULD PULL BATTERY CHARGER CIRCUIT BREAKER. THEY SAID 'YES;' WE PULLED IT. THEN WE LOST N1 AND EGT'S; (BOTH ENGS). AS WE WERE TALKING; WE LOST COM #2. WX AT MSY AND WX BTWN US AND LFT; WE DECIDED TO CONTINUE TO IAH. WE THEN LOST CAPT'S ADI AND HSI. SWITCHED HIS TO #2. TRIED TO SWITCH ATTITUDE BUT LOST AUTOPLT. WE WENT BACK TO NORMAL TO KEEP AUTOPLT. WE WENT TO FLT MANUAL TO SEE WHAT WE HAD OR HAD LOST. WE THEN GOT REVERSER LIGHTS; RED GEAR LIGHTS AND ELEVATOR FEEL LIGHT. WE TRIED TO CALL FLT ATTENDANTS BUT THE CALL BUTTON AND PA DIDN'T WORK. WE DECLARED EMER. I FLEW ON AUTOPLT TO 2000 FT AND THEN HAND FLEW IT. ON LONG FINAL I WENT BACK IN CABIN TO VERIFY GEAR LIGHTS. I MADE NORMAL LNDG. AS WE TAXIED OFF RWY; WE SMELLED SMOKE. CAPT HAD ME GET OUT OF MY SEAT AND OPEN CABIN DOOR SINCE THE SWITCH DIDN'T WORK. WE SAW THICK SMOKE IN CABIN. CAPT GAVE ORDER TO 'EASY VECTOR' OUT L1; L2 AND R2. NOBODY WAS HURT. THE SMOKE WAS DUE TO PACKS OVERHEATING.