My headlight will not work on my 2000 mercury sable. I have changed the bulb but it just stays real dim then goes out . it is only on the passenger side.

Sounds like you need to look for a bad ground for the passenger headlight.

bad connection or bad earth check all connection or bulb

Mercury Sable - YouTube

? 6:06
www.youtube.com/watch?v=Mlb1V5vNgFM
Jan 3, 2012 - Uploaded by 1A Auto Parts http://www.1aauto.com/1A/HeadLights/Mercury/Sable/1ALHP00223 ... Find out why. Close. How to Install Replace Headlight and Bulb Mercury Sable 00-05 ... How To Install Replace Fog Lightand Bulb 00-03 Mercury Sable

reach behind the headlight and uplug it, rotate the bulb holder ring countgerclockwise pull the holder straight out replace with new bulb. Do not touch the bulb with your bare hand, oil from your hands can cause it to burn more quickly.

Could be a problem with the socket or the switch.
Do you have power and ground on the socket ?

someone has switched the wiring harness sockets to the wrong bulbs or installed the bulbs in reverse. get in behind the headlight assembly on the driver side and reverse the wires, if that does not work then pull the bulbs and swap them inside to outside and vice versa.

once they get to this stage renew the headlights

TEST
remove both bulbs from the lamps but leave them on their wires switch on and see if the bulbs are still different brightness if not they the passenger side lamp housing has damaged mirror is dirty or missalined and needs adjustment. if they are different brightness then this may be a earthing problem.

go here. we can help you. Also, did you check the headlamp relay in the box under the hood? One relay is in box in front of battery, other is in narrow box along passenger side fender under the hood. swap left & rt headlamp relays to see if it changes.

http://groups.yahoo.com/group/villagerquest/

This problem is now resolved, thanks to a prior post by sableowner.

http://www.fixya.com/cars/t1479995-2001_merc_sable_headlight_replacement

The 2003 Sable has the same headlight assembly and removal/replacement instructions as the 2001 Sable. Once I had this information in hand, bulb replacement was easy.