[03f250stroke]

on my 03 which i think is the same as your 04 should be a bar harness..its like hard squared plastic i believe. you need to work it at each end and then work in between each glow plug. its tricky but it comes off sorta easy after you get it off

btw the glow plugs come out with a 10mm deep socket..the 1/4 socket fits in there good

 

[03f250stroke]

they are held on kinda like a spark plug. on the 03 that plastic harness is prone to cracking. so you should have a a real problem putting a little force on there, use a small pry bar and work each plug then.