cold starts
 

96 powerstroke my dad owns has 160,000 miles when it is cold you have to plug it in, trying to figure out what is wrong...we have replaced glow plugs, wiring harness, and relay guys need some help on this....you have to plug it up any temps below 50deg. thanks

sounds like the glowplugs aint workin to me....................on a cold morning after ya cycle them get under the hood and confirm they are warming all 8

check your grounds

Check to make sure that you are getting power to the glow plugs some times the connectors that are in the valve cover gaskets can get hot and corrode and not get power through them and need to be replaced as well seen it many times on the psd so check for 12v through the gaskets at the glow plugs themselves.

Agreed^

my old 96 had to be plugged in as well, the problem was battries. after one year of really cold weather , the battries would not want to start the trcuk unless i had it plugged in.

I replaced everything, nothing worked unless I replaced the battries every year.
so after auto zone finally said no to replacing them for free, I just plugged her in.

Must have been another underlying problem someware. Shouldent have to replace the batteries every year due to glow plugs... When i bought my truck it had a cheep canadian tire 550cca battery that was 7 years old and what looked to be the original ford battery or a extreamly old ford battery. Only reason i changed them as i was having starter problems and thought it was the batteries.

its possible it can be your injector o-rings, I have seen that. Also against all logic, and I mean all logic cause cold oil makes more pressure. My 94, at 180k quit starting below 50. HPOP cured that. Anwser that to me, pumps make more pressure when the fluid is cold, hence why your truck has more oil pressure when its cold. I have no clue how that works. Normally HPOP's cause no hot start.