Glow plugs aren't bad to do. The problem is most likely uvch. (under valve cover harness)
Wires go from the main harness to the valve cover gaskets (plastic with a connector on it) to a short harness inside. The glow plugs draw a lot of amps + it melts the connections after a (long) while. You can get the main harness terminal ends from Ford also. For parts-terminal ends (4) uvch (4) valve cover gaskets (2) glow plugs (
you're looking at maybe $200-$250. I did the whole shooting match on mine.