Welcome to the forums. Happy to see other mk3 owners out there.
Many things trigger the glow plug light.
You probably just did that work for no reason.
Your car will trigger a glow plug light if the brake lights have a fault lol, among other things it could be.
Scan for codes and stop throwing money at it for no reason (even though you thought you were correct). Gata love VW for misleading stuff like this. Been there. At least you have new glow plugs for winter!
your car (so is mine) has many things that will cause it to not start, and the 109 relay is one of those things that does not throw a CEL (maybe it does, I’ve been told now that it should but my 98 Jetta never once threw a CEL over the 109 relay issue.) there is a good thread around here for no start troubleshooting, you should read through it. Can't find the link right now but you can do a search easily.
You’re not a crazy distance from me. I am parting out my Jetta and wanted you to know I have some goodies you might be interested in, nothing engine related though.
Listing is here with pictures (CLICK ME)
As for your harness, that sucker gets really brittle, there is a good chance you have damaged it, it’s so freaking easy to do when you change out the GP or go injector work. You can wire them up temporarily; it’s just a connection at the top of each one so in a pinch you can rig it up if the harness is fubar.
Scan the car first. Have someone check your rear lights as well. there is a harness in the trunk under the carpet right by the latch area, if it gets wet, this will give you nightmares on tracking down the issue of why the lights work and done work, food for thought, dove me nuts for weeks trying to figure that one out. Anyways, send me a message if you’re interested in parts or just have general questions.