I recently had the situation where the glow plug light would not come on with the ignitition key but the car started, although roughly. I had all of the glow plugs changed. I bought the car with 97,000 miles and had 106,000 at the time.

I added a wiring harness in my trunk for a trailer and left the ignition in the on position without starting the car while connecting this wiring. Now, the dash light does not come on and I can start the car (roughly). The light comes on after a minute and then goes out after another minute or so.

Did I cause the glow plugs to fail by leaving the ignition on without the car running or is this unrelated? Or, could the wiring to the back tail light harnesses for my trailer connection have caused this? I didn't remove the harness to test this notion. Any suggestions or help would be appreciated as it cost me $450 to have the glow plugs changed a few months ago.