That's a bit of voltage drop there to the glow plug. Remember that the larger a wire you use, the more voltage you're gonna get at the plug. Also, dumb question but how large is your ground wire, and is is connected to clean, paint and coating free metal? I have Saito .56 with a remote glow setup, and at first it wasn't working. The ground wire was attached to apparently clean and uncoated metal, but after working the area with some sandpaper, the system worked just fine.

Andy