....if your system is correct, you do not need a full time source of power to the glow plug.
In fact....when the battery power is applied to the plug, it results in a much hotter plug than
what it is normally. This can throw off your tuning, as well as have negative results....such
as detonation and overheating.

The system you have is fine, but use a switch so that it is only "on" at 1/4 throttle and less,
not all the time.

FBD.