How do the check relays work

[LavaSurfer]

I'm studying the wiring diagram and I'm trying to grasp how these work since I either have a bad wire or bad relay for my headlights and brake lights because they are always on in the check panel.

I'm looking at the diagrams and it appears the check panel needs to see a ground from the check relay to think everything is working. This of course has to go through the relays that are activated by the + you see from the switch.

My main question is where the ground is coming from to activate the relay for that signal. The diagram indicates to me that it gets its ground through the bulb itself. So does the check panel only need to see a very short ground signal? I am thinking the + signal would just pass right through the coil on its way to the bulb without tripping the relay for the check panel.

[jlevie]

For each of the light circuits monitored by the check panel there is a coil of wire surrounding a reed relay. The current for the light passes through the coil and if sufficient current flow exists the reed relay closes. So anything that reduces current flow through a monitored circuit will trip the warning.