The input circuit of the amplifier is where the radio is feeding power into when the amplifier is keyed. The radio is only attached to the antenna when the amplifier is off.
The amplifier's input circuit should fool the radio into thinking that it's connected to an antenna with a low SWR. The input circuit in this amplifier is throwing the radio a high SWR, triggering the AWI light.
That amplifier model typically has multiple problems. Unless you just want to make a project out of this one, I'd sell it and try your luck again.
It will bring more money before it blows up than it will after.
First problem we're used to seeing from a Gray 200 is the power supply. Your pics don't show it, but it was built with an unregulated power supply. It puts over 20 Volts onto the two expensive 12-Volt RF transistors. Usually causes them to fail prematurely.
There's a bonus. The power transformer it was built with is too small and also tends to overheat and fail if the transistors manage to last for any amount of time.
Maybe yours has an updated power supply. That part of it is not visible in your pics. Can't tell.
But wait, there's more.
Fixing the high input-side SWR that's triggering your warning light will be a project in itself. Requires some rewiring and adding some components.
Unless you bought this amplifier to be a project, I'd recommend finding it a new home.
73
