That sounds a really nice simple fix, but think logically about it and it will make the situation much, much worse.
As I understand the posts here, this plane has several sensors/circuits that take part in the ground/air mode decision. So which one do you choose to light up your big frickin light? Only part of the plane thought it was in air mode, the rest was still on the ground. Put in your light and choose the wrong circuit to drive it and you make the whole thing many times worse.
Yeah,
At the very least, the light needs to tap on all sensors and indicate:
-Ground
-Air
-Disagree
-Off (light broken)
Unfortunately, if i.e. the Madrid case turns out to be a case of a malfunctioning single relay (R2-5), even if you make this more sophisticated logic, as you just mentioned, it will still confuse the heck out of the pilots ...
They will see an indicator lighted:
-Ground
Then, if they notice at all, they'll see a RAT probe indicating way too high temperature. Maybe they'll notice/figure the heater is on.
Maintenance will see the logic is "correct", so it must be a case of the heater "mysteriously" malfunctioning. Cut it out, MEL the thing, and out we go.
And we still get Madrid's likely inop TOWS takeoff condition ...
Boeing's recommendation of testing TOWS shortly before each take off is the best (and cheapest, mind you) solution. The alarm could still fail from the time it was tested til the time it was actually needed, but usually that would be some short period of taxiing time, so the risk is small.
Testing with a POSITIVE test, where you actually hear the alarm, not a test where you are suppossed to NOT hear the alarms, which is "worthless" in case of a "broken" TOWS.
The real "best solution" is a TOWS re-design where the alarm indicates both, possitive and negative results. Nowadays, with digital technology, I'm sure the change wouldn't cost all that much (at all). You push the handles and the TOWS will announce out-loud:
-Configuration OK (you are good to go)
or
-Beep - slats -- beep -- flaps (you are not yourself today -- drink more coffee and stop chatting on your cellphone with that cute flight attendant you are about to meet)
or
-Silence (TOWS is inop ... you are NOGO)