Thanks to @An2k, @randomusername, and @edensk for helping!

After some trial and error, I finally figured it out with your help.

I had to use [-clamp(Pitch, -1,0)] as the code, and it finally worked for me.

Again, thanks very much for your help!

this worked on my unfinished project I also use pitch for throttle control
min(sign(Pitch),0)
I wished I remmember where I got it from to give credit.. anyways
my setup Im using both Yaw and Roll for steering BTW..2 beacon light on each side. using codes below for reverse, left and right signal lights
right beaconlight on its input
min(sign(Pitch),0) | clamp(Yaw, 0, 1) | clamp(Roll, 0, 1)
And otherside
left beaconlight on its input
min(sign(Pitch),0) | clamp(Yaw, -1, 0) | clamp(Roll, -1, 0)

when you pitch down to do reverse both left & right signal beacon lights up and lights up when you use Roll or Yaw right/left steering
Edit: guys
@randomusername @edensk @AnOlympicWalnut and everyone else. I need help as well I need recoil using piston to cycle per shot like one cycle (piston default on extended) to retract and extend quick for every -1 ammo fired.. like fullammo = 3000.. fireweapon -1 ammo = 2999 piston will do 1 quick cycle...fire again ammo=2998 another 1 quick cycle then full auto piston sychonized to each shots fired..havent seen any sample project that use ammo counter as a trigger for a piston to sych cycle each shot...is this possible? Its for a high firerate cannon machinegun. Tried using cannon with recoil force but shake my little car into oblivion.Plz Help and suggestion appreciated and properlly credited

@AnOlympicWalnut My bad, I copied her formula without looking at it too much.
-clamp01(-Pitch*100) should work fine

@randomusername @edensk I tried using both suggestions with and without AG, but there were no effects. I have default settings on the light, only the light is resized a bit (if that has any correlation). I'm not using any experimental version of the game either, only normal. Is there anything I have to have set?

Beacon lights apparently activate above 0.5, iirc, so the input should make sure they activate even with the smallest Pitch input.
clamp(Pitch*100, -1,0) should be fine.