Modern trucks are EBS now , as failsafe for yellow line failure.
Measuring truck applied brake position and relaying to the EBS/ ABS module on the trailer electronically through ISO and ABS line and comparing it with the yellow line pressure into the trailer control valve so if truck applied pressure is substantially higher than that being fed into the valve from the yellow line it will electronically apply the brakes to match those of the truck by diverting the stored air from the trailer tanks through the valve to apply the brakes .
Clever stuff.
Need to look out my Wabco notes , been a while .
Measuring truck applied brake position and relaying to the EBS/ ABS module on the trailer electronically through ISO and ABS line and comparing it with the yellow line pressure into the trailer control valve so if truck applied pressure is substantially higher than that being fed into the valve from the yellow line it will electronically apply the brakes to match those of the truck by diverting the stored air from the trailer tanks through the valve to apply the brakes .
Clever stuff.
Need to look out my Wabco notes , been a while .