Lorry, 4-ton, APF and Lorry, 4-ton, ZPI - Details needed

[Lynn Eades]

Did those trailers have electric brakes, that required the trucks to be fitted out for the trailers?
I was an apprentice mechanic in the early 70s. My unit was an LAD and as such we looked after an Artillery unit that used 5.5 guns. These guns had electric brakes. The gun tractors were Australian built Mk5 International 6x6s.
They were fitted with a large hand operated rheostat to activate the gun brakes. They were not connected at all to the foot brakes of the trucks. Anyhow I digress. You radar trailers would have been quite heavy leading me to think about this possibility.