Letter designations on headlight switch?

[PT81PlymouthPickup]

Does anyone know what the letters D, H, B, A, R, stand for on this headlight switch? Original switch, out of my 39 Plymouth PT81 truck.

 

I figure B is for battery, but not sure about the rest?

[Merle Coggins]

According to the wire diagram for my B-Series truck, B is the Battery connection, which is where the circuit breaker connects. H goes to the Headlights. A goes to the front parking lights. R goes to the tail light(Rear?). And D goes to the instruments (Dash) lights. 

[PT81PlymouthPickup]

2 hours ago, Merle Coggins said:

According to the wire diagram for my B-Series truck, B is the Battery connection, which is where the circuit breaker connects. H goes to the Headlights. A goes to the front parking lights. R goes to the tail light(Rear?). And D goes to the instruments (Dash) lights. 

Thanks Merle!  Very helpful. I suspect my earlier switch has the same designations. Perhaps A meant auxiliary?