A similar system in the Haynes manual for the Dolomite shows they are all junctions and each symbol gives the location of the junction.
In this example a circle in a circle is a column junction, diagonal line is the facia, cross is body, horizontal line gearbox,cross with top and bottom section blacked out is hazard switch.
Not sure these match your drawing application are you sure there is not a key on another page or diagram. Haynes Morris Marina manual uses same system but sadly no key on any drawings there either.