The wiring on a VW van or bus can be very simple. This is particularly true of older models (mid 1960's and earlier).In fact it's probably one of the simplest wiring schemes in automotive electronics.
For example, there is one wire leading to each set of bulbs in the tail lights. Each one of the bulbs has two leads, one to one of these wires and one to ground. Electrically speaking, very simple. Practically as well. There is no way to achieve the same effect
with fewer wires.
There is one wire running to the left and right set of brake lights, one wire running to the left and right set of turn signal lights and one wire running to the back up lights. It doesn't get much simpler.
A word about the ground wires. As in all cases of ground wires, they must connect to completely bare, bright, shiny metal. After the connection is made, then and only then joint with grease.
After making a ground connection, you can protect the joint from moisture, dirt and general crud by slathering the joint with grease. You don't need a bunch, just cover the whole area and the connector.
The grease trick is especially important if the joint carries a lot of current or one side of the connection is a metal that corrodes. Usually if the wire looks like it's bigger than the average wire, it carries a lot of current and is a good candidate for a really good connection followed by grease.
Generally, anywhere on the body is metal that corrodes (in this case, rusts) On old VWs, there are virtually no semiconductors to worry about. The early fuel injection computers are an exception to this rule.
They became available in the late 60's. A factoid that I can't get over is that the lowly VW was the world's first production car to offer EFI (Electronic Fuel Injection) as standard equipment.
As long as your only concern is on a non-EFI VW bus, you're all set.
Find more repair tips on vintage VW vans and also locating VW bug parts.