If your Vanagon does not crank when you turn the key, it is one of these items:
1) Dead battery or no connection between battery and starter.
2) Bad neutral safety switch (automatic trans only)
3) Bad ignition switch
4) Bad wiring or connection between the ignition switch and starter
5) Bad starter
1) First and foremost, make absolutely sure your battery is fully charged before proceeding. If in doubt, have your battery checked to see if it's holding a charge, and make sure that both ends of the big fat wire running between the battery and starter are clean and tight. Make absolutely sure you have good connections and a fully charged battery, and that for sure there is a solid 12VDC present at the big post on the starter. Also, make absolutely sure the ground strap between the battery and body is tight and clean at both ends. There is also a ground strap between the transaxle and the chassis, at the front of the transaxle. Make sure it is clean and tight. Failure to do this will waste a lot of time, and make you feel very frustrated.
The SECONDARY electrical circuit that operates the starter (circuit #50) is a bit more involved, but still pretty simple. The starter is actually an assembly that includes an electric motor and solenoid. The secondary starter circuit sends power to the solenoid, which in turn connects the primary electrical circuit to the electric motor itself, internally within the solenoid. On the backside of the ignition switch there is a white plug with five or six wires. The fattest of the wires is a solid red wire that is always hot with 12VDC (circuit #30), and leads back to the battery positive post. There is another wire the same gauge as the red one, which is red with a black stripe (circuit #50). This wire eventually ends up at the solenoid on the starter assembly. When you turn the ignition switch to “START," the ignition switch connects these two wires and sends power to the solenoid on the starter, which sends power to the starter motor (internally) and cranks the engine over. If your vehicle has an automatic transmission, there is an “interrupting” switch involved, called a “neutral safety switch” located on the shifter itself. It is there so that the engine cannot be cranked unless the shifter is in P or N.
To check circuit 50:
2) If your Vanagon has an automatic transmission, the red wire with the black stripe has to pass through the neutral safety switch contacts that are located on the shifter itself. With your LEFT hand, turn the ignition switch to the START position and hold it in that position. With your RIGHT hand, move the shifter from P to N, and back to P. CAUTION! The vehicle may lurch during this test. Make sure the parking brake is set, and there is nothing and nobody in front of, or behind vehicle. If the engine cranks or starts to crank, the problem is in the neutral safety switch. Take the shifter apart and clean the contacts. For testing purposes, these contacts can be bypassed. If it fixes the problem, clean or replace the switch parts. And if doing so still does not fix the no-crank issue, the problem is clearly NOT with these contacts, and you can continue as follows:
3) Now let’s check the ignition switch. For this step, you will need a new ignition switch. These are not expensive, and it does not hurt to carry a spare. Next time it does not crank, remove the lower half of the steering column plastic cover, two screws, very simple. You will see a group of about six wires going into a white plastic plug that plugs into the back of the ignition switch. Unplug the group of wires from the ignition switch (don’t worry, it only goes back on one way). Plug the new ignition switch into the electrical plug just removed. Using a flat bladed screwdriver, operate the new ignition switch. If the engine cranks over, it is the ignition switch that is the problem. If it does not, it is either the wiring between the ignition switch and the starter, or indeed the starter itself.
4) To figure out if it is the starter itself, it is just a matter of jumping power between the big fat post on the starter motor with the smaller electrical contact on the solenoid. For this step, you will need a remote starter switch. CAUTION! The engine may turn over during this test. Make sure the parking brake is set, the vehicle is in park or neutral, and there is nothing and nobody anywhere near engine V-belts. If you jumper the big fat post on the solenoid to the small terminal on the solenoid—with a fully charged battery and known clean connections—and the engine does not crank, the starter is for sure dead. If it cranks normally, there is a wiring problem in the vehicle on circuit #50 (fat red wire with black stripe) somewhere between the ignition switch and starter solenoid, probably one of the plug connections along the way.