The idea here is to introduce a relay into the starting circuit to lessen the chances of your bus not starting when it's hot. Picture the path the current from the battery must take to start your bus: From the battery all the way up to the fuse box, through the ignition switch, and all the way back to the solenoid. You've got 20 yr old wires, dirty corroded connections, and a hot solenoid, ensuring that you definitely won't get enough juice to start the car. By adding a relay into the circuit, we are improving that electrical path.
Supplies needed: 1 Bosch WR-1 low-voltage relay kit. This is a relay made specifically for this purpose and comes with the wiring already made up with the right connectors. It also comes with a 15-amp fuse for the relay.
OK, here's what you do:
1) DISCONNECT THE BATTERY. Don't screw around with your starter with the battery connected. Death or serious injury follows when you accidentally short the connections and the starter cranks the bus which you left in gear and it promptly runs you over because you're laying right in front of the wheel.
2) You may want to jack up the bus a little, might help you reach. Look on your starter. You will see one of the post connectors, terminal 30, has a bunch of wires going to it, big fat ones. This post gives you your direct connection to the battery. Take the 13mm nut off the post and put the appropriate wire from the relay kit there. The relay kit comes with good instructions as to which wire is supposed to go where. This wire will have a push-on terminal on one end and a ring connector on the other.
3) Put the 13mm nut back on terminal 30, you're done there. Now, pull the wire from the ignition switch off of the solenoid. Fuel injected buses have two wires up there, the Idiot book has a nice picture of which one is ignition and which is fuel injection. I think the thicker one is ignition, but I won't swear to it. Anyway, take the ignition switch wire off and put it on the relay terminal for switch current. this is what will activate the relay.
4) Hook up the wire that goes from the relay to the ignition switch terminal on the solenoid (again referring to the relay instructions. This one will have a push-on connector on each end.
5) Mount the relay somewhere convenient. I mounted mine to one of the long screws that you find at the rear of the starter. Mount it with the terminals facing down so that water will have a place to go and not collect inside the relay.
6) Now you have to hook up one more wire, the ground. This one will have a ring connector on one end and a push-on on the other end. Ground it to any bare metal area within reach. I seem to recall grounding mine under the same starter screw that I mounted it with.
6) Check every now and then to make sure your connections stay corrosion free and all that.
The Bosch relay comes with a 15-amp blade-type fuse mounted to the relay. If you turn the key and nothing happens, check this fuse as you might have blown it. If the fuse is blown, that means your solenoid itself needs attention. The solenoid is sticking and is drawing much more current than it should be to get going. Do not replace the fuse with a higher amperage fuse. Bite the bullet and get the solenoid replaced. It's a good idea to also keep a couple of these blade-type 15-amp fuses as spares in the glovebox, since nowhere else on the Bus are blade-type fuses used.
OK, here's what you did. Picture the flow of the electricity now: You've taken the wire from the ignition switch that used to trip the solenoid off the solenoid and are now using that 12v signal to trip the relay. Even if there is a voltage drop you are still likely to have enough juice to trip the relay. Then you hooked up a wire to the big post on the starter, which is power directly from the battery about a foot away. Then you hooked another wire from the relay to the ignition switch terminal on the solenoid. Now instead of getting your power to the solenoid by way of Outer Mongolia, it's going directly from the battery to the solenoid, enabling you to get all the juice you need right to the solenoid. Now the ignition switch current only acts as a signal to tell the relay to send the power to the solenoid. As a side bonus this may help your ignition switch last longer as there will be much less electrical load on it.
OK, those are my instructions above. Now here are the instructions that come with the Bosch WR-1 kit. They were sent to me by Jeff Stewart and credit for the scans goes to Barry Burneskis. These should help clarify the process with the appropriate connections to the Bosch relay.
Click here for the installation diagram.
Click here for the written instructions.