Here is what the wiring looked like for a 1987 model:
The square box labeled “14” above the “DIGIFANT CONTROL UNIT RELAY” receives battery power via circuit 15 when the ignition switch is turned to the RUN and/or START position—that closes the relay, and sends battery power to the ECU. In 1988, VW changed this relay from a 4-pin to a 5-pin to add a new circuit:
The difference between the two diagrams is the addition of the new circuit, the box labeled “23,” that runs back to the ECU, pin 23. It is a black and white wire:
This is a pin being used on the ECU starting in 1988 that was not being used in any prior year. Per our good friend Craig Forney of Opus, who knows more about these ECUs than anybody else I know, this new circuit probably had something to do with the requirement for all 1988 year-model cars sold in the USA to be fitted with some sort of onboard diagnostic (OBD) system. The requirement was ultimately dropped for the Vanagon, but the modification stuck around until the end of production in 1991.
The 5-pin EFI relay is no longer available (NLA). Luckily, it rarely goes bad—which is one reason we did not bother reproducing it. The other reason is that it is very easy to modify they wiring on later vans to accept either relay in that spot. All you have to do is remove the black/white wire terminal from the harness plug and tape it up (or cut it off), then move black wire terminal to where the black/white wire terminal to the spot where the black/white wire was on that same plug. This simple modification allows for the use of either the 5-pin relay, or the more common 141-951-253B relay, which is the same as the other relay in that black box—that is for the fuel pump.