Wires, wires, wires. One of the two fuses on the relay board. The ECU. The connections between the various wiring harnesses and the relay board. The relay board itself...
Brad Anders has a troubleshooting flowchart on his D-jet website,
http://members.rennlist.com/pbanders . Bill Williams wrote up a procedure earlier about the fuel pump control system; this procedure is up on Tim Jones' 914 Fan site.
http://www.914fan.net/fuelpump.html
--DD