1982 Porsche 930 turbo will not start

[Antoine930]

my 1982 Porsche 930 turbo euro. version all of a sudden it cranks but would not start.
I was able to start it only after bridging the primary and secondary pumps.
but then again it will not turn off after turning the ignition off.
all fuses and relays are good. but somehow no power goes to the pumps until the relays are bridged.
any help is greatly appreciated.

[john walker's workshop]

Check the over boost relay and cut-off switch. White wire on the switch comes off sometimes. Try grounding the wire for test purposes. The yellow relay on the engine panel can fail or lose contact with it's plug.