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Fuel pump relay, which one is it?

posted by  someone claiming to be David Hunter on  Mon May 21 13:19 CST 2001 [RELATED]

I am studying the operation of the fuel pump relay circuit on my 88 740 with LH2.2. Nothing broke just satisfying curiousities. It seems that according to Haynes schematic it has 2 input lines to the coil circuit and is a single relay inside the case. I have always thought the fuel pump relay was the one with 2 relays inside the white case. This is apparently the system relay.

One of the input lines on the single relay goes to the output of the power stage and the other goes to hot side of fuse 12 which receives power when the key is turmed. Am I right to say that when the latter goes to 12 volts this would pick the relay for a timed interval and therby prime the pumps. That would mean the other line holds the relay picked as long as there are ignition pulses prenet from the power stage. If my thought process has not shorted could we then say that if there are no pules from the power stage then fuel pumps would shut down?





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