My fuel shutoff sol stopped pulling in I ordered new ones (4) and they all do the same.
my schematic only shows a ground and one wire from the relay in the dash.
when I turn on the key it does not pull in. so in research I find I need a constant 12 vdc from another source.
If anyone has or knows where I can get a schematic to show me where both the red and white wires get the 12VDC from please direct me.
I have a work around but want to fix soon
Also where can I get complete as built schematics for my 1994 U280?
There are 3 wires for the solenoid. Ground, pullin winding and hold in winding.
The holdin winding gets its power from the ignition and the pull in winding get
its power from the starter circuit so when you first engage the starter the solenoid
is pulled in and it won't release until the ignition is turned off.
On my previous 1994 Bluebird BMC with a mechanical 8.3, there was a secondary constant duty solonoid under the rear hatch that fed power to the fuel solonoid. I had to replace that once with same symptons you have.
Can you trace the wires from the fuel solonoid?
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Expanding on Peter's (oldguy) comments, the 3 wires going to the fuel shutoff solenoid are:
WHITE (pull-in or suck-in winding)
RED (hold-in winding)
BLACK (ground)
The WHITE wire is a high amp draw circuit (20-30 amps, momentary duty, only when starter motor is engaged)
The RED wire is a low amp draw circuit (about 1 amp, continuous duty, as long as ignition switch is ON)
Studying the B-2037 U280 12V Wiring Diagram, we can deduce that the hold-in circuit (RED wire) is powered directly off the small "activation" post on the IGN SOL (located under the lift-up dash cover on U280). This "activation" post is HOT as long as the ignition switch is in the ON position. The fuel shutoff solenoid BLACK ground wire is also shown on this diagram.
As you have observed, the B-2037 Wiring Diagram does not indicate the power source for the WHITE wire - or at least I connot find it. The diagram linked below (Cummins Marine Fuel Shutoff Solenoid Wiring) shows the WHITE wire being powered off the "downstream" (non-battery) side of the F496 relay. The F496 relay corresponds to the AUX START SOL on the U280 C8.3 (see the B-2126 U280 Automotive Wiring Diagram). This power source makes perfect sense because the "S" post on the AUX START SOL is only hot when the ignition switch is in the START position.
I believe the "S" post on the AUX START SOL is the most logical source for power to the WHITE wire on the fuel shutoff solenoid. I have no idea why this circuit is not shown on the FOT wiring diagrams.
NOTE: Since I have never actually traced the fuel shutoff solenoid power supply wires on my coach, everything I have stated above is OPINION based on my interpretation of the diagrams. TIFWIW.
Fuel Shutoff Solenoid Wiring 101 - Seaboard Marine (https://www.sbmar.com/articles/fuel-shutoff-solenoid-wiring-101/)