Lift Pump Voltage

[DBar]

Hi All

98.5 24V 3500 worked fine two nights ago. Next day when I started it, was running rough. Checked the Fuel Pressure Gauge and was reading Zero. Shut down truck and cycled key to listen for Lift Pump (Relocated to chassis with Vulcan's Kit last year). No go. Won't cycle at all for 3 secs after turning key on, or for 25 secs after bumping starter. Connected small 12 volt battery directly to lift pump on chassis and away it went pumping fuel as it should. Disconnected small battery after a few seconds after fuel was pushed to filter and truck started and ran OK - but lift pump still not running with vehicle supplied voltage. Checked voltage at pump and got 7 volts when key turned to on, but not to start. However this may have been intermittent, hard to tell as the meter probes were a little big for the pin holes.

Any ideas on what could be going? I've pretty well ruled out the lift pump, as both the new one and the old one (which I removed last year) work fine with the 12 v battery, but neither work off the vehicle harness.

Thanks for any info guys. I've read for a long while and have used a lot of the info from this site, but haven't had to write in before.