In short, no there isn't if you want to keep the system standard (won't transfer unless there is space in the main and auto switch off when sub empty).
If you want a "manual system" that you have to monitor and transfer as space/fuel is available then, yes, you can power the transfer pump directly.
I had a manual 'emergency' setup on my Coil Cab (90 litre sub 145 litre main) as I used to do some very remote travel and as we all know the factory system can be a PIA occasionally.
It was setup like a TC lock up system IE in normal the factory system worked, in emergency a relay took control of the pump and fed it 12 volts direct.
You get the sub tank warning lamp in emergency and until you get a chance to disco the battery/ pull the fuses to force a reset but that helps remind you to keep an eye on fuel tank levels
Reply With Quote