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Do other things that only work with the ignition on still work (like dash HVAC fan)?
If no, the ignition solenoid is a likely suspect.
If other things work, check BOTH fuses to the Allison ECU.
Does the Allison shift pad light up? If so, have you used the up/down arrows to check for diagnostic codes? It is easy to do from the driver's seat with no tools and is well described in your Allison owners manual. If that is not available, also on Allison's website or we can give instructions.
Dianne and Brett Wolfe
1997 Safari Sahara 3540
Moderator, FMCA.com Forums
Chairman, FMCA Technical Advisory Committee
Member, FMCA Long-Range and Development Committee 2007-2009
Moderator, http://www.dieselrvclub.org/(FMCA chapter)