You can just run a constant power wire from the battery to the cig lighter and it can be constant... the one that goes to it is switched so just replace that with a constant and you should be good to go...

Haven't tried this but in theory it should work... You can either go directly from the battery or find a constant power wire that would support the load of whatever you plug in to the cig lighter.. I would just run a separate power wire directly from the battery though... with a fuse of course... that way you have a separate circuit and nothing else would be effected if that fuse blew.

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'98 E300 Turbo "Juliette"
'85 Federal 300TD