97 ram 24v

2nd generation. I am stumped with my issue. It wouldn't crank, so I turn the
key on and jump at the starter and it fires right off. As I drive off a few miles
later the speedo quits, then the power windows have no power, so as I drive
across Pa. in the rain with the windows down, I notice the MPG reading in
the head liner drops from the normal 17.5, when I get home the gauge reads
7.2 MPG.  However the engine seems to run normally with normal MPG. I
have power to both side of all fusees as they should. My only guess is the
aftermarket safety 'anti thief' deal. It usually has a red blinking light, there is
no light now. As I trace the wires back under the dash , they all disappear
into a shrieked wrapped gizmo, about the size of a typical 4 prong solenoid,
which seems to be self contained.  Got any advise???   Thanks  Gene