Proto 2000 FA2 some Dcc Help please

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Just bought a proto 2000 FA2 { the one with the working fan unit }
i am going to Dcc this unit if at all possible
my problem is as follows , loco arrived , un boxed it and put it on test track , to my horror it began to smoke .
removed from test track , and removed the cover , to find somebody has really messed up the wiring
so i removed the bad wiring and here is what i am left with { pic attached }
the two black wires up top are from both Trucks { i have solderd them together as i belive this is needed for decoder }
Then there is a Red wire from the top of the motor
Then another Red wire from the bottom of the motor
and lastly a Blue wire coming from the chassis
The Black & Red wire sticking up from the right are coming from the led bulb

if anybody could tell me the correct way to add a decoder i would be grateful
also on this loco is there a problem isolating the wire underneath the motor ?

Thank you in Advance
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