Life-Like GP38-2 locomotives have an additional lamp added for the number boards which, as wired, causes problems on DCC (it does not adversely affect DC operation).  Since the bulb is wired to the gray (negative motor) pin and the black (track pickup) pin, your DCC system will see this as a short circuit.  Disconnect the bulb from both pins and wire it to one of the function leads on the decoder to solve this problem.