How do I add a rear light to my Altas S-1/ S-3

[vande]

I'm confounded by what seems to be a simple modification to my Atlas built Alco S-1/S-3. I want to add a headlight to the rear of the switcher. It's fine with me that both lights will operate simultaneously. I've tried soldering a 14 V grain of sand bulb (with a resistor that brings the voltage to 1.5V) to the leads on the terminal strip. The bulb does not illuminate. If I disconnect the terminal strip screw and thus disengage the motor, both bulbs illuminate. Can anyone help this electrically challenged model railroder? Thanks if you have any advice.