Basic Lighting Help Needed

Is the engine area clear? Are there portholes? An "exhaust" area?

If it's solid, there may be no way to do this easily. You can try vacu-forming the parts, but you'll loose detail. If it's just the exhaust, vacu-form the part in clear acetate, then spray dullcoat over it.

In the engine compartment you'll now place a red Light Emitting Diode (LED). Solder lead wires and attach them to a battery pack, runnng the wire down the stand. Repeat for any additional engines. To get fancy, you can add a flashing LED which will simulate a pulse.

Radio Shack will have all you need. LEDs are good to use because of their long liife and no heat build up.

Like aj, I would recommend you going with one or more LEDs, and would look at using some roughed up clear plastic to diffuse the light.  You'll need to remember to put a resistor into the circuit so you don't fry the LED.

As to designing the circuit, Starship Modeler has a couple of tutorials... scroll down about 2/3 of the way through this page.  The second tutorial shows how to calculate the size of the resistor needed.  If the equations scare you, there are also several LED calculators available online; here's one, but I've never used it and can't vouch for it's accuracy.

Best of luck.

Check model railroad section at LHS for firebox flicker circuits that simulate glow in steam engines -  flicker circuits also popular for simulating flames in dioramas.  Type 'campfire flicker LED' into search engine -everything from DIY to ready-to-install.  Cheapest I've seen was at Dollartree for a battery powered candle-simulator using flickering LEDs - $1.  If only steady glow, look for give-away LED flashlight keychains.