As GRJ suggests, the electronics suggests these are NOT LEDs. For one, LEDs have + and - polarity. Yet, even though the manufacturer obviously has red and black wiring, they chose to use 2 red wires to the drum lamp, and 2 black wires to each marker lamp. If you can read the lettering/markings on the circled component, it should tell us the bulb voltage.
Some additional comments if you plan to do an LED conversion. It appears that your marker lights are in a housing with 3 lenses facing front/rear/sideways...and that they may be multiple lens colors such as the amber/red shown above. Your photo suggests the bulb is fed into the marker housing through a single hole.
I can't quite tell but it appears that GRJ showed earlier a 3mm diameter LED for a marker. But if your marker has 3 lenses, you will probably want to modify a 3mm white LED. An off-the-shelf 3mm LED with the rounded-dome lens projects light in a somewhat narrow-conical beam. With a small file, emery board, sandpaper or whatever lop-off the rounded dome to make a more flat-top, as well as creating a "frosty" surface which better scatters light sideways. This will better emulate the wide-angle of an incandescent bulb to illuminate all 3 lenses.
I mentioned earlier but did not illustrate another technique when using the LED strips. You can remove an LED and insert a 2-wire extension cable from the vacated solder-pads to a remote white LED. Here's a surface-mount LED and a 3mm LED using this technique. The surface-mount LED was one removed from the strip itself. Perhaps obvious but note that you can use this extension-cable method for any LED on the strip. You do have to mind the polarity - red/black wires shown for +/- in photo below.
Wiring up these tiny LEDs can be a soldering challenge, but you can buy pre-wired LEDs which can reduce some soldering hassle. The benefit of this technique is you don't have to mess with resistor(s). And if you are using GRJ's lighting board to drive the LED strip, you get the advantage of constant-brightness, no-flicker, and DCS-compatibility.
