I don't have the factory marker lights to look at anymore so I can't verify the size. If it is a smaller bulb than an 1156 then (9) 5050 LEDs is probably going to be about your limit to allow for heat dissipation, although I think that will be overkill.
Incandescent bulb numbers tell you a couple of things; base style, base size, bulb size and bulb wattage. For example a 194 and 168 look exactly the same but are different brightnesses due to different wattages.
LED bulbs don't have a standard number system like incandescent bulbs yet. Sellers try to compare them to incandescent bulbs by using one of their numbers to show where they will fit but it really doesn't tell you much about the bulb itself. It just tells you what the base is.
Basically when looking for LED bulbs you need to know the size and style of the base. So using our example, a 194 or 168 bulb uses a Wedge base. You then need to know the voltage. Then you need to look at the housing and judge the amount of room you have and decide how much light you need from that fixture. You need to see where the LEDs need to face to actually work with the fixture since LEDs are directional. This is where it gets complicated..
Bulb designers have no limits so there isn't a set of standards you can go by. Basically you're just guessing. Higher powered LEDs require less of LEDs, but create more heat. Lower powered LEDs create less heat, but require more LEDs. Then you got to measure to make sure they aren't too long or too wide. There are manufactures that have so many LEDs on there bulbs that they won't even fit through the hole for the base...crazy right? This leads me to quality...
Good luck with quality. They all come from the same place. Some will last years and some won't work right out of the box. Keep your fingers crossed on warranty.
I know some have done this conversion and it has worked for them. It's all just guessing though since there isn't a standardized system in place, or a quality standard.
I'd suggest to go with an LED assembly that was designed as such...keyword: design. Most LED bulb upgrade bulbs have no design other then making more and more LEDs fit through a little hole.
I've got a couple hundred dollars of various shape and size LED upgrade bulbs in my tool box right now from before I got my 5 ton. I've been through more than a couple hundred dollars worth over the last couple of years on DOA units, to big for the fixture units, units that run too hot for the fixture, units that last a few weeks, etc. I bought some fog light LED bulbs at $32 from a reputable seller that lasted about an hour. They looked good in the picture and in my hand but when disassembled I found the heat sink for the diodes was in no way attached. They soldered it to the base and not the circuit board or diodes. I say reputable because he did warranty them...with the same bulbs, with the same problem, lol.
I'll add that the website listed in post #7 has good customer service. I've dealt with them several times before. Their LEDs come from the same place though, and are subject to the same issues.
I offer my experience because I've been down this road with very mixed results. A designed assembly is almost always going to be better than an upgrade bulb in every aspect, except maybe price. Good luck in the hunt.
