Short circuit probably not the problem. The pass key system is not being disabled making the car inoperable, thats why it will not crank. Either you are using a key that does not have the correct resistance(black chip in key) or if it is the same key you always used then the pass key sensor went bad. I believe it is in the steering column and a qualified mechanic could help you there.
Safety first before you start, remove all jewelery and your belt buckle or tape using black electrical tape, I have to have my glasses tape the frames if they are metal. Leave the hood open and the battery terminals loose enough so they can be removed qickly if necessary. A CO2 fire extinguiser for fires is nice. The short circuit that is causing the light to stay on is draining the battery to where it doesn't have enough power to start the car. Either disconnect the battery or keep it charged so the car will start when you need to use it. This is temporary until you can find the short circuit. Try to find the short circuit by removing each fuse one at a time from the fuse box (don't put them back in) until the light goes out. Once the light goes out mark down that fuse. Remove all of the fuses and then start re-installing them one at a time (do not install the fuse that made the light go out). You want to make sure only one fuse effects this light, so install all fuses except the one that made the light go out. This process of isolation takes some time and you have to use your logic to figure it out. In my experience I usually find the light switches to go bad, ignition and switches too, you may want to replace them if you can pick one or both up inexpensive at a junk yard or parts store. Has anything electrical been installed in the car recently? Maybe the problem is related to that? The Roadmaster has many circuits like a Cadillac, try to get a copy of the wiring diagram from the public library. This diagram may assist you in finding the problem. Try to visibly inspect for damage as much of the visible wiring harnesses under the dash, doors, power windows, power locks, power seats, power trunk, stereo gear, heating and air conditioning, power seats, trunk, tail lights, head lights, horn, electric fuel pumps, computer and hood as possible. Look for burn marks and use your nose to smell for burns too. Lets continue with logic, if you found a fuse that worked the light, only install that fuse, leave the rest out. Then turn on the head light switch to see if you can get this light to go out or flicker. Try the ignition switch the same way, turn each of these switches off if they don't seem to be the problem. Hopefully, you can find the problem yourself and fix it. I keep a complete log book of every test I do. If you can't figure out the problem, that book could save you thousands of dollars in time testing these things by a technician. It could help a technician to find your problem quickly. Maybe you can leave that fuse out to still use the car. Good luck with your project.
Answers & Comments
Short circuit probably not the problem. The pass key system is not being disabled making the car inoperable, thats why it will not crank. Either you are using a key that does not have the correct resistance(black chip in key) or if it is the same key you always used then the pass key sensor went bad. I believe it is in the steering column and a qualified mechanic could help you there.
Safety first before you start, remove all jewelery and your belt buckle or tape using black electrical tape, I have to have my glasses tape the frames if they are metal. Leave the hood open and the battery terminals loose enough so they can be removed qickly if necessary. A CO2 fire extinguiser for fires is nice. The short circuit that is causing the light to stay on is draining the battery to where it doesn't have enough power to start the car. Either disconnect the battery or keep it charged so the car will start when you need to use it. This is temporary until you can find the short circuit. Try to find the short circuit by removing each fuse one at a time from the fuse box (don't put them back in) until the light goes out. Once the light goes out mark down that fuse. Remove all of the fuses and then start re-installing them one at a time (do not install the fuse that made the light go out). You want to make sure only one fuse effects this light, so install all fuses except the one that made the light go out. This process of isolation takes some time and you have to use your logic to figure it out. In my experience I usually find the light switches to go bad, ignition and switches too, you may want to replace them if you can pick one or both up inexpensive at a junk yard or parts store. Has anything electrical been installed in the car recently? Maybe the problem is related to that? The Roadmaster has many circuits like a Cadillac, try to get a copy of the wiring diagram from the public library. This diagram may assist you in finding the problem. Try to visibly inspect for damage as much of the visible wiring harnesses under the dash, doors, power windows, power locks, power seats, power trunk, stereo gear, heating and air conditioning, power seats, trunk, tail lights, head lights, horn, electric fuel pumps, computer and hood as possible. Look for burn marks and use your nose to smell for burns too. Lets continue with logic, if you found a fuse that worked the light, only install that fuse, leave the rest out. Then turn on the head light switch to see if you can get this light to go out or flicker. Try the ignition switch the same way, turn each of these switches off if they don't seem to be the problem. Hopefully, you can find the problem yourself and fix it. I keep a complete log book of every test I do. If you can't figure out the problem, that book could save you thousands of dollars in time testing these things by a technician. It could help a technician to find your problem quickly. Maybe you can leave that fuse out to still use the car. Good luck with your project.