I think you may be thinking of resistor and not transistor. If you put a long enough cord on it, you'll get a voltage drop that way also. I think Jim Thomerson has made mention of this on a few occasions and I have seen him use it. Put about 3 foot of lamp cord on it and try lighting an old glow plug with it while checking the voltage under load and that will tell the tale for you and if I'm remembering correctly, it will make it simpler for you also. Use a battery fresh off charge also.
Type at you later,
Dan McEntee