JonCat,
I wouldn't do this, but I wouldn't stop you if you did. Buy some of the Xmas lights that are all wired in series. Divide the number of lights by 10 (the ratio of 120 volts:12 Volts) wire the 10 strings all in parallel. Example: 100 light string divided by 10 = 10 lights per string, 10 strings. Increase the fuse rating by 10 also. Use larger wire to the points where the 10 strings are connected in parallel. If you see more than 2 wire comming out of the plug from the original light string, it is a series parallel combination and this scheme as written does not apply. If this doesn't work or your tractor catches on fire call 911, not me. /w3tcompact/icons/wink.gif
Al