Tail light Relays

ok, here ya go - there's two possibilities for the types of bulbs you're using, assuming you're using two filliment bulbs (1157's) -- your bulb sockets can be either self grounding bulb sockets, or non grounding (isolated) types.  i've included pics for both.  -- here's the non self grounding type:

that one will save you from having to install an extra set of relays - and it prevents the rest of your lights from failing to operate, if you say - had a front bulb burn out.  now, this next one is if your bulb sockets ground to the tail light assemblies - you can actually use this in both situations, but it comes at the cost of another relay per side

i realize that you could use a single relay on each side if you have ground insulated bulb sockets, and let the single relays coil be provided ground by the opposite circuit, but that isn't as reliable - these will operate without being affected by the removal of a bulb on the other side, or in the front (though you may need to get an electronic turn signal flasher that requires little or no load in order to flash, since it will only be loaded down by the current of the front turn signal bulb, and the relay (which is much smaller a draw, but still it will flash most conventional turn signal flashers anyhow - try it first, if it flashes too slow, or not at all, get an electronic one for a few bucks at any auto parts store)

Ack!  i uploaded the same pic twice!  sorry about that...... here's the self grounding type pic....... doh!

but before you go using either of those (though they both will work) -- just save yourself a lot of unnecessary bull, go get yourself some new ground isolated 1157 sockets (plastic sockets with their own ground wire in them, that don't ground by plugging the bulb in) - and use this circuit (i don't know why i used 4 relays before, i must of been asleep at the helm - you only really needed three....