rewiring modding need advice

I'm working on a four wheeler and need to mod a couple things and need your advice on how best to do it

1) tailight is wired to be on all the time and I'm going to rewire it so it's on only when the headlights are on. I've identified hot wires for both low and high beam headlights. Here's the part I need help on though - if I just splice into those wires (basically T the tailight wire into both the low and high beam hot wire) won't I back feed 12v through to the other system? For example if I select low beam headlights won't the high beams still get power because of my splice? Does this need a diode or something wired in when I do my mod? If so can you please advise me on what I should get and how I should wire it up? (radio shack items hopefully)

2) I've got a winch to wire on this thing and forward or reverse on the winch is accomplished just by reversing polarity. How can I wire this up with stuff I have on hand instead of spending $60 for the switch kit from the winch manufacturer? I'm thinking a two way toggle switch, but then current load is a problem for a normal switch so maybe a relay? But then do I need to wire two separate relay circuits? One for forward and reverse on the winch? and then the same question I have in the taillight crops up again - are things isolated properly that way so no power goes the wrong way?

hope that makes sense, thanks for applying your 12v knowledge!  

Diode isolate the high and low beams together and run them to a relay.  Then, use the OEM tail light feed to power the tail lights.  Basically, when either light is on the relay will energize and the tail light will turn on.

I, too, would tap the winch at the battery.  Depending on the real estate you have to work with you can either get a big DPDT switch like above or go with a lower current (on)-off-(on) switch that drives relays.  You can set the relays up in a standard "5 wire" configuration so that both sides of the winch are always grounded.  Then, if you energize one relay or the other the ground is taken away and replaced with 12vdc.

Just what I needed on the taillights, thanks - any particular radio shack diode I should ask for?

A smaller switch and relays is what I initially thought of since smaller switches are easier and cheaper and I ahve 30amp relays laying around from old fog light kits.

But someone told me that the winch runs a 50 amp circuit breaker.

Any hints where I could find a 50amp+ DPDT switch?

I'm probably not saving any money by the time I find either a switch rated for 50+ amps or two relays rated for same....I guess I'm stuck blowing the money for the OEM switch set up.

Thanks for the help!