12V and halogen don't need a relay. The switches will be OK if not broken or worn out.
You would be wasting time, wiring, money and possibly adding voltage drop.
But do what you wish.
Optional wiring:
Fuse box power to light switch, light switch to dimmer, dimmer to bulbs. Direct wiring from dimmer to H4 headlight plug, no connectors, no terminal boards.
Standard sealed beam 12V headlights are 65W high beam each= 130W = 10.8A total. Same as the H4 halogen and same as the original 1937 bulb. No new electrical stress will be introduced.
P.S. Larry...I see "horn" in your title but no mention in post. I think that means you decided on that from your other horn post?
