Light Bar with 2 switches?

Hi, I have a small light bar that I want to be powered by either a feed from the headlamp main beam, OR from a switched constant live. I have been advised against using diodes as they can burn out, and was advised that it was easy to do with 2 relays, one acting as an intermediary between headlamp and powering a second relay which is triggered by the switch. Will this pose a problem with current going to the switch if say the switch is closed AND the headlamps are on? Could someone draw me something up that will work? I have plenty of 5 pin relays, and think I have my head around it. Thanks.

If you are only powering the coil of a relay there is no chance of you shorting a diode. It will take 2 diodes and 1 relay. Relay as follows   ground terminal 85. Apply Fused constant power to terminal 30. Connect new lamp power wire to terminal 87. Connect wire from headlight through a diode to 86. Connect the banded end of both diodes to 86. One non banded end will go to your headlamp wire. The other non banded end goes to the switch. Connect constant fused power to the other leg of the switch. Diodes to use    1n400x x = any number between and including 1 - 7

That all makes sense, great job thanks.

Ok, now I've got the relay in and working, all good. Diodes fitted and working. Only bit I can't get to work is the headlamp trigger. I think my headlamps are ground switched, as the light bar comes on with sidelights, then goes off with dipped beam, then works fine with flash, only problem is I don't want the bar to come on with the side lights only! Car is a mitsubishi L200. Help!

Or just modify the first one for negative trigger. Ground your switch instead of power. Apply power to the other side of the coil instead of ground. And turn the diodes around.