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I want to hook up some more back up lights on my truck but also want to use a toggle switch to turn them on/off and will need a diode to stop the feed back when using the switch. The diode would need to be good for about 30 amps on 12volts. Where can I find a diode likr that?

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    \$\begingroup\$ I don't understand why you need diodes at all. One side of the lights are grounded, the other side is fed from 12 V thru the switch. What feedback? \$\endgroup\$ – Olin Lathrop Apr 2 '12 at 20:14
  • \$\begingroup\$ @OlinLathrop - I think he wants the lights to get powered by the existing feed OR via this new switch. What he's thinking of is basically a diode OR circuit. \$\endgroup\$ – JustJeff Apr 3 '12 at 1:10
  • \$\begingroup\$ @Just: We shouldn't have to guess. This question should be closed until the OP can ask it properly. \$\endgroup\$ – Olin Lathrop Apr 3 '12 at 11:53
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You could do it with diodes, but high current in a diode like that will generate a lot of heat. I don't have time to get into the details right now, but what you'd probably be better off doing is putting a relay near the light, and using the existing high-current signal to drive just the relay coil through a much lower current diode, and then run your new switch signal through a similar diode into the relay coil. This way your diodes only need to be rated for a few hundred mils at most.

A lot depends on the layout of the wiring, and whether there are some lights that ordinarily come on along with the backup lights, that you don't want activated by the switch, but you might be able to do it by using nothing more than a SPDT switch.

If there's just the one set of lights you need to control, and you can locate the wire that goes to them under the dash, here's the alternative: cut that wire and affix the end that goes to the lights to the common lead on the SPDT switch, and the other end (coming from the switch in the shifter) to one of the two throws. Connect a feed from the accessory to the other throw. In one position, the lights will react to the transmission being put in reverse, as usual, while in the other position, they will just be ON as long as the accessory switch is on. Obviously, the switch needs to be rated for the 30A, but a 30A switch is both easier to find and less wasteful of energy than a 30A diode.

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