12V wiring question

[Lynden-Jeff]

Hi,

Quick question for you electrical gurus. Wiring up dual 55w halogen reverse lights. Can I put the switch on the negative (black) wire instead of the hots (2 in this case, red/white) and run them directly to the battery? I find it a pain to hook up the switches to the heavier gage wire as im running 10g for both lights.

Thanks

 

[Crumm]

For lights of that size you should really use a heavy duty relay rather than running the main lead(positive or negative)through the switch.

 

[Lynden-Jeff]

I have never used a relay, what is the difference? But for smaller items such as my LEG becons, is it alright to use the negative on the switch side?

Thanks

 

[bbressler]

Smaller items, yes. As long as the current is broken, it will work. You still want to put a fuse as close to the battery on the hot side as you can...if you have a short or something like that, you can do a lot of damage, and the longer the hot side is, the greater the chance.

A relay can be thought of as a trigger. You've got your big wires hard wired into the relay, and a wire running to your switch. When the power is applied from the switch, it opens the relay, and current flows out the big wire. All your switch does is tell the relay to open or close.

 

[Crumm]

Explanation as per quick google search - A relay is typically used to control a component that draws high amperage. The relay allows full power to the component without needing a switch that can carry the amps. The switch only controls the relay. The relay then provides a direct connection to the battery.

 

[95_stroker]

For lights of that size you should really use a heavy duty relay rather than running the main lead(positive or negative)through the switch.

+1

Use a relay or you risk smoke, sparks and or fire....

 

[Lynden-Jeff]

+1

Use a relay or you risk smoke, sparks and or fire....

Thanks for the info. Will look in to getting a relay, what would cause the fire though exactly? Also are there different sized relays etc?

Thanks
Jeff

 

[95_stroker]

Without the relay you run all the amperage through the switch and it gets hotter than hades, the relay takes that load off the switch.

 

[JLDickmon]

Without the relay you run all the amperage through the switch and it gets hotter than hades, the relay takes that load off the switch.

well, what is being asked IS essentially true.. one school of thought in automotive electrical engineering is to switch the ground side, to prolong the life of the switch. Well, this is true to a point, as long as you run less than say 10 or 15 amps through it.. because as a switch wears, the resistance value goes up, and eventually it gets to a point it also becomes a voltage drop, and then you've really got problems..

But anyway, the risk you run switching the ground side is the possibility of a short to ground and melty-melted wires.

So possibly the best thing to do, is switch the relay from the ground side...

 

[dpantazis]

did you look at the wiki pages on intelligent backup lights write up