Need a board design

Just so you know I am very good with wiring and fixing problems on boards but I'm not so good at designing without a reference.

With that said I need a particular board. And any help would be greatly appreciated.

What I need it to do is sense a power connection with a light connection then turn on another with a different power source.
Here is a diagram

(THE PERIODS ARE FOR SPACING)
.......<Light>-----<Splice>---------- Positive Cable / On a bus fuse
..............................|
......................<Power sensor>----- Positive Cable / On a different bus fuse to power a second light
............................./
............<Light>----

The reason is that I am trying to wire in a brighter backup light for my truck because my windows are tinted and I can't see it at night.
So I don't want to overload the Amperage on the fuse for the reverse light.
Some may say to just up the fuse but I don't want to do that.
Because I also want to add this to my boat trailer.

That was an original idea that I had.

Here it is drawn out (AGAIN PERIODS ARE FOR SPACING)

.......................+12v 2nd light VCC source
...........................|
.......................LOAD AKA Second light
..........................|
........................../
1st light VCC...-|......NPN 2N3904
.........................\
.........................\/
..........................|
........................Ground

But I was wondering if this might be too simple and short out.
That's why I was wondering if there might be another way.
Maybe a more protected circuit?

The thing that I was going to use it for is a Xenon light set.
It takes up to 55W
12V and (10amps max probably for startup) runs between 7-9amps
I just don't want to reach my limit on just the reverse light.

Basically, all you need is a 12V relay, a diode, a fuse, and some wire. You need to make sure that the fuse, wire and relay are rated to carry the current required by the added lights.

kchriste said:

Basically, all you need is a 12V relay, a diode, a fuse, and some wire. You need to make sure that the fuse, wire and relay are rated to carry the current required by the added lights.

Click to expand...

Thanks for the help you think this will do?
AutoZone.com | 40 Amps 12 Volts replacement relay | 40 Amps 12 Volts replacement relay

I want to have both lights on.
A relay might be easier but I I just want a single coming from the primary light, not two.
With a transistor it would do it that way I want.
Please I need help.

Superman-- said:

I want to have both lights on.

Click to expand...

The relay will let you do that and the one you posted the link to above will work fine.

A relay might be easier but I I just want a single coming from the primary light, not two.

Click to expand...

I don't know what that sentence means ----^^^^

kchriste said:

The relay will let you do that and the one you posted the link to above will work fine.

A relay might be easier but I I just want a single coming from the primary light, not two.
I don't know what that sentence means ----^^^^

Click to expand...

A relay might be easier but I I just want a single LINE coming from the primary light, not two.

Well I'm just going to use a relay it appears to be the quickest way to get it done.

Thanks though

Superman-- said:

A relay might be easier but I I just want a single LINE coming from the primary light, not two.

Click to expand...

With a relay you only need one connection from the "primary light" to the coil. The other side of the coil can go to chassis ground. I thought this was clear in the diagram I posted:
**broken link removed**

Yes you did I was just a little tired when I wrote that and was thinking that you wanted it to go back to the light.
It looks great and when I get my lighting I'll put it in thank you very much.

can v get the details means circuit diagram for microcontroller based access controll system