Electrically inclined people...
I have a topper on my tacoma that has a dome light that runs of 2 C batteries. The topper is has an LED brake light that is wired to the trucks's brake lights. The dome light is great, but I don't like that it runs off C batteries rather than the truck's 12V. How would a person go about wiring the dome light to the brake light so it runs off the truck battery? The wiring for the topper brake light is right next to the dome light, so if it is possible to tap into that wire it would be really slick. Anyone????

 

I already threw in my two cents, but here's a recap for YotaTech:
The current light runs on 3v DC - scrap it. If you tap into the wiring for the 3rd brake light, then the interior light will only work when your brake lights are on.
Get a new 12v light (pretty cheap). You then have the choice of tapping into an existing power source, which can be hot all the time or only when the key is in the ACC or ON position; or you can get power directly from an auxillary fuse block or the battery. If you run directly to the battery, be sure to use an in-line fuse. With this set up, it would also be a good idea to put the light on a timer or switch that only allows it to operate when the topper's lift gate is up. This way you can't forget about it and drain your battery.

 

when I had a top on my 94 Ranger, I didn't have a dome light at all.
I went to autozone and bought a 12V light, and ran a wire along my frame rail to the battery (fused it of course). I used a wire harness (like your brake light in the topper has) so when I took off the topper, I didn't have to cut any wires.

 

the 12V bulb sounds logical. But how will the wiring itself actually work? Do I splice the 12V+ to one of the + where the batteries go, then the - to the other battery location? Or do you mean toss the whole 3V light assembly and get a 12V one? Actually, that does sound the easiest...

 

Just ditch the 3V and get a whole 12V assembly, it will only run you $5

 

The closest place to tap off is the parking lamps.. This way you can not forget it during the day and the most you need to do is to have the park lamps on at night.. Either that or run a new wire up to the batt. via a relay that is switched on by the key.. I would not run straight to the batt., if you do you are asking to leave it on in the day time. I think for the effort the parking lamps are your best bet.. I would also install a rubber 2 pole pigtail disconnect between the cap and the bed in case you ever need to remove the cap, you can do so with out cutting the wires.

Good luck, and I would personaly buy a thin florescent light instead.. the diffrence in light output is freaking amazing and will not draw too much.. (I would be more willing to install right off the battrey with a florescent)

 

Thanks for the ideas, I like the parking light one.

 

I used a mercury switch to activate the dome light in my old top.

 

Yep, good advice. Since you'll only need the light at night, you could tap into a parking light to provide the +12V for the new 12V dome light, then use a mercury switch mounted to the rear window to provide the ground to the dome light when you open it.

I think there's a mercury switch in the 4Runner tailgate that operates the rear cargo light. I seem to remember the light coming on halfway through the opening of the tailgate. Maybe you could find one at a junkyard, or maybe someone else here has worked on it, and can verify. I didn't see the rear door light switch in my Mitchell CD's interior lighting wiring diagram.

Here's a link for mercury switches ~$7:

http://www.lakemetro.com/mercury_rel...t_switches.htm