Not too long ago, I bought a cordless drill from Goodwill and morphed it with half a set of jumper cables in order to have a mobile drill at camp (see it here!). That project turned out really well and left me with the remaining half set of jumper cables, which aren't good for much by themselves.
Luckily, I soon stumbled across another cordless treasure that had been tossed to the wolves. This was a Cyclops flood light and I happened to be right there when it was rolled out of the back and hefted onto a bottom shelf. I pounced on it immediately but found that it was the kind you have to plug in and charge. No adapter was included. I'd be willing to bet the behemoth was given the old heave-ho either because the adapter got lost or the battery stopped holding a charge. I would bet on the former, because this still has all the new stickers, including one that runs across the power button. I popped open the waterproof battery compartment and found that it runs off a 12 volt battery! This could be what my sad, half set of jumper cables has been waiting for.
My Goodwill find was $20, which is WAY more than I usually spend on anything there. Before shelling out that kind of dough, I looked the model up on my phone. It's a Cyclops C15MIL Thor Platinum halogen model, rated at 15 million candlepower. New, they run about $70. So the Goodwill price was better, obviously, but didn't include a warranty or adapter. Given that it's 12 volt, however, I was willing to gamble 20 bucks.
Step 1: Get a Flood Lamp
Step 2: Inspect Power Supply
You need 12 volts
Step 3: Remove Battery and Strip Wires
I cut the battery free and stripped about an inch off the red (positive, I hope) and black (negative) wires. The battery can't be thrown in the regular trash. I'll have to figure out what to do with that.
Step 4: Jumper Cables
Next, you'll need a pair (or half a pair) of jumper cables. I see these at junk stores all the time for around $5. I had half a set left over from an earlier (drill) project. I stripped the ends of the red (positive, I know) and black (negative) cables.
Step 5: Inspect Battery Compartment Hatch
I found a foam block glued to the inside of the battery compartment lid. This popped off easily and was discarded.
Step 6: Ingress
We need some way for the jumper cables to enter the battery compartment. I found a drill bit that was the same diameter as the cables. I drilled two adjacent holes in the compartment hatch. I then snipped out the piece of plastic between them and smoothed things a bit with a knife blade.
Step 7: Feed Jumper Cable Ends Through New Hole in Battery Compartment Lid
Step 8: Making Connections
Using wire nuts, I connected the red lamp wire to the red jumper cable. I then connected the black lamp wire to the black jumper cable. I then wrapped each connection in electrical tape before wrapping it all together and tucking it into the battery compartment.
I don't plan to swing this thing around by the cables, but it's not unforeseeable that the cables might get tugged at some point. To keep the connections from being jerked up against the compartment lid, I cinched a zip-tie around both cables, a couple inches beyond the electrical tape.
Step 9: Plug N Play ... Or, More Accurately, Clamp N Play
Wrapping up, I re-installed the battery compartment hatch and slowly drew the cables out until the zip-tie stopped any further progress. Then I sealed the hole with silicone, making the unit waterproof again.
Now the floodlight sits comfortably in the SUV until needed. At camp or roadside, I can pop the hood, clamp the jumper cables to the battery, and have an awful lot of light at my disposal.