I want to take some blue cold cathodes and convert them so that I can use them in my car. I was reading up and that through a cig lighter there is a 12 volt DC.

(1) Is it possible?
(2) Where could I get a cig lighter adapter to convert/solder?

thanks for any help in advance/.

Quote: Originally Posted by teh_spazz I want to take some blue cold cathodes and convert them so that I can use them in my car. I was reading up and that through a cig lighter there is a 12 volt DC. (1) Is it possible? (2) Where could I get a cig lighter adapter to convert/solder? thanks for any help in advance/.

It's deja vu all over again ....

Wiring accessories up to the ciggy lighter supply is pretty ghetto ... I'd suggest you get some big phat cable (4 ga or bigger) & ring terminals & connect straight to the battery, get a flash looking fuse holder & a big fuse (like 30A) for it (but don’t fit in until you’ve completed the wiring) + attach to the +ve cable, & run those cables through the bulkhead into the passenger footwell - you might be lucky & find an existing grommet, but you'll probably have to drill & file a new hole - make sure it's clear on both sides & use a grommet.

Run the +ve phat cable to a distribution/fuse box - you can never have enough live feeds once you get into car modding - make sure you put it somewhere passengers can't accidentally stomp on it, & run the phat earth/ground/-ve cable to a junction box so you can ground all the accessories directly to the battery (rather than through the bodywork).

An average CC draws 3 watts - assuming you're going for four, that's 12W - or 1 Amp - so whack in a low rated fuse in the distro box, & you've got the live feed you need for the tubes. The draw of a couple of invertors isn't a big ask for most switches & cable, so you could just run the feed to a switch in the dash. Unless your car is ultra high-spec, there's probably a switch blank you can use - either get a switch meant for the car (stealthing is always good), or dremel the blank out so you can get a standard switch in there. Split the output from the switch & run to the +ve line of your invertors … run the ground sides back to the earth junction box.

If all is ok, once you fit your main fuse & flick the switch all the lights should come on … if it’s not ok, you’ll blow a fuse rather than set fire to the car.


If you want the CCs to come on when you open a door, wiring is a little more complicated – you’ll need a 4-pole relay. Find the wire running to the pin switch on the drivers door, cut it inside the car, extend the cut ends & connect the 2 cut ends to the relay – one on the 85 terminal, and one on the 86 terminal. At that point, your courtesy lights should still come on – accompanied by a click from the relay.

Run a live feed from your new distro box to the 30 terminal on the relay, and run a wire from the 87 terminal to the +ve line on your invertors … the –ve side should be connected to the –ve/earth/ground junction box as above.

One extra refinement – you can put a switch in the wire running from the 87 terminal on the relay to your invertors – that way you can make sure you don’t get a blinding blue light when a cop asks you to get out of the car

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Jonny: I have no doubt that your way is The Right Way, but what's the harm in wiring the lights to the underside of the cigarette lighter socket? (I'm not trying to be a punk; I'm genuinely asking since it sounds like you know what you're talking about). As you mentioned, the average cathode draws about 3 watts, and the cigarette lighter supplies something like 150W, with fuses already built in (wattage varies by vehicle, of course). Especially if you never use the cigarette lighter, seems like you've got a good power source just sitting there...

Quote: Originally Posted by FunkyFresh Jonny: I have no doubt that your way is The Right Way, but what's the harm in wiring the lights to the underside of the cigarette lighter socket? (I'm not trying to be a punk; I'm genuinely asking since it sounds like you know what you're talking about). As you mentioned, the average cathode draws about 3 watts, and the cigarette lighter supplies something like 150W, with fuses already built in (wattage varies by vehicle, of course). Especially if you never use the cigarette lighter, seems like you've got a good power source just sitting there...

The problem is that cars are bulit down to a price, not built up to a standard. Specifically, the wiring tends to be the minimum that'll do for the intended load, with only a small safety margin.

If you assume that the average lighter socket needs 3 metres of wire & will draw 150W (12.5A), then using 32/0.20 cable (capable of handling 16.5A) is ok, but using 28/0.30 cable (which will handle 25A) would be better, but it costs 7p a metre more. Saving 21p on wiring the socket, multiplied by a production run of 250,000 gives a saving of £52,500, multiply that by all the wiring in your average car, and there's a huge economic benefit to using cable with a 40% safety margin rather than a 100% margin.

This isn't a problem in normal use, but as soon as you start adding accesories the risk increases ... in this case, not enough to be a big risk, so if all you ever want to add is 2 cathodes, and assuming you use proper connectors & add an extra fuse, then there shouldn't be a problem.

My reason for posting the "right way" rather than the simple way is that once you've tapped into a convenient supply, the temptation to add more accesories to that source is very strong, and it's easy to get to the point of overload/overheating ... & you also end up getting a rats nest of extra wiring.

+, what happens when you sell the car? If you leave any bodged wiring in there, and the next owner wants to add something else, they may well tap into your extra wiring ... & possibly use a paperclip rather than a fuse when their new toy burns it out ... & they'd probably have no hesitation in suing you when the car goes up in smoke.

That's the worse case scenario, but to sum up, if I'm posting advice, I want to what I can to make sure that advice doesn't lead to:
1 - unasthetic mods
2 - fires
3 - litigation

Perfect, thanks! Nobody every looks back on a mod and says, "Man, I put too much time into doing that right!"

(Unaesthetic mods and fires and litigation, oh my!)

EDIT: Been reading up on fuses & best practices; BCAE has a good writeup on the basics.

Hmm I think I might have to do this on my car... Match up red cathods to my displays and have then under the dashboard... hmm cool idea thanks!