Built this little device
The problem: My LED gauge lights keep burning out. They're cheap eBay 194/74 lamps, so the regulation on the lamp is clearly inadequate. The dimmer rheostat on my car is burnt out. I have 2 good ones, but someone's done something with the wiring, and I know from experience that as soon as you do that, chances are the first thing that happens is you burn out that rheostat. Instantly.
What I really SHOULD do is figure out what was changed, and undo it. This is the plan with the help of my shiny new 1990 TEWD. In the meantime, I just want my dash lights not to burn out in a matter of a couple of weeks.
Given that the lights actually work, and don't burn out instantly, I figured that what they need is just a little extra safety margin. The rheostat was bypassed using a length of wire with a pair of male spade terminals plugged into pins 3 and 4 of the wiring harness connector. Given that I've installed LEDs, I'm not going to dim the lights anymore... Well, not really, and I'm certainly not going to get a linear response from a rheostat anyway. (I might build a PWM controller in the future. I think it'd be kind of a cool project, but I'd have to isolate the dash lights from the other things on that lighting circuit, and I'm not going there now.)
So... A simple idea. A resistor to induce a voltage drop. I tried a single 10 ohm/5W resistor at first, but the climate control doesn't really like it, and will decide to shut off. It visibly dims the dashboard lighting as well. Not terribly so, but noticeably. I actually kind of like that at night, but I don't like the climate control deciding that it's TOO dimmed, and shutting off. I COULD have gone back to the store and bought a smaller value resistor, but instead, I decided to make use of Ohm's law, and just paired the devices. Half the resistance with 2 in parallel. I also get twice the power dissipation, so it should be good. With a little luck, this is enough buffer to the LED lamps so that they won't burn out right away.
I bought enough of those LED 194s to do the marker lights and sth, but with the performance in the dash, I'm just not going to. I guess I'll use them for other 12V PC based projects, where the 12V provided isn't going to climb to ~14V ever, and be nice and regulated. They will probably last a good long time that way.