I am looking to wire a small LED light bulb to illuminate my Pac Brake toggle switch. I am looking to wire it to a constant positive, so it will be ALWAYS ON.

I read that the LED light draws almost nothing and lasts 10,000+ hours. Is this true? If so, there shouldn't be any problems then with having it always on...

 

I don't see why it would be a problem those things last a long time and like you said the draw almost no power.

 

You could run an LED for weeks on a motorcycle battery, let alone 2 huge truck batteries. No worries installing that LED, or 20 if you like.

 

If it is just an LED do not forget to install a resistor in series with it to limit the current, most run between 2.0 to 5.0 volts unless it is specified for 12 volts then the resistor will integrated into the package.
LED's will last of thousands of hours unless you abuse them or drive them at their limits then they will die quickly.

 

great place to get some is plasmaled.com

 

Is it OK to run a power wire (fused) directly from the positive terminal on the battery for the LED?

The resistor is already installed in-line with the LED.

 

I don't see why you couldn't, as long as it is fused. I'd think there would be some place more handy to tap under the dash, though.

I agree about their power use. I've got a little LED thing that attaches to my bicycle handlebar to light the computer at night. It runs off a watch battery, which I've never needed to replace...

 

You could run it to the battery, but be sure the fuse is at or close by the battery because if there ever was a short then all of the wire run from the battery to the fuse is unprotected.
You could use a 1 amp fuse to protect the line at the battery.
Even though LED's do not draw much current they still can become hot enough to burn in some instances as with High Output and Luxeon, but not your case.