I purchased a LP kit from Cummins. It came with a low fuel pressure switch, banjo bolt and wiring. I want to put an led in the truck to let me know when the pressure drops. Anybody done this?

 

Dont bother with the LED - you need a full time guage to accurately monitor the fuel pressure.

Alternately, you could install the LED in addition to the fp guage

 

I haven't done it but you should be able to rig one up just like a low oil pressure warning light. Just get the right pressure switch and and remember if you use an LED that they require the correct polarity.

 

Not to mention, polarity but also you need to have the correct resistor for the LED to match it to the voltage required. All bare LED lights will require resistance to regulate the amperage or else they pop. When you buy the LED light, ask them to supply the correct resistor for the max 14V circuit.

 

The long leg on a new LED is usually the one that goes to the positive side, or hot. If they are both the same length, look through the lense and one without the flag on it (the small side) is the hot. Connect the other (short leg or the one with the 'flag' on it) to ground. Put an approximate 700 ohm (or nearest standard value) resistor in line with either leg to minimize current and make your LED last a lifetime instead of 5 minutes. If it is too bright at night for you, just put more resistance in line with it. If it is too dim, take some away. You usually want to clamp your current to 20 or 30 milliamps. Just play with the resistance until you get the brightness you want.

 

another way to tell the positive side is the flat edge of the cover/case of the led.
most packaged leds will tell you what they need in current. better ones even have a diagram of how to figure this out. but they do vary too. bright, ultra bright, color, clear ,etc. i normally run a 471 resistor for my ub blue or ub whites.

 

Ya. What he said. I got some samples in several months ago of the super brights and man, those suckers will blind you if you mount them in the dash.