I plan to wire up some 12 volt LEDs as indicators for some accessoriy switches. I know I need to wire them in parallel with the circuit, but someone told me I need a resistor to limit the current flow through the LED... is this true? If so, how do I know how much resistance I need? It's a 12 volt LED going into a 12-14 volt system, so do I still need it?


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98 Explorer (Lemon Law Case in Progress)

'00 F-150, X-cab, 4x4, Lariat, Off-road, Trailer Tow, Holandia Sunroof, built 11/99 picked up 10/00!
List of planned mods: Clear corners and tails, CB wiring, Stainless brush guard, at least 1 set of KCs (probably more!), custom radar detector mount, color matched trailer hitch with stainless steel ball, torsion bar tweak, bug deflector, spray in liner, and a tonneau of some sort...

 

Radio Shack has a bunch of LED's with different current ratings. If you have trouble just use Ohm's Law, V(volts)=I(current)*R(resistance). The volts are basically fixed at approx. 13.2 by the battery so choose a resistor that will allow a current that the LED is rated for.

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'00 5.4L 4X4 Lariat (Black/Silver)
'99 Ranger 4.0L 4X4 XLT

 

Cool, but that means that I would need a 1.32 kilo-ohm resistor to reduce the current to 10 mA, right? What happens if I mis-calculate it, and too much current flows? Does it melt, or just burn out like a bulb would? If it's too bright, I can always add additional resistance so it's not blinding at night, right? If I use the resistor, won't that also drop the input voltage? Does the input voltage even matter? I've taken more circuits and electronics classes then I care to remember, but we've never focused on LEDs, just diodes in general... That's why all the dumb questions... I just don't know how they work. Maybe I should just ask one of the doctorates in Electrical Engineering out at school tomorrow..... :-) I'll let you know what I find out and post some pix when I get it all wired up.
-Joe-


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98 Explorer (Lemon Law Case in Progress)

'00 F-150, X-cab, 4x4, Lariat, Off-road, Trailer Tow, Holandia Sunroof, built 11/99 picked up 10/00!
List of planned mods: Clear corners and tails, CB wiring, Stainless brush guard, at least 1 set of KCs (probably more!), custom radar detector mount, color matched trailer hitch with stainless steel ball, torsion bar tweak, bug deflector, spray in liner, and a tonneau of some sort...

 

Radio shack sells LED with the resistor already attached in red green and yellow.
Also in 2 or 3 different sizes and brightness




Just run the red lead to the output side of the switch and the black lead to a ground. There is a bar that the stearing colum attaches to that the best ground under the dash.

Hope this helps

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GOLD RUSH

'99 F150 XLT SC SB 4x2 Harvest Gold
Factory[*]5.4[*]3.55 limited slip[*]Trailer towing package[*]In-dash CD player
Aftermarket[*]Ford Beanie bear[*]Slip on extender mirrors[*]Powerstop brake controller[*]Covermaster C1000 topper with wing[*]BugflectorII[*]Ventvisors (front&rear)[*]3 www.f150online.com decals[*]Ford Lumi Logo[*]Steelhorse Billet grill[*]Ford hitch cover[*]Yellow wire loom[*]Hyper White head light bulb[*]Fender badge on tailgate[*]Painted to match AVS slotted taillight covers[*]Ford system 4 alarm[*]Clear turn signals[*]"Blazer" strip reflectors under tailgate[*]FORD script antenna painted to match[*]Cup Holder courtesy lights[*]IonOptics driving lights as reverse lights[*]12 Volt power outlet in bed[*]Power port/Cigarette lighter courtesy light[*]4 Driving lights in grill[*]Next who knows???

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[This message has been edited by Firezap (edited 11-07-2000).]

 

You're right about the 1.3 k-ohm resistor. If you miscalculate i.e. too little resistance you will simply fry the LED. Yes you can add more resistance to dim the LED. Why not put a variable resistor in for now to see how bright you like it at night? Then measure the resistance and use that value as a guide. Of course make sure that the variable resistor has the correct range. The input voltage does matter, V=I*R but it's not a problem. But remember, a LED is still a diode and only allows current to flow one way.

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'00 5.4L 4X4 Lariat (Black/Silver)
'99 Ranger 4.0L 4X4 XLT

 

Great pictures Firezap. I'm posting this typical circuit partly because I've never posted a picture before.



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'00 5.4L 4X4 Lariat (Black/Silver)
'99 Ranger 4.0L 4X4 XLT



[This message has been edited by gah (edited 11-07-2000).]

 

Firezap, what do all of those switches control?

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'00 5.4L 4X4 Lariat (Black/Silver)
'99 Ranger 4.0L 4X4 XLT



[This message has been edited by gah (edited 11-07-2000).]

 

That wiring diagram is essentially 1/2 of what I plan to do. The problem is that I can will have a DPDT center off switch, so I can power the accessories from more than one source. (all 6 will have switched power, 3/6 will have steady power and 3/6 will have flash-to-pass power) To wire the LED in-line would require at least 130 mA current capacity to support the relay. Plus, it doubles the number of LEDs I need... I wish to indicate not only whether or not it's on, but by which power source, hence the 2-color LED. (Incidentally, it's here.... http://www.radioshack.com/product.as...Fid=900%2D1467
Or here for a slightly recessed look... http://www.radioshack.com/product.as...Fid=900%2D1465 )

The problem I have is that I can't wire up this relay in line because it only uses 10mA for the red and 15 mA for the green. It says that they are 12 volt LEDs... does that mean that the input voltage needs to be 12 volts? (When I put the resistor in to step the current down, it'll step the voltage down to almost nil...) And I have to wire the LED in parallel.... I plan to use the DPDT switch, with 2 inputs. (Example, one switched lead and one steady lead) Then, use the center terminal as the output to the relay. Next, connect the output of the first side as an input to the center of the second side, and then I have my two outputs to the LED that are based on the switch position. The switch can handle 3 amps, so I should be ok on that front, but I really don't want to have to drill 12 holes for LEDs. There's got to be a way for me to use those dual color leds... I'm going to go talk to one of the instructors tomorrow... I had him for my Intro to EE course, and he's got a doctorate in Electrical Engineering, so I think he'll be able to get this figured out. Thanks for the help, guys. I'll let you know.
-Joe-

By the way... got the clear corners in tonight... took all of 10 minutes! Half of that was getting the pass side headlight out... didn't need to, but the parking lights were tight in there. [sigh]... my first mod.... [welling up...] :`-)

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98 Explorer (Lemon Law Case in Progress)

'00 F-150, X-cab, 4x4, Lariat, Off-road, Trailer Tow, Holandia Sunroof, built 11/99 picked up 10/00!
List of planned mods: Clear corners and tails, CB wiring, Stainless brush guard, at least 1 set of KCs (probably more!), custom radar detector mount, color matched trailer hitch with stainless steel ball, torsion bar tweak, bug deflector, spray in liner, and a tonneau of some sort...

 

I just got the info back from tandy... it's a 3 volt input.... just to complicate things.... *****!

 

GIJoeCam, that's an elaborate set up. Let us know what you find out.

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'00 5.4L 4X4 Lariat (Black/Silver)
'99 Ranger 4.0L 4X4 XLT

 

The top 2 are for my lights in the grill. The middle 2 are for the lights in the lower part of the bumper (when I get them) and the bottom 1 is for my reverse lights. It's a 3 way one side is from the tail lights and the other is from the starter relay power.

[This message has been edited by Firezap (edited 11-08-2000).]

 

My factory cupholder lights didn't work that well so I added the LED's and they work great. I also added 1 to the power port area so we can see in there.

 

I bet one in the door handle area would be nice. The handle would hide the led but the light would still backlight the handle.

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2000 F150 XLT 4x4 Short Bed. Amazon Green, 5.4L, SuperCab, ORP, Tow Package, Sliding Rear Window, Electronic Shift, Keyless Entry, LT265-70-17 Tires, Clarion Pro Audio, Herculiner Bedliner, Air Silencer Removed.

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So Firezap, I'm guessing that the LED's are only on when your side lights and/or head lights are on right? I didn't even know that my cupholders had a light.

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'00 5.4L 4X4 Lariat (Black/Silver)
'99 Ranger 4.0L 4X4 XLT

 

That's cool. What about the LED's in the cup holders?

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'00 5.4L 4X4 Lariat (Black/Silver)
'99 Ranger 4.0L 4X4 XLT