Diodes for LED's and other lights?

[mongoose]

On a previous post it was mentioned that Diodes were needed to keep power from back feeding into other LED's as one switch was turned off. My question is this. If i am wiring accessory back up lights up on my truck and want them to work two ways. one is with the original wire trigger and the other is with a switch so they can be used a work lights. Do i need diodes or anything to help protect the wiring or the lights? Also being a vol firefighter, would it be possible to wire up my fog lights with a wig wag and still be able to use them as they would normally function when not using the wig wag?

 

[Gray Ghost]

Anything is possible with enough money. Yes you will need diodes. Think of them as a one way valve. If you put two sources of current to a light, when one is activated, current will flow up the other path. With a diode in the line, it says no way jose. Just make sure the diode will handle the current, or it will burn up. plan your wiring on paper and figure out which way the diode should be installed. Then go wire it up.

 

[mongoose]

thanks gray ghost! will have to do some planning!



what specs do i need to look for in order to get the correct diode? i've never messed with them. do they list voltage ranges or such or how are they rated? where would be a good place to pic some up?

 

[AggieJustin]

Backup lights

Mongoose-



I've got some auxilary lights wired up on my rear bumper similar to what you described. They activate when I put it in reverse and also with a dash mounted switch. I didn't use a diode, but I did use a relay to feed a new wire back to the lights to keep them off the backup light circuit. It works great, plenty of light in the back now.



I have a diagram I can send you on how I wired them up if you want.

 

[David_VT]

It is usually a good idea to use the right diodes to protect circuits and to make it easier to troubleshoot after the fact.



If you use the same power source (circuit) as the shifter uses, and your 'manual' switch simply goes around the "Ram's" switch then you may get away without a diode. This would be sort of like putting two switches on a house light, one for each door. (not exactly but close). However doing this does not in itself offer you any extra current capacity to drive extra backup lights.





One way to attack this is use the B+ power lead that feed the trailer plug as the power source for your extra backup lights. (via an additional user supplied appropriate sized in-line fuse as the B+ feed will pump a ton of juice before blowing a fuse whilst shorting out)



Power the command side of a relay with a tap to your reverse light circuit at the rear of the truck. Attach the B+ tap (above) to one side of the relay and your aux light feed to the other side. When the reverse lights go on, the relay is commanded 'on' and the juice will flow from the b+ tap to your new lights.



Once the above is done, if you make a cab switch to manually jump around the transmission switch, you have the ability to turn all the reverse lights on at your whim. (I added a very bright LED to warm me not to leave the switch on while driving down the road)



There are countless ways to do this and most are just fine, especially if you err on the side of protecting your investment with a little extra planning and protection. (fuses, diodes, etc)



Enjoy (but don't burn up your truck!)

 

[stg2500]

I have been wanting to modify my lights like this since I put them on. Currently they are just switched using a relay. they can only be turned on when the parking lights are turned on.



Can anybody give me descriptions or diagrams for wiring the lights to operate with the truck back-up lights as well as with the switch from inside the cab?



Thanks for the help.

 

[Evan A. Beck]

Here's how I have mine done... Switched with reverse, and with a manual override in the cab. I have a wiring diagram I can send... Email me if interested! -- email address removed --

 

[Spaceace]

white nights

This is exactly how the White Nights(Geno's Garage) are wired. Relay and switches are located in the housing though. I tapped the constant 12vdc and back up 12vdc on the trailer circuit to run them.

 

[mongoose]

thanks for the help guys. now it is time to add the backup lights and do the turn signal conversion!

 

[CJ Johansson]

Diodes - ratings, etc.

Originally posted by mongoose

thanks gray ghost! will have to do some planning!



what specs do i need to look for in order to get the correct diode? i've never messed with them. do they list voltage ranges or such or how are they rated? where would be a good place to pic some up?

You can get diodes from any electronic sales place. Radio Shack even has 'em. A couple of other places to try are www.newark.com and www.digikey.com these two have a *MUCH* better selection than R. S.



As for ratings, diodes are rated by their reverse breakdown voltage and current handling capability. The reverse voltage is how many volts it takes to make 'em non-one way (and it generally kills 'em in the process). The kind of diodes we're talking about are often called rectifier diodes. Most rectifier diodes are in the 100V or more range (well, you can find just about anything, for 12V automotive systems, anything over 30 volts is fine). The current rating is just that, it will handle what it's rated for, and just about no more before it goes "poof". Fortunately, they are easy to find in the 10 to 100 amp range.



To figure out what you need, take the wattage of the lamp and divide by 12 (volts). A 55 watt lamp will use 4. 58 amps. A 5 amp diode would work, but I'd double it just to be safe (incandescent lamps have a big surge current until the filament heats up). So, a 10 amp 30 V diode would work for lamps up to 55 watts (headlamps), and probably would cost about 50 cents.



-cj

 

[David_VT]

Looks interesting, check it out

http://www.wireconnections.com/

 

[redneckdr]

aux backup laghts

i just rewired mine yesterday. there is a backup light connection in the trailer wiring harness. i put a relay in place, fed from the 12v+ in the trailer connection, triggered from the backup wire from the trailer harness. i installed a pair of 55w halogen lights from auto zone. i haven't wired a switch yet, but may at some time. so far, if i want the lights on for work lights, i'll set the park brake, switch the "ignition" on, and put the gear selecter in reverse. the original backup lights are now amber turn signals.

 

[Thomas]

Herb,



Since you have a 4X4, you can also turn on the backup lamps while stopped with the engine running by putting the transmission in reverse and the transfer case in neutral.

 

[redneckdr]

work lights

good idea , thomas. i hadn't thought of that. no need to run the extra wire, now.

 

[mongoose]

Thanks for the help on the diodes, now i' know what i'm looking for!!! you guys are great!

 

[David_VT]

Don't forget Dave Fritz's site when wiring

There is a ton of stuff on his site, look around it for modifications, etc:



http://dodgeram.org/tech/mods/index.html#wiring

 

[stg2500]

Thanks for the wiring diagrams. I will post once i get a chance to do the conversion to the new wiring.

 

[RJ2]

CJ---- In changing over the backup light lens to an amber led bulb, can a and/or gate be put into the left and right tail light circuit so if it sees the brake light(which activates both at once) it will not make. So the brake lights would be normal but the new amber leds would only light if one at a time? You would not need to mess with the trailer wiring.

 

[CJ Johansson]

Originally posted by RJ2

CJ---- In changing over the backup light lens to an amber led bulb, can a and/or gate be put into the left and right tail light circuit so if it sees the brake light(which activates both at once) it will not make. So the brake lights would be normal but the new amber leds would only light if one at a time? You would not need to mess with the trailer wiring.

Well, yes, you could use logic gates to determine what to do with the lights. Unfortunately, most logic gates are designed to operate on 5V or less (there were some CMOS gets that would run up to 9V). They would fry on the 12V system we have. Of course, you can level convert the signals to 5V, run all the logic on a 5V regulator, then use drivers to get back up to 12V, but it gets to be a real pain.



You could probably do it with a couple of diodes and a couple of transistors, but then you'd have to figure out what to do about the case when you are sitting stopped with the brakes on, but also the turn signal on (waiting to turn).



-cj

 

[redneckdr]

rear lights

i just redid mine. i picked up the turn signal from the trailer harness, and ran to the "backup light" socket, after installing REAL backuplights. i then disconnected the stop/turn wire from the red taillights, and ran a wire from the white/tan wire in the loom to the original stop/turn wire on the socket (through a relay). the white/tan wire is a connection for an aftermarket high center stoplight, as in on a topper, etc. the red stoplights are on steady, with the brakes. the ambers come on also with the brakes, but then one or the other will flash with turn signal, while the opposite amber stays on solid with the red light on that side. i think that can be stopped by disconnecting the white/tan wire at the "multifunction switch" (turnsignal switch). then, to have brake/turn signals on a trailer, with standard hookup, you would have to add one of the modules availabe for vehicles with separate turn signals and brake lights, which convert the 3 wires from the truck, back to 2 wires to operate the brake lights and turn signals on the trailer.

i just chose to let the ambers operate like the current red turn/stop lights. another brake light on isn't necessarily a BAD thing.