wiring backup lights the right way? - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 4 (permalink) Old 03-21-2006, 05:06 PM Thread Starter
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wiring backup lights the right way?

Ok, I bet I sound stupid, but I tried wiring my backup lights through the trailer backup lights, and obviously its too much power for the circut because it blows the fuse every time. Where should I be hooking into for it to work when I put the truck into reverse? Thanks, I'm sure its a dumb question.
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post #2 of 4 (permalink) Old 03-21-2006, 05:16 PM
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To do it right you need to use a relay.. At least thats what I did and it works great. You can tap the trailer, but I tapped the driver side reverse light in the tailight. All it does is flip the relay, and walla, high powered backup lights...
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post #3 of 4 (permalink) Old 03-21-2006, 07:33 PM Thread Starter
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Oh i see, alot easier than i thought. You can get relays at any auto parts store right?
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post #4 of 4 (permalink) Old 03-21-2006, 07:49 PM
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you mean like this

Smart Auxiliary Back up lights. Model A

Background: I purchased a nice set of docking lights at my local marine retailer, they have stainless and composite housings, plus a bright 65 watt halogen bulb. This makes them perfect for the rear of my truck hanging off the receiver hitch.
You could purchase lights from many places.
The problem with most installations is you either have to turn the lights on manually or wire them to trigger with your factory backup lights. Both are just not professional in nature, we as enthusiasts have the technology to do it right.
Plus if you wire them to turn on when you shift into reverse, they will turn on even in the daylight. Boy talk about, in my opinion a waste. And if you wire them to a stand alone switch, they are no longer automatic, and that’s the whole idea here, to make them a fire and forget item.
So I developed a way to turn them on in reverse, but only if the parking lights are on. I.E. if it’s dark enough to need parking or headlights, you probably need bright back ups.
It’s a very easy item to build and is very reliable, I am also working on a Model A1 that will cancel the lights if you have a trailer harness plugged in to the truck trailer harness.

Items needed:
Environmental wire splices for 14, 16, 18 and 22 gauge wiring (These are splices that are soldered to the wire ends then sealed with heat shrink rubbing to make a very long lasting connection. You could use scotch-loks and regular crimp splices if you’re so inclined. Be sure to tape them up and seal the ends with some good clear rtv to prevent corrosion and continuity problems later on down the road.

Two continuous duty relays capable of handling 25-30 amps. Radio shack has them by the bag almost and at good prices. They last a good while and are pretty reliable. You could spend 20-30 dollars on a real nice NAPA one but it would be overkill.

$6.29 Brand: RadioShack
Catalog #: 275-226 Model: 275-226
• Coil Rating: 12VDC, 160mA, 400Ω
• Contacts and Ratings: SPST 30A at 12VDC
• Size: 2x1-3/16x1-1/8"
I am by no means pushing one brand over another. These are just inexpensive.

Optional consumables: project box from radio shack they make em big and small but the 3” x 5” will work. To put the relays into and seal up after the work is all done.

6 feet of wire in at least four colors, all but one could be 16 or 18 gauge, but one for the load will need to be 14 gauge.
Male and female butt connectors to plug into the relays, clear RTV, nylon zip ties (prefer black), roll of GOOD electrical tape.

Two stainless steel hose clamps with at least an open circumference of 11 inches, and two fat 1” x 1” rubber bushings, similar to shock absorber mount bushings. This will allow attachment of the lights to the receiver without drilling into it.

Millimeter, wire strippers, wire crimpers if you use crimp connectors. Phillips screwdriver, straight slot screwdriver, needlenose pliers, side cutters (dykes) and a bright flashlight.

Explanation of my madness: This way if you read this and understand it, you can avoid reading the dry parts about finding the correct wire, etc.

My setup is basically a simple logic module using a feed source (parking light feed), an input from the backup light circuit and a 12v key on powered input.
And provides for a power source that can handle the loads with over powering factory switches and harnesses.

It requires three “yes” inputs to power up the lights.

First relay is wired as follows
Input to the switch side is from the parking light feed.
The 12v source that is switched on is provided from the factory reverse light feed (This can be found at the back of the seven pin trailer plug, or at the junction of the factory wire harness just above the rear bumper on the driver side frame rail. most trucks).

The ground is well… hooked to a ground on the frame. Plenty of factory grounds to tie into.
The output is 12v that was supplied by the reverse light input .This is the first “yes” to the module. If the reverse lights are triggered then we have power waiting to be switched on. The next yes is if the parking lights are on. If they are then the relay will switch on the 12v supplied by the reverse lights.

Next we move to relay number 2.
The Input to the switch side, is supplied from the output of relay ONE. 16/18 gauge wire
The 12v source is supplied from the trailer 12v battery charge feed, it is a “key on” feed (Third YES). Use the 14 gauge wire for this
The ground, again ground it.
The output will be the power to light the auxiliary lights. 14 gauge wire

So now we have the basics.
Parking lights on? YES
Shifted into reverse, factory backup lights on? YES
Truck Running or “ON”? YES
Then we will get illumination on the auxiliary lights.

All inputs can be gained from the trailer harness to the seven pin plug. If your truck has no trailer plug. Look under the truck near the driver’s side rear frame rails. All the plugs are there.
So now we have the power to illuminate the auxiliary lights.
Mounting them has several options. You can attach them to the bumper, or attach them to the receiver hitch. I attached mine to the receiver hitch main support that spans the width of the frame. You can’t drill or weld here. So I used the long hose clamps. To attach the aux. lights bracket to the receiver. And used the 1” rubber to isolate the metal bracket from the receiver. This allows for a shock mount and an easy way to re-align them if you back over something.

Now that we tested everything and it works. Take the relays and tie strap them together. Then take the clear RTV and completely encase them in the clear stuff. Placing them in a sandwich bag works well for providing a holding cell. Place the relays into the bag all wires hooked up. Close it around the tip of the RTV and squeeze away to fully cover everything. Let it dry or place it wet into the project box, it will remain watertight for quite sometime.
Then securely attach it up out of harms way.

All done, removing the spare helps tremendously in gaining access to the wiring.
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