[MoparNorm]

Back up lights come on every time you are in reverse, independent of the headlights.
You don't need power from the battery, the wire to the back up light(s), is the hot wire. You only need to add a ground.
However that will not give you the feature you need and it would be fairly complicated to wire the lights to work only when in reverse and only when the headlights are on.
It may be simpler and less costly to wire a switch from the battery, then direct to the lights and operate them manually as needed.
If you go that route, you should use a lighted switch so that you can tell when the lights are on and off from the cab during the day.

 

[valiant67]

I would think you could accomplish what you want by using a relay that requires two inputs to provide an output of power to your backup lights. One input would obviously be the signal from the current backup light system. The second signal would be from the license plate illumination circuit or rear tail light - that would be a good source at the rear of the truck for an indication the headlights were active. Once the relay sensed the presence of both inputs, the power (where ever you source the +12v from) would then be transferred to the auxiliary lights you install.

 

[av8r115]

using a relay that requires two inputs

Great idea! I didn't know such a relay existed, but it makes sense now that you mention it.

You don't need power from the battery, the wire to the back up light(s), is the hot wire. You only need to add a ground.

I'm installing a set of halogen driving lights purchased for another vehicle but never installed. Can the existing wiring handle the extra current?

 

[AllanC]

I'm installing a set of halogen driving lights purchased for another vehicle but never installed. Can the existing wiring handle the extra current?

I think the wiring would be able to handle the extra amperage draw. The more important concern that I would have is the dash mounted headlamp switch. It very well might not handle the extra current draw without tripping. You might have to add relays to each front headlamp circuit. The dash headlamp switch when activated would close a relay for the left front and right front headlamps. With the headlamp relays closed, battery power would be directed to each individual headlamp.

Adding headlamp relays is quite common on older collector cars from the 1950 - 1960 - 1970s when incorporating halogen headlamps on those older electrical systems. You want to use 2 relays instead of 1 for reliability. If one fails at least you would have 1 headlamp available for night time illumination.

 

[av8r115]

I did some reading up on relays and how they work, and apparently a single relay that uses two circuits to control a single circuit is unusual. What I think I'll do is use two SPST relays in series; the first one controlled by the license plate lights that when closed will ground the second relay which is controlled by the backup light circuit, and closes the circuit for the auxiliary backup lights. Haven't decided on the power source yet.

 

[MoparNorm]

Great idea! I didn't know such a relay existed, but it makes sense now that you mention it.


I'm installing a set of halogen driving lights purchased for another vehicle but never installed. Can the existing wiring handle the extra current?

Your best source of information will be from the manufacturer of those lights. If they have a website and if the lights are still fairly recent, or in production, they should have the amperage draw specifications and may even list them on their website.
That circuit may be 10 or 15 amps, the halogens could be as much as 30, so you need to find out first, to protect your existing wiring.

 

[awyseguy]

My opinion on the best, while requiring a little more effort and expense.. It will do as you wish.. is to use the 2 relays.. 1st relay gets power when the lights are on(taillight or license plate light); and the second switched off of the back up lights.. with a main power feed to the front of the car, I would suggest a 12ga wire from the battery to the relay, then relay out to feed on #2.. and over to your lights.. 12 ga is still easy enough to work with, plenty for a pair of driving lights, will handle the power over the distance, and will be a more HD wire for securing along the way.. Then everything uses a good body ground at the tail end of the car. Sounds easy enough.. I just added an entire secondary relay panel to one of my Dakotas.. using a Dakota Fuse/ Relay panel..I added that to support my electric fan.. and later stereo.

 

[bmwjohn9]

I don't know how bright you need the reversing light to be. I have a 50w halogen in one side, and a 35w halogen with beeper in the other. Some improvement and NO wiring needed, just swap bulbs. I have considered adding the LED front parking lights as seen on e-bay (Audi style?) and tapping directly into the back up light wire. The LED lights I know add very low current draw, but may not add a great deal of light. This would not work if wiring up two Cibie foglights as back up lights, as they are 55w each, and with your regular lights would really need a relay and extra wiring, IMHO. Still, changing bulbs might be a good first attempt. NOTE: Halogen bulbs generate significant heat, so I would NOT leave it in reverse while parked, talking to friends, etc. or you might melt the lens.

 

[JTE]

Realize that adding driving lamps under the bumper they will become the first thing to hit when you go up a steep driveway.

 

[av8r115]

It's finally a clear warm weekend when I don't have to work, so I'm finally installing these lights. How do I tell which wire going to the tag and backup lights is the hot wire? There's not a wiring diagram for the back end in my Haynes. I want to tap into the hot wire so if the associated bulb goes out, I'll still get power to the relays.

 

[AllanC]

The following information is the color coding used on a 1991 Dakota. I would expect it to be the same for a 1987 model.

Backup lamps: VT / BK tracer
tail & tag lamps: BK / YL tracer
turn signal lamps: BK / LG tracer

You indicated that you want to use relays. Where are you going to mount the relays? Be warned that if mounted under the bed in the rear of the truck location is subject to dust, dirt, road debris and moisture which is not conducive to relays working properly after many years.

 

[av8r115]

Thanks Allan. The relays will be in a protected area. They're cheap and non-essential, so if they do fail I can replace them and fashion some sort of box for additional protection.

 

[av8r115]

The lights work as planned on the first test! I'm not sure what I did wrong because all of my projects usually take 2 or 3 tries!

Thanks for the input guys!

 

[lalunette]

The lights work as planned on the first test! I'm not sure what I did wrong because all of my projects usually take 2 or 3 tries!

Good to hear everything worked out.

Ya, I know that weird feeling when you get something right the first time. Happened to me when I started winterizing my '68 2-stroke 20 hp Johnston outboard. It started on the first pull the next spring and I just couldn't believe it. :scared:

 

[av8r115]

Well, my aux backup lights have started blowing fuses. It took a day or two for it to sink in that I didn't insulate the wires where I zip-tied them to metal parts. :facepalm: Oh well, at least the weather has cooled off.

 

[AllanC]

Manufacturers learned years ago that insulating wires with rubber grommets, wire looms, additional sheathing material, etc is necessary for long term durability. We do-it-yourselfers in a hurry to get the job done have to be reminded periodically - At least this kind of fix is simple.