Snowstorms hit at any time of day. Sometimes that means it’s the middle of the night or early morning and completely dark. Being able to see when backing up the truck while pushing snow is crucial. These PlowSite members discuss how to wire on more lights for your plow truck.

DeereFarmer: I’ve done a ton of searches on this topic. It is a very common topic, but I’m a little confused. First, my ’02 GMC has the factory plow prep package and towing package with the 7-round plug. I also have the factory AUX light switch. What I want to do is mount two reverse lights under the bumper for added rear lighting. My windows are tinted from the previous owner, so it’s hard to see to begin with. What is the proper way to add these lights? I don’t really want to wire a switch so they are on when I want. I just need them on when the truck is in reverse. Can I just wire them directly into the stock reverse wires with a relay? Do I wire them into the trailer backup lights on the 7 way? I don’t have any trailers with backup lights. Is there an easy way to add them into the AUX switch? That’d be pretty cool. What would you guys do?

BigLou80: I have the same truck and use my AUX switch for my strobes. Just pull off the side panel behind the driver’s seat and you will find the relay. Sorry I can’t be of too much help on how to wire the backup lights, although I would just find the wire for the trailer and add a relay.

basher: If you use the reverse wire from the trailer towing package, you shouldn’t need a relay unless the lights have a very high amp draw. Look on the driver’s side frame between the cab and bed, there could be an accessory harness there for gooseneck/fifth wheel applications. This is normal for any general 3/4 ton with a tow package. You could splice a longer one onto that with a good crimp fastener. I suggest a low-temp solder-filled heat shrink connector.

Yard5864: I just spliced into the 7-pin trailer connector with two tractor lights under the bumper and it works great with no problems.

Photo: PlowSite member yard5864

basher: The 2002 Chevy will have a U.S. car connector. While it and the plug you show are the same from the trailer side, the U.S. car is a molded two-piece part and has no accessible terminals. But the reverse will go to the center.

ChevKid03: I just put a set on the back of my ’03 2500HD because of the same reason. I have blacked-out windows that are extremely difficult to see out of at night when backing up. I ended up purchasing a set of reverse lights from the local parts store. If you have a test light, you can find the reverse light wire and wire the hot one from the new store-bought lights to this. Then run a ground anywhere on the frame.

B&B: Just a tip here for you guys running hi-amp backup lights. Do not direct-wire lights into the stock reverse light circuit if they draw more than 10 amps max without using a relay. The stock reverse light circuit is not externally relayed in these trucks, and it travels directly through the reverse light switch as well as the body control module – neither of which are designed to handle more than a 10-amp additional load in addition to the stock reverse bulbs on that circuit. Use a relay.

Famouslee99gt: I know you said you didn’t want to hook them up on their own switch, but I did this on my ’99 Z71 and I love it. I like to leave them on when plowing. They are also useful when hooking up trailers or wagons at night, and they’ll stay on when you are in park hooking up the trailer. I personally just like having them on their own switch.

DeereFarmer: B&B, could you give me a quick lesson on relays? What do I need to buy as far as relays go? How do I wire them up? Also, how much harder would it be to run them to a switch? I just don’t want to drill a switch into my dash and run a wire through the firewall all the way back.

B&B: A relay is nothing more than a remotely activated hi-amp toggle switch that can be remotely activated with a low-amp circuit, such as a small toggle switch with a light-gauge wire, or in the case of reverse lights, the factory reverse light switch. Its purpose is to carry the hi-amp load from the power source to the accessory that you want to operate without needing the hi-amp power run through your tripping mechanism (reverse light switch in this case). Relays can be wired dozens of different ways depending on what you’re using them for.

basher: You will be able to find all the wires required to use a relay with in the goose harness. The power supply, the signal and the ground are all there and readily available. Use a diode if you plan to use both a dash switch and shifter to energize them.

mkwl: I did this (no relay) with mine. I guess they draw less than 10A because I’ve had them on there for almost a year with no problems — knock on wood. They are cheap $19 ones, but they work well.

DeereFarmer: OK, so I’ve read a lot on this subject and think I have it down. I’m going with a relay for sure. Let me make sure I have this correct. There are four prongs to a relay. One is a hot lead from the battery, one is a ground (more than likely I’ll run this from the battery as well just to be safe), one is a trigger (in this case probably run from the stock backup light, correct?), and the final one goes to the load (new backup lights). Now, here are a few more questions I have:

  • To power a pair of 55-watt lights do I need two relays or just one?
  • What gauge wire should use?
  • On a standard relay, how can you tell what prong goes to what function? Most relays I’ve seen aren’t marked or anything.

I’m pretty sure I’m ready to tackle this project. I’ve done a lot of trailer wiring and wiring for trailer hitches so I do have some experience on the subject. Just don’t want to screw up my truck. Thanks, guys.

B&B: You’ve got it. A single relay is plenty for two 55-watt lights. Most generic relays will handle 30 amps each. Use 14 gauge for the battery power wire as well as the wires to the lights from the relay. The ground and trigger wires can be much smaller since they carry little current, 18 gauge is more than enough. Make sure to fuse the toggle switch power wire (5 amp is plenty) as well as the power wire to the battery (15 amp will do it). If you look on the underside, most generic relays are marked with the corresponding pin locations.

Cet: I know you said you didn’t want to use a switch, but when I put my lights on my truck I used an on-off-on switch through a relay. I can have them on all the time, every time I put the truck in reverse or not on at all. I didn’t want them on when I didn’t need them, and I also wasn’t sure how much power they were going to use. If my truck started to get low on power, then I wouldn’t use them at all. That’s never happened though.

DeereFarmer: What if I want to go way overboard and wire up four lights? I have two 35W tractor lights for under the bumper and also two 55W CAT lights that I was thinking of maybe mounting on the top of the bumper right under the stock light housings. It might be overkill, but I’m just thinking. Want to get it all planned out before I start tomorrow. Is there a relay out there that can handle 60 amps?

B&B: Just add a second relay if you want and use your toggle (or whatever tripping method your using) to trip them both. Most Bosch-style generic relays like we’re discussing here are 30 amp, some are 40. There are relays that will handle hundreds of amps, but they’re under the solenoid classification like a snow plow under hood solenoid (which is just a large relay) and would be way overkill for your intended application. A single 30-amp relay will actually support over 300 watts, but they tend to melt the wire terminals when running too many wires off each pin on the relay.

Bruce’sEx: I’ve got mine on a switch at the moment, but I’m upgrading to the on-off-on system. I like the idea, and it is more flexible for what I need and when.

Read more on PlowSite: How To Properly Wire Additional Reverse Lights?

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