How We Wire Old Style Sealed Beam Plow Lights
First and foremost I want to point out that this is how we wire the older style sealed beam plow lights, on pre-2007 vehicles. Most 2007 and newer vehicles need to have isolation modules installed because the BCM (Body Control Module) monitors amp draw for all circuits. In other words, the computer knows you added lights, and it does not like it. I also want to point out this is a vehicle specific requirement and has nothing to do with the brand of plow light. The wiring diagram below will work with any sealed beam headlight, fog light/driving light, or any replaceable bulb halogen light for that matter. Since we do mostly Meyer plows, we most often wire "Meyer by Truck-Lite" this way, as well as Truck-Lite ATL lights. I will add more detail to this page as time allows as I get many phone calls about this. I will answer the "Why do it this way?" question now though. Because this way, we do not cut into the vehicle headlight harness. What prompted me to make this page is we just spent about 5 hours repairing a 2000 Dodge 1500 that had the plow lights wired according to the Meyer/Truck-Lite instructions. Rather than tear out the wiring and start over, we tried to save the customer money by repairing what was bad only. BIG mistake. The splices under the battery turned to dust from the acid over the years. There were additional splices under the radiator support (because 1994-2002 Dodge and 1999-2002 GM are POSITIVE GROUND Headlight Systems) that also turned to dust. Thanks to a little help from my friend Jerre Heyer, we also found a blown headlight fuse. The light with the blown fuse was still lit dimly, backfeeding through a bad ground. Lesson learned. So we ended up doing it like we normally do, here is how we do it.
1. Gets connected to the red wire coming from the relay, which must be split to feed both plow lights.
2. Gets connected to the green wire coming off the relay, which must be split to feed both plow lights.
3. Gets spliced into the Marker Light on each side of the vehicle, or you can splice into one and split it to feed both plow lights.
4. Gets spliced into the vehicle turn signal on each side of the vehicle. NO QUICK SPLICE CONNECTORS!
5. Gets grounded with a ring terminal to the inner fender or radiator support on each side of the vehicle. They could also be run to the battery if you like.
Wire colors vary, above are just some standard wire colors. Often the ground is white, so again, verify YOUR wire colors. We use a standard "Bosch Ice Cube" relay for the high beam feed, and the low beam feed. We use a 3 position toggle switch with "center off" to control the plow lights. Up turns on the plow light high beam, down turns on the plow light low beam, and center is off. We connect the power feed for it to "key on" power so the plow lights will go off when you turn the key off. Sometimes when there is a lack of spare key on circuits, we connect it to battery power instead (BUT you have to remember to turn the lights off when you shut the vehicle off). Once wired this way, when you turn on the plow lights, just turn off the truck headlights leaving the parking lights on only. You could plow with both sets of lights on, but the vehicle lights will likely glare off the back of the plow which is annoying. Also, it will be an additional drain on the electrical system that you don't need. Keeping the plow lights completely separate from the vehicle headlight wiring means it does not matter if you are installing these lights on a 1994-2002 Dodge or a 1999-2002 GM that uses Positive Ground headlights. With Positive Ground if you cut the vehicle harness in the wrong place you will suffer unnecessary aggravation, especially if you did not know you are dealing with Positive Ground lights on the vehicle.
In this situation, terminal 87a is not used. When mounting
relays, be sure connections are coming in on the bottom to help shed water.
Adding an inline fuse or circuit breaker (based on wire gauge used) on the power wire from the battery
is not a bad idea. Most of these relays are rated at 40 amps. We use 16 ga. GXL wire for all of this wiring. We use a 20 amp fuse on the battery power wire going to the relay. Since the load is so small on the power wire from the switch to the relay, we do not use a fuse there. Using the 3 position switch, it is not possible for both relays to be on at the same time, so a single power wire from the battery, jumped to the second relay is fine.
Here is the original Truck-Lite ATL Diagram with some of our notes on it, in case you want to wire them the way they were designed to work (though we strongly suggest not to).
On the Meyer web site:
Original Instructions for Truck-Lite with 6 wire switch
Original Instructions for Truck-Lite with 12 wire switch
Original Instructions for Signal Stat Plow Lights
Original Instructions for Dietz Plow Lights
Supplement for Dietz Plow Lights
Meyer Nite Saber Wiring
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Author: Chuck Smith