Plow Light Problems.

[Alan W.]

My BIL wanted me to wire up his lights on his snow plow to his Dodge truck.
He wanted a switch installed so he could choose between the plow headlights and the truck headlights.
Truck uses a control module for the headlights and for some reason has between 6-8 volts on the high beam circuit in the off position. This is enough to fire my relay and cause the plow high beams to stay on continually. Ive tried a few different relay brands and they unfortunately actuate well below 12 volts.
Any ideas on how to stop this.

 

[WranglerX]

I would get operational power (12 volts) for universal BOSCH style 12 volt relay(s) from headlight circuit itself (tap into harness behind headlight) ..... Depending on what he wants to use for lights may determine on what lead off existing headlights he wants to get his relay(s) operation voltage from.... Does he want hi/low beams or just high beams or just low beams....

If you want to control relays (turn plow lights off while headlights are on) I would control the ground path to the relays by a seperate switch on cab...

As for power through relays to lamps I would tap into 12 volts at battery and add a fuse inline....

This takes the computer or power control module completely out of the circuit...

 

[Alan W.]

I have tapped into the headlight circuit, both the low and high, behind the bulbs to trigger my relays. The relays are on a new fused wire for 12 +.
Problem is the voltage that constantly exist on the trucks high beam wire. It fires the relay.

 

[WranglerX]

I have tapped into the headlight circuit, both the low and high, behind the bulbs to trigger my relays. The relays are on a new fused wire for 12 +.
Problem is the voltage that constantly exist on the trucks high beam wire. It fires the relay.

Odd that there is a constantan voltage on high beam circuit.... PCM must be switching "ground" off and on to control lights.... Simple change in how relay is wires could change situation.... You can possibly control relay using headlight "ground" if that is case and apply 12 volts constantly to relay winding....

 

[Alan W.]

Odd that there is a constantan voltage on high beam circuit.... PCM must be switching "ground" off and on to control lights.... Simple change in how relay is wires could change situation.... You can possibly control relay using headlight "ground" if that is case and apply 12 volts constantly to relay winding....

Need to check the ground again but am pretty positive it is constant.

 

[Engineer42]

If he just wants the plow lights and no headlights set the headlight switch to parking lights.

 

[WranglerX]

Need to check the ground again but am pretty positive it is constant.

Might be that head lights constantly powered may be "day time running lights".....

 

[Alan W.]

If he just wants the plow lights and no headlights set the headlight switch to parking lights.

He wants it all run through the factory switch and control. I placed a switch in the cab to break the grounds so he can choose between plow or truck headlights. Parking and turn signals not altered.

 

[loggin]

If the truck has daytime running lights then you may be want to install a switch that interrupts the signal from the high beam to the relay and turn it off only when the daytime running lights are on. When you turn the headlights on, turn the switch to the on position and the system should work with the high beams as intended.

 

[Alan W.]

Might be that head lights constantly powered may be "day time running lights".....

That has crossed my mind but its the highbeams that have the voltage not the low. And both high and low bulbs are single filament halogen.
Nothing illuminates in the truck headlights with the low voltage on.
Looking like I may be putting a separate high beam switch in.