To start with, the lights on my truck work normally. When I tried to wire in new plow light on my 99 Ram, I spent 2 days chasing my tail. In the end, describing the current state and asking questions is all I can do.


When I pull the headlight bulbs out of the connectors on the Ram and test the connector contacts with a test light, both connectors to the filaments have power all the time. It doesn't matter if the lights are off and the key in my pocket, both connectors on both sides have power all the time. I even pulled the headlight switch out of the dash and removed the headlight relay from the PDC, but both connectors are hot as long as the fuses are in the PDC.


Is it possible that the factory switched the common (ground) side of the headlights? If the lights work normally, then they must be using variable resistance to power the high beams. Or, my truck is broken and I have a different problem.


When I wire in the plow lights using the normal connections, the ground for the plow lights energizes the truck headlights and completes the circuit and the lights on the truck go on even though they are turned off.


I'm stumped. If they did switch the ground circuit, how do you wire another pair of headlights into the circuit? If not, any idea what's wrong with my truck that it has power when it shouldn't?


Thanks in advance for any info

 

Your test light is probably for continuity not voltage. You should use meter. Power gets switched on for the lights and it's not getting power all the time. Tap into the correct wire and you will get your lights working.

 

We have the 9004 bulbs. Your ram switches the positive and all power for the lights goes through the headlight switch, no relays. Use the ground contact in the headlight plug. I had problems too when I used body ground vs tote ground in the plug. Not sure why, when looking at the wiring diagrams, the plug ground IS body ground. Go figure.

How/where did you wire in your plow lights?

 

As shown by moparite, you are looking at the bulb end, remember to mirror it for the headlight plug.

 

yes indeed, the switch provides ground path.

 

First, the bulbs are correct for the truck and there is power to the back of the bulbs on this truck because the headlight switch is switching the ground side of the circuit. Just a quirk of the 99 to 01 trucks.

The lights work just fine on the truck. But, because the circuitry is Volkswagon-esque, I can't figure out how to actuate an external relay for an external set of lights when it is normally actuated by a positive power flow, not a ground. Besides, the grounds are conflicting and causing other problems when the new ground feeds back through the headlight circuit and turns on the truck lights.

Does anyone have any good information about now to wire in external lights to this kind of system.

Please stop guessing if you don't know.

 

No, it's just a test light and it lights up when I probe the two contacts on the harness connector that go to the filaments. I have power all the time on both sides of the truck. And, the truck lights work properly. I just can't figure out how to hook in a set of plow lights.

 

Well, you could always just run a hot (I would do a switched hot) to your relay coil. Then run the other side of the coil to your ground at the bulbs. You could also use the hot (low or high, not both) AND ground from the bulbs. Or did I miss something and this is what you are already doing?

Or worst case, just add a switch, separate relay and keep them on a different circuit altogether. You could still do a switched hot that would kill them when you shut down the truck.

 

You can spend days on the website below. Maybe this will help...

http://www.the12volt.com/relays/relaydiagrams.asp

 

Didn't the plow come with a harness for the plow lights?

The headlight switches in these trucks are notorious for being overloaded, and failing. (and occasionally burning down the truck......) So, I would be real tempted to set it up with a relay that just switches which headlights are controlled by the headlight switch. (not to mention simply changing the system so the normal headlights are powered by a relay that is controlled by the headlight switch......)