Hello everyone, long time reader first time poster. I have recently purchased a 1999 Ram 1500 Sport with the quad headlights. When I turn on my high beams, all lights work properly. When I turn off the high beams, the low beam on the driver side stays on as it should, but the low beam on the passenger side turns off with the high beam. I've checked all fuses and relays and they seem to be in working order. I have 9004 bulbs in the high beams and 9007s in the lows. Any ideas on why my passenger side low beam won't stay on without the high beam also being on?

 

Grab the service manual for your truck from here. Wiring diagrams are in section 8W. As I recall, left and right low beams draw power from two different circuits........

 

It seems to me that the wiring is correct although those diagrams can be a bit tricky to read sometimes. Could it be the multifunction switch? It seems odd that only one side is acting up and if it were the switch it would be both sides.

 

Ok, left headlamp is powered directly from the switch, right headlamp is powered from the security relay in the PDC. (under the hood.) Although, according to theory, the both should be tied together at Joint connector 1, in the PDC....... Swap the bulbs from side to side, see if the one that don't work follows the bulb.

 

A few comments from the peanut gallery....

As a rule the bulb should never use both filaments at the same time (exception being a headlight flash) because of the heat generated. So the low beams staying on does not sound right.

In the 2000/2001 FSM the wiring diagram shows different bulb pinouts in the outer headlight depending on regular or quad setup. That's the A and B labels with the dots. From what I gathered that is so all headlight bulbs are the same to avoid confusion. The 98/99 FSM doesn't show the quad wiring so it might be different but I doubt it.

The 9007 and 9004 have different pinouts *and* the notches in the base are different. If the bulbs sit differently in the housing then one of them is wrong.

More info: https://sparksmith.com/blogs/news/do...and-9007-bulbs

 

I switched the low beam bulbs around and the problem followed the bulb. Bought a new bulb and the problem was fixed. I assumed that since the bulb turned on with the high beams it wasn't bad but I was mistaken. I found the manufacture date printed on the bad bulb: Nov. 19, 1998. Kudos to Sylvania for making a headlight bulb that lasted 22 years. Upon further review, the other three bulbs have similar dates so I imagine I'll be replacing my share of headlight bulbs in the future. Thanks to HeyYou and DerTruck for the suggestions!

 

Just replace them all now. They have led a good life, and they do get dimmer as they age.