Headlight LED swap Issue -Solved

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dudeman2009

Senior Member
Joined
Feb 9, 2016
Posts
1,562
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Location
Arizona
Ram Year
2001 1500 Sport with enough electrical modifications to make my brain hurt
Engine
Magnum 360
About 3 weeks ago I had ordered some LED headlights. I'm running the sport headlights with the Quad bulbs. Since i'm a little hard on cash I only got my headlights at that time and never used my fog lamps as I thought it would look stupid. When I did use my fogs, they were still halogen so I didnt notice anything wrong. However once I switched to LED fogs I had a problem. My high beams would come on and the high beam indicator would light ever so faintly. After a few days of tracking this down I determined it to be caused by the LED headlights.

The way the non DRL quad bulb setups work is a little convoluted in my opinion, but once you understand it, no more difficult than any other setup. The fog lamp relay gets its power not from the battery, but from the high beam rail.

When the high beam selector switch is in the low beam position the rail is at battery potential as sourced by a few things. The High beam indicator light, the quad lamps relay, and the two high beam filaments in the outboard lamps. The primary source of current should be the high beam filaments, not the quad relay or high beam indicator. Since I don't know what I did with my old 9007 bulbs I can't actually test them. However it calculates out to about .39-.45 ohms. The measurement I got from my LED high beam rail was closer to the Kilo-ohms range. This cause the current for the fog relay, about 150 milliamps, to be drawn through the quad relay and the high beam indicator. this tested to be true when I pulled the quad beam relay and the high beam indicator got brighter.

The solution for those of us who are switching to LEDs is to put a load resistor between Battery positive and the high beam wire. No more than 15W power rating or about 14 ohms. This will fix the problem of your high beams turning on when you turn on the fogs but not burn out any wiring or switches.
 
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