Dull low beam H4 headlights

NicksTrix

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I have a truck that has some euro hella H4’s in it. mild 55/60W bulbs in them. They are wired through a 30A relay. One for each circuit, total of two. The relays are powered by a common 10G wire and share a common ground. The issue I’m having is:

The low beams are kind of dull, a bit yellowish at night. High beams are nice and crisp the way they should be.

Voltage is only .1 off at the lamp bulb plug from what it is at on the relay on both circuits.

Both left & right are the same. Each light plug has it’s own ground and everything is fresh, high quality components, hwr..



Any ideas? I’ve experienced this before on other builds and haven’t found the reason or solution.

Any insight would be appreciated.
 

Wahl_7s

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Check grounds, I know it sounds simple but its happened to me
 

RelativeEng

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What causes high or low beams is the position of the tungsten filament with respect to the reflector. If you are swapping in aftermarket bulbs, make sure that the filaments are correctly orientated. Just because the bulb fits in the hole, doesn't mean it will work correctly. The bulb could be going 100% but reflecting incorrectly in the housing. If not that, pull out the bulb and inspect the filaments. If you see large amounts of tungsten deposits then replace the bulb.
 

Co-Dog

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I'm not sure that I understand how you have them wired. Is there a switch that operates the relay, and another that switches from high to low beam? If so, you need to check the high/low switch connections and contact resistance.
 

NicksTrix

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the relays carry the load, the headlight switch only is used to activate the relay. the dimmer switch chooses which relay to send the signal to.

i think i've got it figured out. i've got the truck back in my bodyshop right now for a touch up. when it's out i'm going to varify if i've got it solved. i'll post it up if so.

thanks for all the input
 

_

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It's possible the common is on the incorrect terminal causing both filaments to be illuminated in the low setting. The resistance across two filaments (in series) could be so great as to cause the light to appear dim. Insure you have the lamp's common terminal wired correctly.
 

NicksTrix

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ok solved my problem. the headlight plug came wired backwards, so i was back feeding the lowbeam on the bulb itself.
i swapped the ground and low and viola. good as gold.
yesterday i took another bulb assembly i had and varified it with my power supply on the bench. i was able to duplicate the dull lowbeam and was able to get a nice bright one. i noted where the terminals where and checked the truck to find them reversed.

this is the second thing i've found reversed from the manuf of the baseline loom i've used.
thanks for the input everyone. i do appreciate it
N
 
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