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Old 06-27-2010, 11:01 AM
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scottmcphee scottmcphee is offline
1987 w124 300D
Join Date: Mar 2008
Location: Edmonton, Canada
Posts: 1,539
stock 9004 bulbs are 45/65W lo/hi

I just bought some 80/100 bulbs and I am upgrading the wiring in the car with new hi temp bulb sockets and relays, running fat wires from headlight directly back to the battery. All fused of course.

I'm doing in such a way that uses headlight pig tails that will keep stock headlight sockets, wiring, switches, etc.. intact. I just mate to the stock bulb socket inside the headlight housing.

Many people say just running direct battery power to the headlights (through relays) like this is enough to boost even stock bulb brightness, bypassing all the thin wires and routing through switch and current sense module, etc, which all drop voltage. Bulbs' rated wattage is based on 11.7 volts to accommodate all the voltage drops through wiring, so 45w at 11.7v turns into 53w at 14v (if that's what your meter shows at the battery when charging by alternator). There's an equation about luminance to wattage, etc. and when all the math settles, it's a significant increase in light output when you boost wattage by 20%, the payback is more than 20% brighter.

But what the heck I'll see what 80W per side can do as low beams. If it's blinding, or whatever, I can put stock bulbs in and still be better off for it.

The only downside might be the bulb out warning indicator may come on the dash. But both sides being balanced (relays for both hi and low beams on each side) may just fool the current sense, if it's just doing a compare instead of an absolute current check on the headlights it should be OK. We'll see. Ha ha ! I made a funny. Anyway, if the dash indicator drives me crazy I'll pop out the current sense module, if that works, or the dash indicator bulb.

If I had Euro lights, I wouldn't be doing any of this. But this is a lot cheaper and I can do it today, so I will.
Scott McPhee

1987 300D

Last edited by scottmcphee; 06-27-2010 at 11:14 AM.
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