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Old 12-31-2002, 12:44 AM
Joseph_H's Avatar
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Location: Texas
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Installing larger wattage headlight bulbs?

My car uses H4 headlight bulbs rated at 55/60 watts. Could I use the larger wattage bulbs there are 80/100 watts and 90/100 watts without compromising anything?

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Old 12-31-2002, 02:41 AM
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I do not know for sure if you could not step up the wattage, but higher wattage means higher amperage is coming thru. Systems are fused for a given amount of amperage or current.

If you were to step up to a higher wattage and then blow a related fuse, you'd know why.
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC

Last edited by Mike Murrell; 12-31-2002 at 12:55 PM.
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Old 12-31-2002, 05:50 AM
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Location: Newcastle upon Tyne, UK
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Mike is right but there's more to it.

A 60 watt bulb draws 5 amps at 12 volts, a 100 watt bulb draws just over 8 amps. So with two uprated bulbs you're going to draw an extra 6 amps. This may well blow the standard fuse. However, just putting a bigger fuse in to stop it blowing, does not change the fact that the existing switches and wiring are now handling those extra 6 amps. So yes, you may well be compromising things. Sparking at switches and relays, plus wiring running hot are possibilities.

Plus, more heat in the headlamp housings can start to melt plastic fittings!

Just as a final thought, is it legal where you are?
Cheers, Neil
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Old 12-31-2002, 05:52 AM
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Location: Surrey, Uk
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Higher current may damage the bulb failure module.
Mick J
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)
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Old 12-31-2002, 10:14 AM
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You can without too much trouble use relays and heavy wire to handle the extra current.

The real problem will be the damage to your headlights over time due to the additional heat. I got a set of Euros on a parts car. When I took them apart to check them out there was a terrible burned electrical smell. Also the extra heat had corroded the adjustment bolts that are plain steel with no corrosion coating. I discovered a set of 100 Watt bulbs in the glove compoartment. I'm sure that they had been in there and caused these problems.

If you have Euros I recommend NOT using high power bulbs, the damage is not worth it.

Additionally, the most important part of your headlight effectiveness is the reflector shape. The Euros reflect the light where it's needed, so you don't need extra lamp power.

I believe that if you go to 100 watt bulbs, you will eventually regret it. See that you have good standard wattage bulbs that are not old. They do lose a little brightness with age.

Good luck,
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Old 12-31-2002, 12:28 PM
'82 300TD-T
Join Date: Oct 2001
Location: SoCal
Posts: 276

if you do follow the upgrade path, check the following:

daniel stern has some great info under the tech section "Why and how to upgrade your lighting circuit."
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Old 12-31-2002, 04:48 PM
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Join Date: Nov 2002
Location: Texas
Posts: 231
Thanks for your responses

The reason I was asking is that for my car there are always more than one wattage option for the bulbs and I didn't know if I could just up the wattage with no problems, but after reading your responses above, I realize that it is not a good idea. Of course I didn't want to go the route of upgrading fuses/relay and wires... so I’ll stick to the specs.
As for the legality of upgrading the wattage, I really don't know and doesn't matter now.

This is a great forum with many helpful folks like you guys!

You all have a wonderful New Year!
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Old 12-31-2002, 05:13 PM
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I have 80/100 in my car 4 years with no ill effects and all I changed were the bulbs

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