stupid question about overwatted bulbs - PeachParts Mercedes-Benz Forum

4NDELIT · #1 11-30-2003, 03:52 PM

hey guys, I'm no genius at electronics, but I want some opinions. I installed the e-codes a while back and just got some crazy bulbs for it (like 120/100 or something), but they aren't much brighter. Every now and then, while I'm driving with them on, they'll go bright (full strength), but only momentarily, and they'll go back to the dimmer stage. First I thought this was a bad ground or something, so I checked the battery terminals, and where the battery is grounded to the car (in the trunk), but that's not it, so I'm starting to think I need a higher amperage fuse because I'm still running at 12v but I'm trying to draw more watts (good old ohms law that I'm not at all familiar with). The confusion on my part is, I would have thought the bulbs would blow the fuse, instead of just going dim... could this be something else? Thanks ahead of time.

tecqboy · #2 11-30-2003, 07:26 PM

Well sir, I can't explain why your lights are not maintaining the proper brightness, but the problem is not likely to be the fuse unless it's corroded in it's socket. What is likely is that the new lamps draw more current than the primary wiring circuit can handle. That includes the actual wire gauge as well as the lamp switch. So, the way to find out is to measure the voltage at the lamp itself. It should be about 14 volts with the engine running. If it's lower, like 11 or 12 volts, then the voltage drop in the wiring is too high. You may need to replace the wire with heavier gauge. The larger the wire ( lower gauge number: #12 is actually heavier than #14 ) the lower the resistance. Lower wire resistance means more current to the lamps.

4NDELIT · #3 11-30-2003, 08:05 PM

hrm... forgot to mention something. When the headlights go bright, so do the gague lights, and I can hear the fan (like AC or heat) spin up a little. I think it's my alternator... any way of checking the output of the alternator?

nhodges · #4 12-01-2003, 04:23 AM

Sounds to me like you have something loose. Check your battery connections and your alternator ground. This could also be a voltage regulator problem.