Date registered: Dec 2003
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RE: 300TD electrical problem
I'm no electrician so take it for what it's worth. Basic troubleshooting rules always apply and one of the first is that one indication may have nothing to do with another. You may have multiple problems. I doubt the amperage necessary to operate the gauge can blow a significant fuse like the horn fuse. Likely, you're seeing the failure of the fuse as a twitch in the gauge. What other functions are served by that fuse? Is there a problem with any of those components before the fuse blows? Also, the fact you must place your foot on the brake pedal to get the turn signals to function indicates you probably have a bad ground somewhere.
I'm not a Mercedes expert. Or any automotive expert for that matter. The first place to look on an older car such as yours is to ensure your ground is sufficient and still functioning. I suspect Mercedes placed various grounds on the chassis of the car. Get underneath the car and ensure they're still intact. If they are, ensure they're tight and attached to a rust free surface. How about your battery cables? Have they been replaced lately? If not, buy some new ones. I've seen a cable that looked like new on the outside but was corroded almost all the way through on the inside. Get good cables. If you pay $4.99 at autozone, you got the wrong cables. Especially for a diesel.
That should be enough to get you started until someone who knows what they're talking about responds.