This Old Benz Needs Grounding

Dear Car Talk

Dear Car Talk | Sep 27, 2018

Dear Car Talk:

I have a 1979 Mercedes-Benz 240D that sat for about a year because the injection pump began to leak. I eventually was able to find an inexpensive injection pump and install it. I also put in new glow plugs, a new starter and a new battery. I checked all of the fuses and cleaned the fuse holder.

But now when I turn the key, there is nothing. The dashboard lights won't even come on. I had no electrical problems before the car stopped running. I would appreciate any ideas you have about what I should do next. Electricity is the only class I failed. Thank you. I love your show. -- Ed

I think you might have failed "Car Selection," too, Ed. But we'll leave that aside for now. You're getting absolutely no power when you turn the key. That's good. It's good because it's easier to diagnose than an intermittent electrical problem.

My first guess would be that you've got a bad connection at the battery or a bad ground. Every electron that leaves the battery eventually has to return to the battery. So if Eddie Electron leaves the positive terminal, and goes to the ignition switch, then to the starter, it then has to leave the starter and travel through a ground wire to the engine block and the chassis, where another ground wire brings it back to the negative terminal of the battery.

If it buys a one-way ticket and fails to make that round trip, you don't get any power. Nada. Zip. So start by testing the battery. It's new, but test it anyway. And make sure the cable connectors are tight and free of corrosion. If the battery is good, then you need to test the ground connections. You may have simply knocked off a ground wire, or a ground wire may have "completed" its corrosion process during the year this thing sat in your driveway.

If the ground wires are all connected, and not obviously corroded, have an assistant try jiggling them while you try to start the car. Have him or her jiggle all the wires under the dashboard too. If you turn up nothing there, test the ignition switch, which could be at fault. But my first guess is that you've got a loose or corroded ground wire.

When you finally do get the car started, Ed, then you can look forward to spending a weekend trying to bleed your new "inexpensive injector pump" and figuring out if the only reason it was "inexpensive" is because it leaks just like your old one. Best of luck.

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