Non- MB, but a spark plug problem. Why would I show continuity between the cap and body of a plug? If I'm not mistaken I should only show continuity between the cap and center electrode. The metal body should be insulated from the center electrode by porcelain, correct?

I checked this with a back-up plug from another car, and show no continuity between end cap and body - except if I hold the leads to each with my fingers (then I'm getting continuity through me).

What could cause a plug to "short" like this? I'm off to get a set of plugs, but would like to know what killed this plug.

It sounds like the wire is touching somewhere.

Internal short. Bad plug. Happens.

Shorted plug...
 

An interesting question.... I had a plug in my tractor that stopped working last week after only 25 yrs of service, and I decided to try sandblasting it to see what happened... I hit it with the sandblaster for only a few seconds and it cleaned right up, looked like new, so I reinstalled it, and it works great again. I really wouldn't recommend this sort of thing to anyone, but it appears that the carbon buildup on the ceramic is what shorted this one out. I could make it fire by holding the wire about 1/4" away from the plug - I suppose this allowed a higher voltage to build up and then it fired across the electrodes instead of through the carbon. On another subject, I just pulled the head off my niece's corsica 2.2L 4 cyl. this afternoon, and it had some water seepage from the front water passages at each end. Nothing was warped, but the head gasket looked like there was movement on both ends. I'm thinking of applying a bit of silicone gasket maker just around the water passages where it was leaking when I reassemble it - I did that once on a cadillac 4.5L aluminum V8, and it held up well for years. Any thoughts on the efficacy of such a maneuver?
Richard Wooldridge
'82 300D/4.3LV6
'75 280C
'77 Jag XJ6L
'77 280Z