Does anyone know how to disconnect the tach pickup from the engine?

My tach started bouncing wildly recently and though I first figured it was the amp going bad (as the are wont to do) but it turns out the gray cable from the pickup to the amp got a bit loose and was rubbing against the AC compressor pulley. I need to get it out so I can either patch it (hopefully) or replace it. Does anyone know how exactly this thing comes off?

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'81 300TD Wagon 355k (Miss Diesel)
'83 300SD 180k
'84 500SEL 190k (Parting it out)

To answer my own post, it was fairly obvious once I washed the area around the pickup. It had been covered in black crud and I couldn't see the little 8mm nut that needed to be taken off.

The nut is a pain to get to, however; I had to remove the waterpump/fan pulley to I could reach in with the little wrench. Well, even then I'll admit I couldn't do it - I spent a couple hours cursing the damn thing before a friend with more deft hands than mine showed up. He had the nut off in less than sixty seconds .

Patched up the cable (new ones are $50!), had my friend put it back on , and it seems to work fine once again.

__________________
'81 300TD Wagon 355k (Miss Diesel)
'83 300SD 180k
'84 500SEL 190k (Parting it out)