Greg -- I just did this job on my 'new' 87 last Saturday. I forget which colors went where on the clock, but the Volvo setup typically uses a 3 wire harness which plugs into the back of the tachometer. The tach has three male posts for the plug:

#30 = 12 volt positive, always on, to run the clock

#31 = ground

#58 = variable positive, to power the bulb.

I'm educated-guessing, here, but I believe a black wire was ground, a green was variable + bulb power, and the red was always 12 v. I may have the green and red mixed up.

You can share the ground for the bulb and the clock.

That thin pole *may* be the soldered ground attachment to the metal case from a post from the circuit board inside. I cut my clock apart two weeks ago to replace the capacitors as recommended in Rolling several issues ago, and I had to unsolder this post to slip the case off once I had cut it free from the bezel. Your VDO clock might be different than my Volvo/VDO version.

Rob