How can I hook a color arcade monitor to a B/W game (Space Invaders)?

[quarterback]

I thought I had seen a post somewhere describing how this could be done (by connecting a couple of the wires together or not connecting a couple or something along those line).   
Anybody know how to do this?
Thanks
qb

[elvis]

A black and white monitor is just a 1-gun monitor (Luminance only, instead of R, G and B guns).

Technically speaking you'd need something to take just the luminance ("brightness") out of the signal and send it to the monitor (like a RGB->Y/C converter, and then just use the Y part?).  I don't think you can just simply mash the RGB signals together and use them.

[quarterback]

I found the thread where I had seen this mentioned.   It's here

In the 2nd post, pcb says

I've used standard RGB monitor on SI boards, so SID should be close.  What I had to do was pick up the sync before it was combined with the video out signal, and hook R,G & B up to the single video output signal. Makes a very nice B&W display on an RGB monitor.

So, my question now is "How do I 'pick up the sync' before it gets combined with the video out signal?"

I've PM'd pcb about this, but if anybody else can help me out here, I'm all ears.
Thanks
qb

[Ken Layton]

You pick up the sync before it's combined on the game board. You'd have follow the board schematics to see where at that point it would be. Also, if using a color monitor, you'd need to install an isolation transformer for the monitor as the original B&W one had a transformer built into it's own chassis.

[quarterback]

Thanks Ken, I'll check out the arcadedocs manual I have to trace the sync