Yes, pins 2 and 3 will go out to your MD. So pin 2 will have 2 cables attached - the (-) from the battery, and the (-) going to the MD.
Your MD *should* have a female DC power plug (if it doesn't, the rest of this post is meaningless).
You'll hook up a male DC power plug to the battery pack. DC power plugs have a ring and a tip. Near the plug, or in the documentation, it should indicate whether the ring is (-) and the tip is (+) or vice versa. It's usually ring (-), tip (+). The symbol on the unit usually looks like a dot surrounded by a circle. The dot represents the pin, the circle represents the ring.
The easiest way is to wire up the following RS cable to your VR:
RS Female Adaptaplug Socket Cable # 273-1740
Then, find the right sized adaptaplug at RS to fit your MD. I usually take it in and just see which one fits - easier than measuring the inner and outer diameter of the DC plug and trying to match that way.
The adaptaplug just slots right into the cable above - no more soldering. But check to make sure the polarity is correct! The adaptaplug can go into the above cable 2 ways - one way will be ring (-), tip (+) and the other will be ring (+) and tip (-). If you don't have a multimeter, you should get one (they're cheap and easy to use).
The slightly harder way - but sometimes a more secure fit between DC male plug and female receptable on the unit - is to get a higher quality DC plug elsewhere (sorry, don't know which one b/c I don't know which your MD takes) and wire the DC plug directly to the battery cable (again making sure you have ring/tip polarity correct).
When I first learned how to do this, it seemed complicated. Then I actually did it - it's really easy to do. Honest!