It's so simple that I'm almost ashamed to publish this as an instructable, but sometimes it's the small things that can make life easier...
What you need:
- A (small) plastic clothes-pin
- 3 inches of copper wire
- A foot of red and black cables
Step 1: The Contacts
Cut the copper wire in two parts and wrap each wire around the the upper part of each part of the jaw on the clothes-pin. They only need to be tight enough to stay put while soldering. After the soldering the wire will have melted into the plastic of the clothes-pin and will be securely fixed.
You need to be a bit careful with the heat though, is the wire sinks too deep into the clothes-pin it can't make a connection to the battery and you'll have to start over with another set of parts.
Keep the jaws open while soldering so that the other jaw doesn't get affected by the heat when soldering.