Sounds like the 3 wires you mention should have a connector on the end that plugs into the distributor cap. The connector is index and will only plug in one way. If you do a search you will find many posts on installing the HEI distributor. What it comes down to is you need to replace the wire to the old coil with a 10 awg wire. The yellow wire for solenoid is no longer used, it was the 12v bypass for starting. There are two connection on the distr cap one marked bat. and the other marked Tach. That should get you into the ball park.

Larry

I don't own a vehicle that isn't old enough to drink.