pgambr, your avatar says "S40", so have to assume it is 2004 or later.
Restating what some others have said.
From looking at Clymers:
The horn and headlight hot line is black/orange. On the other side of the connector that sits under the tank on the left side, it is orange. It is not uncommon for that connector to come loose when replacing the gas tank.
If the neutral light or speedo light works, you have 12 volts to the orange wire on the chassis. You can also check that wire on the connector for the ignition switch.
If you have 12 volts on the orange line, my suggestion. Pull the tank. Reseat that connector (and maybe spray it out with contact cleaner) and see if that fixes your problem. If not, check for 12 volts on the orange side of the connector, if there, see if you get it on the black/orange side.
While this is not a multi-meter, it is my weapon of choice when looking for voltage:
http://www.harborfreight.com/circuit-tester-30779.htmlIt has a needle point that you can poke through the insulation or worm into the back end of connectors, and the indicator light is in the handle.
I must disagree with HondaLavis. Ground is always black/white, never black.
(Except the wire that goes from the battery to the engine for chassis ground).