Power for Reverse lights

[money pit]

I had problems with the engine starting in park and neutral. I replaced the NSS with an NOS switch (after trying 2 after market units). I also replaced the wiring harness to the NSS. I checked for power at the firewall, with the car in reverse and the engine on. There's no power at the firewall. The fuse is good. I checked the harness. There's continuity on the wire that goes to the NSS when the trans in reverse and no continuity when in other gears. Is there supposed to be power at all times at the firewall for the reverse lights and the care is in reverse when the power is on? 

[Filthy Filbert]

Going from memory, and not looking at a schematic, there are 3 wires to the NSS

One has power when the ignition is on.
One goes to the starter solenoid--the NSS supplies power to this wire when in Park or Neutral
One goes to the reverse lights--the NSS supplies power to this wire when the transmission is in Reverse.

If you have no power going to the NSS with ignition on, start chasing that part of the circuit to find where you're losing power.

[money pit]

I thought that the power for the back up lights comes from the firewall, down to the switch. When the trans is in reverse, the switch closes completing the circuit, turning on the lights. I'll take a look at the schematic.  Thanks

[money pit]

I found the problem. there was a short behind the fuse box. The fuse box was not connected to the bulkhead correctly.  Thanks.