What am I doing wrong? MIL light issue.

[trunknuts]

I took the brown/white wire coming off the PCM (2005 5.3L engine) and wired that to one side of the light on the dash. The other side of the light was wired to a 12V feed. When I turn the ignition on the light never comes on. Shouldn't it come on upon startup? The only time the light has ever come on was when I tried to start the engine with a weak battery. It came on and only went away when I charged the battery and started the engine. Any help getting this to work will be greatly appreciated. Thanks.

[NITROUS]

Make sure in your DTC's that P0650 is unchecked with 1-MIL on second error. If so turn the light on with your scanner for verification. If you went directly from wire 46 to the light you should be in good shape. And yes, the light should come on with the ignition on.