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Where have you looked for "steps?" Unless instructions came in the box with it, there probably aren't any instructions anywhere, so you'll have to figure it out for yourself.
These lights were typically located on the hood about a foot or so up from the trailing edge on the driver's side.
Here's where it's located on my '78 Toronado, and I think this is a typical location.
If I'm not mistaken, these have a mercury switch in them so they only illuminate when the headlight switch is on and hood is raised. So you'll have to wire it to a source of headlight-switched power (perhaps tap into one of the parking lights). The ground is accomplished automatically through the housing when you mount it to the hood, so there is no need to worry about a ground wire.
Since these were standard equipment, I think, the wire for it might already be there somewhere under the hood (and the mounting holes might already be there as well). Look for a wire in this area of the firewall that's not connected to anything and test it with a test light or voltmeter to see if it's powered when the headlight switch is on.
It looks like you've got an aftermarket one as the wiring plug is different than what the 1972 Cutlass had. If you want to splice it into the wiring harness you may need to change the connector. Also the factory had an extra tab where the plug bolts to the hood. The tab has teeth on it to help make a good contact for the ground. If you don't have that you may need to do something to be sure it maintains a good ground. John
The under hood light gets its power from the tail light fuse and its wired to the brown wire that feeds the front marker and parking lights. It will only come on if the headlight switch is on.
