There are differences between a 1979 ford mustang trunk or hatch lock than later generations of the Fox body Mustangs.
Regardless of what people tell you on eBay or any parts store. Most these people are going off of what a vender is telling them or supplied information from an alternate source. I will tell you that you will need to make modifications to the lock in order to make it work if it's a re-manufactured part.
If you can find OEM you'll have less time invested.
This is the lock retaining clip later mustangs don't have. I am making a new gasket for it.
The dirty Lock is the original for the hatch. You can see their are some differences and modifications will be required to make the new lock work with retaining clip.
Additional differences found
Here you can see missing machining needed for the retaining clip to be used.
I will fix this manually, because I don't have faith in finding anything different and for some reason most of the salvage yards I have dealt with in Wisconsin have smashed the early Fox body Mustangs treating them like they are a dime a dozen. Ignorance is bliss.
This is where an air file pays for itself. These little fabrication jobs would be time consuming without this tool.
Harbor Freight sells them cheap and they work awesome.
Wrapped tape around to reduce chance of debris in lock.
Match that gap was the goal and it was success.
Air file worth it's weight in gold.
Test fitting the retaining clip.
Side by side comparison
More Machining to match original.
Retaining clip is pop riveted in place. That should be your last step.
source: Fox Body Mustang Restoration http://ift.tt/2zgjhYe