There are posts attached (welded) to the face of the firewall on 69 and 70 Mustangs on the engine compartment side. The subject of one of these retainers came up on another site recently so in response to that thread I went through pictures and collected and looked at what I could find related to the subject.
It appears that a number of different style retainers were used (have four so far) depending on what was being retained/secured, what assembly plant and during what time period. Have not do a in-depth look yet, may not have enough data yet to provide a complete picture, but wanted to offer some pictures and what I had found so far related to just 69 Dearborn findings
Here are a few pictures of them installed sorry they could not be much clearer or free of obstruction. They are a pain to take off without breaking them and were used for different purposes depending on Mustang and Shelby model.
Holding a speedo cable on a four speed car. These are reported to now be available in reproduction form.
Close-up of a flatter version most often found, so far, retaining wire looms in this case for the neutral safety and back up lights
They can also be found used elsewhere on the firewall depending on model, time period and plant. Lower one is broken likely by someone jerking on what ever was in that clip. These appear to be faded from exposure to the sun. Looks like its possible that this was an Oklahoma yard picture
During the production years the flat style of wire strap/retainers were sometimes used. Similar style (though possibly different) to those are like the style found at the drivers side rear of the engine compartment that hold the windshield washers hoses to the firewall. This one was being used for the speedo cable for a four speed car like the first picture above.
