I edited my post, now showing a speedo. Reposting below.

This is all from memory so take this with that caveat.
Here is a picture of the back side of what I believe is a 74 speedo.

https://cimg9.ibsrv.net/gimg/rennlis...526a3de5ba.jpg

Does yours look the same? Here's a link to the site where I got the picture. https://rennlist.com/forums/parts-marketplace/1037101-fs-porsche-speedometer-odometer-gauge-for-1974-1975-911-a.html

If yours looks like this, it appears that all the holes are the same size and the bulb carriers appear to be the same as well. You might let us know if the parking light hole has a "lip" around it, as that would indicate the guts of the carrier are gone but the brass shell is still inserted. You can see the lips of the bulb carriers in the picture.

Ah, thatsa better. Just like mine, but i don't have it in front of me. However, as I recall from earlier this morning, before coffee and before going to work, all 3 orificies look the same on the speedo back surface. If you use a drill bit as an index, you can feel that the indicator hole is slightly tighter than the other two. This is consistent with the problem of the bulb holder fitting the two "larger" ports, but not the one I'm want it in. When i get back home in a little while (gottta hallway pass b/c of the "inclement" weather here in Houston....please hold your laughter if you live north of here!) I'll see if the current in situ bulb holders fit, tho' it won't tell us much, really. thanx s

My 2c would be some prior owner tried to remove it and yanked it by the wire, as ossiblue stated. That resulted in him (or her) pulling out the base of the bulb holder, leaving the brass bolb holder housing still in the gauge. You may need a pair of needle nose pliers to pull the remnants out. The hole in the housing is the same for all the bulbs, even the 2 wire ones.

That makes sense to me. Lemme look at that more carefully when i get home. thanx for all of your thoughts. s

CASair has stated it well. The shell of the holder is soft and a PO could have pulled out the guts, then tried to remove the shell but instead only succeeded in pushing it further in. That could account for the failure to replace it.

One other possibility.

The OG bulb holders clearly have the wire attached to the base. If you had to replace the holder, did the new one have a spade connector? If so, it may be just slightly oversized compared to the OG and that's why it does not fit. Without knowing what you are looking at, this is only a guess, but anything can be possible.

Here's the exact holder I bought....wire comes straight from the base.

https://www.ebay.com/itm/Porsche-356-911-912-Instrument-Bulb-Holders-2-C-103/162759508723?ssPageName=STRK%3AMEBIDX%3AIT&_trksid =p2060353.m2749.l2648

if not too, too cold i'm headed out to the garage to take a peak. Been too whimpy to head out yet. s

I tried to take a few pictures, and they're worth about two words...lousy shots. It's hard to take a good photo of the difference between the holes...but I tried. The red arrow shows the "good" orifice that will take the new bulb holder, as well as it's assigned old one. Note the groove in the bore. The lousy picture with the yellow arrow is the errant hole for the parking indicator light. There is no groove in the bore. There looks to be sleeve (? part of an old bulb holder) but it's pretty even and symmetrical; not ratty looking. Will not come out despite multiple good efforts with a curved pick. Don't think needle nose pliers will be better. The guy at Nichols Speedo shop in Greensboro N.C said he could get it out, so I may just send it back there. They were very fast and professional when i sent it in for its initial repair. Highly recommended. thanx stevehttp://forums.pelicanparts.com/uploa...1516157041.JPG
http://forums.pelicanparts.com/uploa...1516157041.JPG

Again, I'm operating from memory so this is just speculation.

I believe the hole for the parking light has a sleeve or internal tube that restricts the light to just the lens on the face of the speedo and keeps it from spreading out around the gauge. The gauge lights do not have that because the intent is for the light to radiate outward and illuminate the face of the gauge. This may explain the different look of the holes as well as the appearance of a sleeve/tube inside the parking light hole. Regardless, the standard bulb holder should fit.

Though your pictures are blurry, there appears to be something inside the bore of the parking light hole. It appears exactly where the yellow arrow ends. Is that something, like corrosion or some kind of bump in the bore, or is it just an illusion from the photo?

Bottom line, you may need to send the speedo out to the shop, along with an explanation of your problem, and let them deal with it. They should know why the holder does not fit.

got 'her boxed up and ready to ship out. i'll report back. was thinkin' of turning a drill bit in there very, very slowly, but I don't want to mess up the gauge, and then, still have to send it off for more repairs. thanx again for your thoughts. steve

Reporting back...the guy called from Nichols speedo shop. He took the speedo apart and found nada, nothing in that orifice...no broken parts, etc. So, it's back to square one, as far a bulb holder that fits that socket. The picture submitted by "Ossiblue" is just like mine, except where he has the correct green/white wire going to a bulb holder that fits, mine won't fit....as noted it fits the other orifices, but not that one. I'm lost on what to do next. thanx. steve

A friend who has a gazillion Porsche parts sent me a bulb holder that fits perfectly...pictures enclosed. The ground is a spade/contact that is along the side of the holder. Single wire. Unfortunately, I think it's defective (but I need to do more work on it.) Anybody know the part number for this, or a vendor? thanx steve

ADD: sorry about the fuzzy picture, but the red arrow shows the ground contact.http://forums.pelicanparts.com/uploa...1517443155.jpg
http://forums.pelicanparts.com/uploa...1517443155.jpg

OK, here are better shots of the bulb holder that fits. still would like to know who might have these. thanx stevehttp://forums.pelicanparts.com/uploa...1517539205.jpg
http://forums.pelicanparts.com/uploa...1517539205.jpg

Can you tell us the date stamped on the back of your speedo housing? My thought being it's a later housing as that bulb carrier seems to be a later type. Just guessing.

argggh. the bulb was installed this AM...so, it's too late to find the date, but i'll say this...I didn't know that the ground spade must be folded down at 90° to contact the back of the speedo. I thought it made it's contact inside the housing orifice, but it doesn't. Took me awhile trying to figure that out!

Now that it's back in the car and everything works right, I HIGHLY RECOMMEND Kevin at Nichols Speedo in Greensboro, NC. He did an excellent job, fast, helpful and friendly. Knows these gauges inside and out.
NSI Fleet:...Automotive, Marine, and Navigation Instrumentation

After the comments I saw about the highly vaunted folks on the west coast, I'm ecstatic I made the decision to send to Kevin at Nichols. I had the speedo back and fixed in less than one week. USPS trumps (pardon the pun) the others every time. steve