79 Spider Oil Gauge Sensor Removal

I use a bicycle wrench - stamped out of 1/8" steel. It can be bent or cut for best access. Once loosened ~ 1/4 to 1/2 turn it will probably come off the rest of the way by hand. The senders I've seen have either a 17mm hex or 14 mm hex.

You can use a "crow foot" wrench on it but there is no firewall near the oil pressure senser.
You may be removing the wrong one. I think the one you are describing is the low oil pressure light switch.
But then again I may be wrong. Won't be the first time..

I believe that they make a special size socket that will fit over the end for removal because a wrench is really hard to get in there and do any good if you get it in there. You will want to use some penetrating oil beforehand and I put a vise grip over the end horizontally and put a second vise grip attached to the handle 90 degrees up vertically and was able to get it loose that way.

What Eric says in post #2.

The gauge sender IS the one nearest the firewall. A real bugger to get a spanner in. I disconnected the battery (the starter is too close for comfort) and cut a standard spanner in half. Works a treat. As already stated once you have moved it half a turn (anticlockwise) it should come off easily by hand. The existing one I removed had a 17mm nut holding it on, the replacement had a 19mm nut (later model one) and the eventual correct (early) had an 18mm nut! typical Alfa eh!

Problem is you can get a wrench on it but the area is so tight you can't move the wrench. That is what I found anyway.

Yes you can if you saw a standard wrench in half. Easy to saw one in half (although you sacrifice the wrench) I bought a standard sized wrench for 3 Euros and sawn in half it is only 10cm long. Not a lot of room but enough to turn the nut half a turn before hitting the firewall. If necessary you can turn the wrench through 180 degrees and get another half a turn in. Worked for me a treat.

You must have small hands.

Big hands with scratches on after changing the sender!!! It is a crazy place to locate a sender. OK with the engine out but a bugger when installed in the engine bay. My original sender was faulty so I ordered a new on. Sadly it was the wrong one so had to order another replacement. I got quite expert at changing them out!
BTW remember to aneal the copper washer before fitting the new gauge. The washer fits between the engine block and the sender to prevent oil leaks.

2 choices. You can either file a your wrench to the correct thickness, or you can take Eric's suggestion and buy a bicycle wrench.

Or buy a set from Home Depot Husky Thin Head Access Wrench Set (6-Piece)-H100THCW6PCSM - The Home Depot

After you've done it 9 or 10 times on several different Alfas you won't think it's a big deal.

I don’t remember having an issue, I do remember though that my old sender was a different mm wrench than the new one.
it was finicky to reach but it didn’t take much to get it off