Olympus OM10 and OM20 with Metz 45 CL-4

I have a Metz 45 CL-4 and an Olympus OM10 and OM20. I have read this (https://www.photrio.com/forum/threads/olympus-om-cameras-with-metz-45-cl-4.81502/) but it doesn't give me the answers I need.

The flash has TTL mode, but from what I have read, the OM cameras do not. So I guess that means that if my camera is set to F8 at 1/30th sec, say, the flash needs to be set to F8, or 5.6 say, to act as fill in light?

I can attach flash to camera with the lead seen in the picture below, which I gather is the cable plugged into the 'synchro socket'. Is that the correct way to use it, or do I need one of those special SCA adapters that sits on the top, like I have for the Nikon F5 (SCA 3000)? If so, which one do I need, and what is the cable attached for?
Thanks

You are correct that while the OM-20 uses TTL off the film metering for regular exposure settings, it doesn't offer TTL off the film flash metering. That means either manual, guide number based exposure calculations for flash use, or using the flash's built in auto exposure system.
The Metz flashes have really good built in auto exposure systems. I would recommend you use that.
You have the cord set up right.
The manual for the flash (available on Mike Butkus' site) describes how to use the auto exposure system - you set the white line opposite the green number, set your camera aperture to the green number (or one stop smaller for fill) and the flash's auto exposure system adjusts the flash output for you.
You need an OM2, 2n, 2s, 4, or 4T plus the Olympus compatible SCA module for TTL use.

Thanks Matt...you've answer my queries, again Good man

The Olympus TTL Autocords are meant to be used with Olympus bodies that support TTL flash automation (not OM-10/20).
You can use a simple PC connector to trigger the Metz 45CL flash unit. Instead of the PC connector cord, when the Metz SCA-300A connecting cord is used with the SCA 321 module for Olympus, the flash dedication features of your bodies will be activated, including auto shift to X-synch speed when flash is on, and enabling the flash ready/flash confirmation light in the viewfinder (but without TTL flash automation). The SCA 300A has a special connector that mates to the SCA321 which is then mounted in the camera hotshoe.

Regardless of use of the PC connector or the dedicated SCA connector, set the Metz to your film ISO and put it into the flash photosensor Auto mode (not in the TTL dial mode), by setting the dial on the top of the Metz so that the white arrow points to the selected lens aperture green number.
(Or set the dial on the Metz to a larger aperture than actual, if you want fill at a reduced level of intensity from ambient).