When I took off my rear stoplight switch the metal arm with the hook was outside this tab on the frame. 

is the metal rod supposed to go thru the tab on the frame and fold the top of the tab over?

pics below click on image 

imgur.com/gallery/1975-dt400b-rear-brake-light-switch-cG8yRpQ

Thanks!!
 

I'm afraid that Imgur is no longer available here in the UK, so I can't see your photo or post any of my own!

Anyway, as I think my 1974 DT360A uses the same weird set up, I'll try and explain how mine looks.

The hook on the end of the switch (see first ebay link below) sits in the tab on the brake shaft (see second ebay link below, although this is pointing straight up, so you can't see the hole).

GENUINE YAMAHA PARTS - STOP SWITCH ASSY. DT250 DT360 DT400 1974-76- 438-82530-00 | eBay

438-27212-01 NOS Yamaha Shaft Brake DT250 DT360 S26y | eBay

The curve on the brake switch matches the contour of the swing arm and it sits inside the frame "cradle". There is no bending of any tabs.

I note that the shaft part number for the 1975/6 250/400 is different from the 1974 250/360, but the set up looks the same.

gr8uncle, can you see posts if they are posted as PICS instead of links from imgur? Just curious .

As far as I know, Imgur is the only one that shows up as not available in my area, so anything else I should be able to see what other members can see.

Here is a picture of the way I’ve got it routed. I posted it on YouTube so you chaps in the UK can see it. Thanks for the help!

youtube.com/shorts/FFP-ht8wu-I?si=aldsWQWG76TosXTE

Thanks.

Let's see if this works!

Edit - it might work if you copy and paste it into your browser.