I had the same issue when I took mine apart until I pulled the yellow lever out.
I think I was only able to clean the contacts and grease them.
One of the contacts was recessed indicating it had been heating up at one point.
Hence the installation of the extra relay I added
Be careful it has a little ball bearing with a spring behind it.
But the hard part is putting it back together without launching that little ball out

Luckily I had a little box of that size in my Bicycle parts stash.
I think i lost 3 of them before I got it back together. 8-)