If you want to knock out a lightning wyvern and have a decently leveled terror bird with a saddle, simply shoot the wyvern from the back of your terror bird(since terror birds appear to be immune to lightning damage). The only other thing you would have to do is dodge its bite attacks.
I got a level 150 lightning egg and I was so excited to hatch the egg...that when I went to put the egg down I accidentally ate it instead. :( ps4 users: R2 ISN'T GONNA DROP THE EGG YOU'RE GONNA EAT IT LIKE ANY OTHER EGG. REMEMBER THIS. LOGIC BEFORE EXCITMENT.