When down shifting one must depress the clutch place shift lever in neutral release the clutch rev the engine too approximately the correct rpm for low gear for the equal road speed depress clutch and then shift into low .
Al
Check the battery terminals,
there is a good chance where the wire goes into the clamp it is very crowded inside.
To check pull hard on terminal, it may come of.
I don't have a photo but you are looking for a pipe that is threaded on one end and crimped almost closed on the other also a spring that fits inside the pipe and a rod that goes inside the spring that has an large flat washer that will not go through the spring and has a ball end on the other end that hooks into mount on car frame.
Warm up engine lock brakes and yank shift into high gear with engine idling do not use a lower gear, should stall engine if clutch does not release.
Al