95 blazer 4x4 wont go in 4 high?

95 blazer when in drive wont go in 4 hi. light wont light up. in nutural it goes in 4 low but when i push 4 hi in nutural it flashes & goes back to 2 hi. if i disconect the battery for a while then hook it back up it goes in 4 high some times. after a while it wont work again. the ball under batery is good & working. all vacume lines hooked up. switch in dash it good. sometimes when i put it in 4 low both lights light up & sometimes none light up.

95 blazer when in drive wont go in 4 hi. light wont light up. in nutural it goes in 4 low but when i push 4 hi in nutural it flashes & goes back to 2 hi. if i disconect the battery for a while then hook it back up it goes in 4 high some times. after a while it wont work again. the ball under batery is good & working. all vacume lines hooked up. switch in dash it good. sometimes when i put it in 4 low both lights light up & sometimes none light up.

Have you checked for codes?
Which transfer case do you have?