Here are skyjacks suggested possible causes for this issue:
if you need better detailed info go to their website and go to the manual section and download manual 'part number' 118941.

1. Loose or broken wire #07 from base terminal block
(TB-1) to platform emergency stop switch (S4).
2. Open or defective platform emergency stop switch
(S4).
3. Loose or broken wire #7A from platform emergency
stop switch (S4) to key switch (S3).
4. Open or defective key switch (S3).
5. Loose or broken wire #8 from keyswitch (S3) to battery
charge indicator (BCI).
6. Loose or broken wire #8 from platform keyswitch
(S3) to joystick enable switch (S7-6) (ANSI/CSA
only).
7. Defective joystick enable switch (S7-6).
8. Loose or broken wire #8 from battery charge indicator
(BCI) to LIFT/DRIVE select switch (S5)
(CE only).
9. Defective LIFT/DRIVE select switch (S5).