Hello Judy,
if what you saw on the display was AL 05 then this deals with the brake circuit.
The dash would display AL5, the controller would flash on it's LED 5 flashes, or the handset would indicate what the alarm is.
The condition is: Electric Brake does not release or remains released at all times.
The truck response: Traction and hydraulic functions disabled.
Possible causes:
-Damaged or loose electrical connection to brake. Verify electrical connection between electric brake and controller.
-Check brake coil for correct coil resistance. Disconnect brake. Measure brake coil resistance in both directions. Coil resistance should be 14.3ohms.
-Damaged fly-back diode at brake. Check coil resistance. Short circuit measured at brake connector may indicate a damaged diode. Cut(disconnect) one lead of diode and check with meter. If damaged, replace diode.
-Damaged controller. Activate the brake switch. Use voltmeter to measure voltage on wire 2C and 17 with brake connected in circuit. If both measurements are 24v and the alarm is displayed, then controller is damaged.

Note: the brake coil harness connects to terminals B-16 and B-5 on the controller plug. Wires in the harness are wires 2C and 17 which are Blue and Brown, wire 2C is brown, wire 17 is blue.
Also check the brake switch and make sure it is operating properly. (i would confirm this first). There are other things to check the tblshooting does not mention but we won't go there just yet. :o)