That's the control module for an early generation anti-lock braking system for the rear brakes only. See: https://www.aa1car.com/library/abs_kelseyhayes_rwal.htm I have a 1991 Dak and either the module is bad or the ABS solenoid that is plumbed into the rear brake line is bad. The emergency brake light (red) stays on to indicate that there is a problem. You can use the paper clip trick to get the ABS Control unit to blink out the error code. Refurbished ABS control modules are available but a rebuilt solenoid valve with the electrical connector for your make and model Dak is hard to find. The little truck brakes work fine but there is no ABS action on the rear brake circuit. It's like driving old school