To find it:
1. Under the dash: Look behind the instrument panel, usually near the steering column. You might need a flashlight and possibly have to remove some panels to access it. It's often a small, rectangular box with two or more wires connected.
2. In the fuse box: Locate your fuse box (usually under the dash or in the engine compartment). The flasher relay might be integrated within the fuse box itself or in a separate holder within the box. Consult your owner's manual for a fuse box diagram to identify it.
If you can't find it using these locations, consult a 1985 Ford E-150 repair manual or a wiring diagram specific to your van's year and model. These resources will give you the precise location and show how the flasher unit is connected to the vehicle's electrical system.