I have a 2000 Toyota Avalon grande. Does the antenna lead from the radio screw off the motorised antenna?

A Toyota Avalon radio is bolted in place in the dashboard in order to prevent theft. If you want to replace the radio with a more updated stereo or an in-dash DVD player, you'll need to unbolt the old radio. The bolts are concealed by the dashboard's trim panels, and there can be one or two other objects you'll need to temporarily remove as well.
Step 1 Shut off the power to the Avalon by disconnecting the negative battery cable.
Step 2 Pry off the central register panel above the radio on the dash. Use a trim stick or a flathead screwdriver with tape wrapped around the blade. With the register panel gone, pry off the dash trim panel that surrounds the radio. Disconnect the electrical connector to the clock.
Step 3 Remove the control panel for the air conditioner if it is blocking your way to the radio's mounting screws. Remove the front console trim over the air conditioning console, disconnect the mounting screws and remove the control panel.
Step 4 Disconnect the mounting screws to the radio using a small hex wrench. Put the screws aside in case you can use them to install the new stereo or other device. Pull the radio out of its space to find the electrical connector and antenna lead in the rear of the unit.
Unplug the electrical connector and antenna lead, and remove the radio. These connectors will be used with any new radio or stereo that you'll install in the old radio's place.

two places if it is a power antenna on front of car look under wheel arc.
or
at back of radio

Only the electric wiring diagram has 360 pages. Impossible to post anything of that here. Sorry

check the antennae cable into the back of the radio to be certain it is firmly plugged in

I would check the connections on the grid, if they are ok you have to live with yagi effect.

The amp should have it's own inline fuse but if there is no sound it could also mean the radio has died or antenna is disconnected. Any stereo installation shop can find the problem without too much cost.

I had the same exact problem. Toyota changed the Amolifier that improved sound quality but not the FM Reception.

THE HARNESSES CONNECTING ANTENNA TO RECEIVER (TWO OF THEM) HAD IAASUES. REPACING THEM FIXD THE ISSUE. FM RECEPTION EXCELLENT NOW !!!!!!!

Check this for 1996 Toyota Avalon Car Stereo Radio Wiring Diagram Radio Constant 12V+ Wire: Blue/Yellow
Radio Switched 12V+ Wire: Gray
Radio Ground Wire: Brown
Radio Illumination Wire: Green
Radio Dimmer Wire: N/A
Radio Power Antenna Trigger Wire: Black/Red
Radio Amplifier Turn On Trigger Wire: N/A
Front Speakers Size: 5 1/4" Speakers
Front Speakers Location: Doors
Left Front Speaker Wire (+): Pink
Left Front Speaker Wire (-): Purple
Right Front Speaker Wire (+): Light Green
Right Front Speaker Wire (-): Blue
Rear Speakers Size: 5 1/4" Speakers
Rear Speakers Location: Rear Doors
Left Rear Speaker Wire (+): Black
Left Rear Speaker Wire (-): Yellow
Right Rear Speaker Wire (+): Red
Right Rear Speaker Wire (-): White

Hope helps (remember to rate and comment this free answeer).

this is usually caused by a defective antenna ground or a disconnected antenna lead at the back of the radio