My tail/brake light is not working on my 1999 intruder. They were working fine last week but not now. when I turn the key to the rear "P" position, the brake light only works, not the tail light.

try the switch on the rear brake pedal, could be naff, or need a good clean, does it work on the front brake??

Replace bulb

The brake light side of the bulbs is powered by the brake switch and travels thru the turn signal switch.
If the third brake light works, I would guess the problem is in the turn signal switch.

just look for the blackened/burned pin on the rear light plastic connector and sand it down to re-establish a good electrical connection and save yourself $800 big ones on replacing the multiswitch.

CHECK TURN SIGNAL FUSE.IT COULD BE BLOWED OR YOU HAVE FAULTY TURN SIGNAL SWITCH.BECAUSE BACK LIGHTS AND TAIL LIGHTS SHARE SAME CIRCUIT WITH TURN SIGNAL SWITCH.

CHECK TAIL LIGHT BULBS.IF BULBS CHECK OUT GOOD PROBLEM COULD BE CORRODED BULB SOCKETS OR BROKEN LOOSE WIRE IN CIRCUIT.

Most likely a fuse or circuit breaker. Check your fuse box for a blown fuse. I assume your brake lights still work. Yeah, that's scary alright. You were lucky not to get a ticket.

It mught be the bulb that needs replacing or else check the wiring to the bulb for continuity in case there is a broken or snapped bit.If you have a voltmeter then you can test the voltage reading at the point of contact..Sometimes rust builds up and a simple cleaning would solve this.Hope this helps.

I have taken my car to many shops to solve this problem. Long story short your tail light has a bad circut and entire lamp must be replaced. (Lamp cost approximate $130.00)

Having the sa but haven't replaces the brake switch. The owner's manual for my 99 accord indicates the the fuse is located behind a panel that is viewable when you open the door on the driver's side. There is a panel that you remove (pull off) to expose the fuses. The brake light fuse is the third one from the top on the left. 7.5 A