Non-Functioning Tail Light

[schrocketeer]

May I please have some hints where to look for a non-functioning tail light? 1985 K100RT, all stock, rode 80 miles in the last 4 weeks.
Tail light bulb is good, brake light works - activated by either front lever or rear pedal. Just cut back clean and re-soldered all 4 wires in the ignition switch.
Everything else works (engine, hi/lo head lights, turn signals, emergency flashers, horn, kill switch). Always on a Battery Tender when not being ridden.
Disconnected, sprayed electronic contact cleaner at the Bulb Monitoring Unit (in Relay box) and the Right Hand Switch (under gas tank) connectors.

[daveson]

If the park light above the headlight doesn't work when turning the key to park,  maybe look at your  recent work to the ignition switch. 

If it does work I'd use a test light to check for power and earth to the tail light bulb, and clean the bulb contacts.

[K1300S]

Step one..... Check for 12v at the bulb socket.

[The Mighty Gryphon]

Did the problem start when you rewired the ignition switch?  That may be your best clue as to where to look.  Did you clean the inner parts of the switch as well?  They are known to get dirty and cause problem; there is information here on how to disassemble and clean the switch.

If the parking light works, try a different bulb.  It wouldn't be the first time a bulb and socket didn't work together.  If that doesn't work trace back checking for 12v at all the connections back to the ignition switch.

Like Daveson, my money is on the ignition switch.

[schrocketeer]

Update, zero volts at the tail light socket. Putting the tail light bulb in to the brake light shows the tail light bulb is good. Putting the good brake light bulb in to the tail light socket shows nothing.

[schrocketeer]

What is supposed to happen when you switch to the first position on the key (Parking Lights).

In the three years I've had my Brick, nothing has ever happened with the key in that position.

[Laitch]

What is supposed to happen when you switch to the first position on the key (Parking Lights).

The parking light in the headlight nacelle and the taillight get lit and you can withdraw the key.

[rbm]

Check the state of Fuse 2.  Make sure the fuse is good and the socket into which it is inserted is also working properly.  If you don't register a voltage on the front parking light with the ignition key in "P" position, then its a possible ignition lock problem or fuse 2 problem.

[schrocketeer]

In the ignition switch, after I jumpered together the Gray and Gray/Blue wires, the tail-light works, all the time, with the switch in the On position.
Oddly, the front parking light is intermittent with the key switch at On.
Nothing happens front parking light nor rear tail light with the key switch in the Parking position.
This attachment is the test jumper. I hard soldered in a jumper between Gray and Gray/Blue.

[The Mighty Gryphon]

Have you cleaned and lubed the internal bits of your ignition switch yet?  It looks like yours is on the way to stranding you someplace when the main contacts stop contacting.

[rbm]

TMG is right.  By soldering the jumper in place, you've bypassed failing contacts in the switch for the parking light circuit.  However, there are still contacts for the main ignition circuit that may fail in the future.  You've got to refurbish the switch.

[Laitch]

 Use the link here for instructions to get inside that switch.