Question about 1984 Honda VT 500 C Shadow
If the tail light is working, then look at the sensor, it is placed under the seat( it is a small black box 2x1,5cm) disconnect and clean contacts. Also put some contact spray in other wire joints.
Sorry for my English
Posted on Apr 23, 2009
I believe that Alex is talking about the "idiot light" labeled "Tail light" on the dash of his 84 Shadow. When this idiot light is lit, it is supposed to mean the tail light has burned out. My 85 VT700 has a problem where that idiot light fades on and off even though the tail light is working fine. If I apply the brakes (an brake light comes on), that idiot light goes out.
I have not solved the problem, but I did investigate this about 2 years ago. The Idiot light is connected to a small rubber encased box about 2 by 2 by 2 inches located under the tank, near the air filter on the right side. Several wires come out of that box. One wire provides power to the tail light. Another wire goes to the idiot light. My memory is fuzzy, but there probably is a ground and/or a battery lead coming out of the box as well.
I believe the circuit is measuring the current going to the tail light. If the current is too low (implying the bulb is burned out), then it connects the wire to the idiot light to ground or battery+. The circuit is falsely detecting low current.
Several things might fix this:
1) Change the bulb to one that draws more current.
2) Put a resistor in parallel with the tail light, to double the current.
3) Buy another "box" on ebay (I tried this, and it did not solve my problem).
I also have a related (?) problem with the low fuel light not working when it should. I tested the circuit to the low fuel sensor in the reserve tank, by grounding the wire, and Low fuel light works. I replaced the low fuel sensor, no change in problem.
I noticed, that if I take a several hour trip on the turnpike, the tail-light indicator will eventually go out and stay out. If that happens, and I run low on fuel, the "low fuel" indicator works again.
This has me thinking this could be a voltage problem. After a long high speed trip, the main voltage regulator normally reduces the voltage, to prevent over charging the battery.
I have wondered if the sensor circuit has a secondary voltage regulator (or a Zener Diode) in the idiot light cluster, which instead is providing full battery voltage to the sensor circuits. This would also explain why the "tail light" indicator turns off when I apply the brakes, since the overall voltage drops a little when the brake lights come on. The wiring diagram in my Honda repair manual does not go into that much detail, and I have not pursued this theory.
Posted on May 14, 2010
Hi and welcome to FixYa,
A most likely suspect would be a defective switch. Offhand:
Posted on Feb 22, 2009
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