1983 vt500 shadow. I connected the battery backwards and now the dash lights wont light up

SOURCE: VT500 Cooling fan blowing fuse

from what you are describing the fan is drawing too much power, check to make sure there is nothing else connected to the circuit,

SOURCE: tail light indicator remains on, 1984 honda shadow

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.

SOURCE: 2004 Honda VT750 Shadow, no power. Just installed

could be a CDI unit.

SOURCE: 2007 Honda Shadow Aero blows dash,warning light,

try changing the voltage regulator as its running out of controle the charger is over charging and you will boile the battery as well, its all down to the voltage regulator not doing its job right,,,easy fix? buy a new one but get the heavy duty reg and put some heat sink creem on the back of it so the heat can soke away into the frame fast that way they live longer
good luck mike.t

SOURCE: honda silverwing 600 scooter wont start flipped

worth checking the sidestand cutout switch as they're a known issue with many bikes