Topic: electrical question--do I need diodes to make my indicator light work?

[jessezm]

Dudes, help a brother out:

I've redone the wiring on my cafe project, and added an aftermarket mini speedo with all the idiot lights incorporated.  Thing is, there is one light that flashes for the turn signals, whereas the original wiring had two (one for each directional).  So if i plug both of the turn signals into the indicator light on the speedo, won't they make all the signals flash at once?  I guess my question is, can I get some kind of diode that will take the signal from each turn signal and send it to the indicator light without feeding back to the other turn signal?  I just got home from the bar so this may not make sense....  I guess I'll know by the responses in the morning...

[DHolbrook]

I speak bar talk I guess too!

You are correct across the board, you'll need to install a diode on each turn signal wire before it reaches your indicator light.  I went to radio shack and bought a diode that had the lowest rated Peak Inverse Voltage.  I think the diode itself was 100 watts.  It was only $1.65 for two.  I went home and altered my connections like so:

I soldered a diode into each signal power feed.
I choose one of the two wires running to my dash light to be a power and the other to be a ground.
I ground the ground wire I choose for the idiot light.
I connected together the two power leads from the signal sides after they traveled through the diode, to the power lead to the dash light. Three wires all together.
Turned the key, hit the switch, and everything worked.  I had my headlight on so fast after that!

[TwoTired]

Kinda depends on how your new wiring matches a Honda diagram.

The early Hondas had only one indicator lamp.  No diodes.  Just connect each of the two leads of the bulb filament to each side of the turn signals.

Doesn't work with LEDs, though.  But, we haven't a clue how your "aftermarket mini speedo" is wired internally. (no info provided)
But then, you never told us what lamps you are using, or what your current wire diagram looks like either. 

So, maybe you need diodes, and maybe you don't. 

[jessezm]

Okay, okay, okay, more details!  Now that I'm fresh and all coffee'd up...

DHolbrook, I think that is exactly the info I needed, but just in case, here's what I can say about my setup:

'77 CB400f, control switches from K & S technologies, speedo and tach from cycle recycle, mini-stalk turn signals from K & S.

The Mini-Speedo is from cycle re-cycle, and I believe it is lit with LEDs, but it did not come with a wiring diagram.  I used my original diagram to figure out that the oil lamp and neutral lamp needed one wire to hot and are grounded to the leads from the neutral switch and oil switch.  The high beam indicator is wired to the high beam lead and to ground, and the backlight is wired to a hot and ground.  The turn signal indicator is the same--one wire to ground, and one to power.  At first I hooked it up to the gray wire from the flasher relay, but then it stays on all the time and blinks only with the signals.

So all that leads me to believe that I'm in need of the diode set up. 

[TwoTired]

I am not familiar with the products you mentioned and have no data for them.

LEDs only illuminate with power of one polarity.  If you have access to both ends of the illumination device, you can reverse polarity and see if it will light.  Lamp filaments don't care about polarity and will light with either polarity.  LEDs will only light one way.

If the instrument you have uses a common ground for all internal devices, putting positive on the ground terminal is not recommended as there may be other devices inside that may be harmed by such occurrence.  It's a hazard frequently encountered when you don't know what's inside the electrical box.

When on the frontier, it is easy to tell the pioneers from the indigenous population.  The pioneers are the ones with arrows in their backs.

[eurban]

I am pretty sure that I have the same speedo also available through drag specialties.  It uses LEDs for the idiot lights. I have LED turn signals (which will light up with minimal current) front and rear and when installed without diodes I did get cross illumination through the single idiot light.  Diodes fixed the problem.  I am not sure whether turn signals with conventional bulbs would have the same issue.  The diodes are inexpensive so its probably worth putting them in.

[jessezm]

Yep, that's the plan--I got two kinds cause I didn't know which ones to use.  first set are 12 volt zener diodes, and the second set are 3 amp epoxy rectifier diodes, 50 PIV.  Any idea which ones I should use?

[MJL]

I am pretty sure that I have the same speedo also available through drag specialties.  It uses LEDs for the idiot lights. I have LED turn signals (which will light up with minimal current) front and rear and when installed without diodes I did get cross illumination through the single idiot light.  Diodes fixed the problem.  I am not sure whether turn signals with conventional bulbs would have the same issue.  The diodes are inexpensive so its probably worth putting them in.

Both incandescent bulbs and leds have two leads. To make a single idiot light work, if it is a regular bulb you just connect one side of the light to the left blinker and the other side to the right blinker. They won't cross-illuminate.  To use an led you will need two diodes, one for each left and right, and connect them both to the same lead on the led. Ground the other. Like Twotired said, leds will only light one way.

[TwoTired]

Yep, that's the plan--I got two kinds cause I didn't know which ones to use.  first set are 12 volt zener diodes, and the second set are 3 amp epoxy rectifier diodes, 50 PIV.  Any idea which ones I should use?

A diode blocks current condition it one direction.  It does need a bias voltage for it to conduct in the forward direction.  Depending on the material used during construction, that voltage somewhere between 0.4 and 0.7 volts.    Rectifier diodes fall into this category.
Zener diodes are special construction that require a higher voltage to conduct, according to their rating.  Ie. a 12 volt zener won't conduct until 12 v of the correct polarity is present across its terminal.   Then it will conduct vigorously and unless the input current is limited, will often self destruct.

PIV is Peak Inverse voltage.  This is the voltage the device will withstand with the polarity in the reverse (non-conduction) direction.

You don't want Zeners in this application.  You want to use the rectifier diodes.

[jessezm]

Excellent, thanks for the info, just what I needed!

[jessezm]

And we have VICTORY!  I used the rectifier diodes, crimped, soldered, and heat shrinked.  I used a brass connector for the ends feeding the indicator light, and a silver connector for the ends coming from the blinker leads.  Then I used a 2-into-1 connection (not soldered) for the two brass ends to feed into the indicator light.  Works like a charm!

[DHolbrook]

Great work man!  Any pics of the speedo you are using?

[KeithB]

That's a nice clean job!
I have to go back a re-do mine now 

[jessezm]

Thanks!  Here's a few pics of the speedo: