Topic: LED Turn Signals and Instrument Light (‘74 CB750)

[Yoshimitsuu]

Quick question about converting to LED lights (at this point I’ve done the headlight, Instrument lights, tail light and turn signal lights). Since I switched over to LED and bought an electronic flasher relay, the Turn light in the instrument cluster won’t light up. I did some digging and found that some people reporting having to attach diodes to get this setup to work but I’m not sure if that’s what I have to do in this situation. Thoughts?

I also found this picture which looks pretty foolproof (shoutout to the user who drew this up, thanks in advance!). Is this what I should be following?

[Deltarider]

For those that must have leds, consider this to address the somewhat 'dead' appearance that a led indicator (or brakelight!) inevitably brings: https://www.louis-moto.co.uk/artikel/led-turn-signal-with-sequential-effect/10035508?regionPopupClicked=true&_ga=2.57432236.721500908.1511613631-351993761.1511173123 And E-approved.

[Bodi]

The drawing is for using a single idiot light for the signals rather than two, it will work for a single LED if you get the polarity right.
For models with the single idiot light Honda used a different (cheaper) scheme with no diodes. A small instrument bulb for the idiot light is wired between the flasher bulb "hot" wires, when one side is powered the small bulb lights with its power going to ground through rhe other side's bulbs. That can not work with a LED idiot light as-is, it needs to be rewired like your drawing. As long as you use an automotive drop-in LED replacement instrument bulb you're ok. If you use bare LED you need a series resistor to limit current - a bare LED connected to 12V will be very very bright.... for a few milliseconds as it burns out.

[Yoshimitsuu]

Okay, awesome. I ordered a cheap diode kit to see if I could make it work. With the new LEDs and the new flasher relay the lights are more consistent which I like. It’s just getting the light in the instrument cluster to work along with it. Hopefully that diode kit gets it to work. Thanks again guys!

[KeithB]

Did you try reversing the wiring to the instrument LED?
They are "one way" devices.

[rotortiller]

[Duke McDukiedook]

Eh, I bypassed all this hooey by just using regular incandescent bulbs for the rear signal along with a new flasher relay. No need for diodes at all and the rears only light up when I use the signal so most of the wattage is saved by using LEDs on the front stalks.
 

[Bodi]

Good plan. Often people install complete LED signal units though so the original tungsten bulbs are not an option. Bikes with dual signal indicators (kinda pointless I think as once you look down and see a flashing light saying you forgot to cancel the signal a few miles back you don't really care which way you're not turning soon) don't need these diodes regardless.

[rotortiller]

What you may find with the old school "hooey" tiny single dash indicator system is that the electrical current reverses direction during left to right selection in the tiny dash indicator bulb picking up a ground through turn signal bulbs element to ground. Because the small ma current drawof dash light is so tiny it won't light the incandescent signal bulbs however insert a low current LEDs and it may well light up what you expect to be inactive.   http://www.oregonmotorcycleparts.com/Diagrams/CB750k2.jpg

[Bankerdanny]

Just use conventional bulbs in the rear signals and you should be fine. Since they only light up when the signals are on there is no savings using them in the back.

I also tried LED at all 4 corners, and even with a solid state flasher they still didn't work right. Put the regular bulbs back in the rear signals and they worked perfectly.

[KeithB]

First, using LED to "save power" on the turn signals is rather pointless considering how long they are actually loading the charging system.
That said, I have used LED signals all the way around, with an LED dash light (with diodes) and a cheap "solid state " speed adjustable flasher and they worked just fine.

[rotortiller]

Yup, sometimes the LED signals are a better, easier and cheaper alternative so it is wise to know why diodes are needed or how to install. Pretty easy to make a small adapter harness with diodes so the OEM wires do not have to be cut.