Author Topic: 76 CB750 turn signal issues (Read 2619 times)

cshanek · « **on:** April 15, 2020, 01:38:43 PM »

Greetings SOHC owners,

I hope all is well. Like a lot of you I have had some downtime recently to work on my bikes. I went through a series of interesting electrical issues with my 750 last year that included a faulty ignition switch and incorrect instructions from my harness manufacturer that essentially required a few oddball steps (concerning the headlamp and ignition) to get everything working.

I recently bought the 7" halogen conversion kit from CB750 (https://www.vintagecb750.com/search/?q=halogen - Part #: 09-0051 ) to install prior to running a couple of last tests and sealing everything up. Below is the current behavior I am seeing:

Left front turn signal is acting strange ...

* When both sets (R and L pairs) plugged in:
- L = Both front blink, back left blinks, brake light blinks (quickly)
- R = Brake light, right front and right rear blink (quickly)

* When Left set is unplugged:
- Right blinkers blink normally (speed), and brake light blinks too

* I tried an old left signal in place of the right blinker assembly and it behaved the same way

* Headlamp, brake light, starter all work (starter/ignition only works when headlamps is plugged in)

* When headlamp is plugged in and on normal mode:
Blinkers do not work at all (can hear them trying)
Rear light not on

* When headlamp is plugged in and on high beam:
Right front blinker solid
Rear light on

So from this I can assume it is not a short in the turn signal itself. The behavior that occurs when I plug in the left front turn signal is a little confusing to me though. I do not understand why plugging them in would make the right signals not work.

So on to the questions:

Any sage/salty advice?
Should I test the headlamp switch? It is a newish replacement from Vintage CB750
If so what is the best way to do this?
Is it safe to assume I have a short somewhere

bryanj · « **Reply #1 on:** April 15, 2020, 01:52:07 PM »

You have a bad ground contact somewhere

cshanek · « **Reply #2 on:** April 15, 2020, 05:18:54 PM »

Can I assume it would probably be wisest to start with testing the headlamp and right turn signal clusters/colors?

HondaMan · « **Reply #3 on:** April 15, 2020, 05:29:10 PM »

Often the ground wires from the turn signals are now rusty and corroded - or broken off entirely - in the lens, at the socket. The latter makes the "ground" circuit happen thru the filament of the bulb(s), so the flasher does not see enough current then to make it blink. It is a bimetal contact flasher, and it has to have 3 amps passing thru it to make it hot enough to curl and break for a flash OFF to occur.

Another thing that can cause it is poor contact between the steering bearings and the triple tree: the fork ears that ground the bulbs may not have a Green ground wire to them inside the headlight, especially if the Green wire(s) broke off the special nut inside the headlight where those turn signal stalks enter the headlight bucket. That nut has (had?) at least one tab or socket or ring terminal on it to ground the Green wire to the turn signal stalks.

cshanek · « **Reply #4 on:** April 15, 2020, 05:32:16 PM »

I have read that before I think, and completely swapped out the left signal, which seems to be part of the problem. The other (old) signal behaved identically. I should also mention that the front signals are new, which I know doesn't guarantee anything.

cshanek · « **Reply #5 on:** April 15, 2020, 05:34:35 PM »

I could test that easy enough with my multimeter and the bulb out though.

cshanek · « **Reply #6 on:** April 15, 2020, 05:37:52 PM »

I will check out the steering bearings/triple tree/fork ears option.

BenelliSEI · « **Reply #7 on:** April 15, 2020, 05:50:34 PM »

If you clamp an automotive jumper cable to the battery ground lug and then clamp it directly to each turn signal, while turning each one on-offf, you might quickly find the culprit.

cshanek · « **Reply #8 on:** April 16, 2020, 07:25:13 AM »

Is my assumption that it is not either turn signal, or at least the left turn signal since I swapped it out bad? What I should clamp the other end of the jumper to?

BenelliSEI · « **Reply #9 on:** April 16, 2020, 10:40:45 AM »

All I’m suggesting is that using the ground cable, you may be able to discover which part of your system is poorly grounded. For example..... if you clamp it to the stalk for the LF turn signal and it start working correctly, investigate more fully. CAUTION: some of the turn signal bodies have a small ground strap that connects the lamp socket (mounted in a rubber isolator) to the reflector and main bowl. If that is broken, the ground will not connect from the outside....... pull the lenses and check them first.

cshanek · « **Reply #10 on:** April 16, 2020, 10:52:40 AM »

Roger, will give this a go.

cshanek · « **Reply #11 on:** April 16, 2020, 11:37:07 AM »

I had just originally assumed that the orange/orange white in the left signal stock were somehow making contact with ground, but then got past that when I tried an older signal with the grounding straps you mentioned. I never though about the ground itself causing issues.

BenelliSEI · « **Reply #12 on:** April 16, 2020, 11:47:13 AM »

The other quick check is using a test light. Clip it to the (+) terminal on your battery. Now touch the prob to the (-) terminal. If it lights up, you have continuity and it works. Next touch around the bike. Handlebars, rear fender, lamp housings, engine case, turn signal housings and fork ears. Any metal part on the bike should give you a light. If it doesn’t, that portion of the machine isn’t grounded, and nothing mounted there will work...... Good Luck!

cshanek · « **Reply #13 on:** April 16, 2020, 02:05:40 PM »

Sweet, thanks ... adding it to the list. Snowing right now and a little cold in the garage but I should be able to get out in the next couple of days for next round of testing.

Keith · « **Reply #14 on:** April 18, 2020, 11:05:41 AM »

I have noticed that the "adapter" between the grab rail and the rear signals can be a problem...the ground can be lost there. I purchased two with no ground connection at all, the wires were installed after painting.

BenelliSEI · « **Reply #15 on:** April 18, 2020, 02:09:04 PM »

Keith...... I’ve had a few sets of those too! So well powder coated the ground river and wire never make contact. No amount of banging on the rivet would make the ground. Had to drill them out, scrape and re do the rivets. Weird!

cshanek · « **Reply #16 on:** April 25, 2020, 06:57:27 PM »

Well, I was able to get to pretty remarkable information from testing tonight.

The continuity testing via test light went just fine. All of the turn signal stalks lit up, as did the ground connections in the headlamp bucket, and pretty much everywhere else on the bike. The taillight assemble on the rear fender was a little sketchy, but there is a ground (green) wire coming from it that works just fine.I was a little surprised the frame itself was not grounded but I suppose that makes sense.
While doing the above I learned of something just freaking ridiculous. My store bought alligator clamp extenders were both garbage. The teeth of the clamp themselves were not making contact with the wire through the sheath. I cannot even guess how many times that screwed me up in the past while working on this bike. I think I always just assumed they were both good. I chopped them up and re-terminated them and all is well. Good lesson there.
Now on to the fun stuff ... I was able to get all of the signals to work if and only if I disconnected the orange/white from the right signal and the blue white from the left, leaving both connectors open. Oddly enough doing that makes everything work as expected (from a turn signal standpoint). Even the blinker/winker was operating at a normal cadence. The 2 front turn signals are after market with orange/orange-white and blue/blue-white connectors, and nothing indicating the grounding connection near the bulb (like in the OEM setup). I am guessing the bulb itself is grounded internally to the stalk though. Why would unplugging these make everything work?
Lastly I plugged in my Halogen conversion headlamp (from Vintage CB750, and got the same results. It comes on but seems to drain enough power so that the turn signals will not blink. When I flip the switch to high-beam, the signals are solid. I was looking at the bulb and noticed that it said "H4 12v 60/55w" in the assembly. The vintage CB750 people said in a email that I should be able to plug that guy right in without problems. Is the wattage of that headlamp too high? I see 12v 50/40 watt in my shop manual.

As always thanks to all the salty vets for helping an FNG through all of this.

cshanek · « **Reply #17 on:** April 27, 2020, 08:21:29 AM »

It's weird, it looks like most aftermarket bulbs are either 12v 50/60w or 12v 55/60w, though my shop manual says 12v 40/50w. So perhaps the headlamp I currently have should work.

newday777 · « **Reply #18 on:** April 27, 2020, 09:24:55 AM »

The original headlight was a sealed beam 40/50 watt. The halogen h4 was added sometime after your bike was originally sold. I was a parts manager in 76 and 77. I kept five h4 headlights in stock as an upgrade to see better.
If you are not running the bike leave the headlight off or the battery will drain fast. Keep the battery on a tender while testing so you have full power. Turn signals, especially with incandescent bulbs and a thermal flasher, as stock had, require full battery power to flash properly. How many volts on the voltmeter are you getting? How old is the battery?
Is the turn flasher relay still the old thermal type or have you replaced it with a new electronic flasher(takes less draw to flash than thermal, I highly recommend you change to an electronic flasher)

cshanek · « **Reply #19 on:** April 27, 2020, 11:15:07 AM »

The battery is probably a couple of years old. I have had it on a tender on and off over the last month and I *think* the battery was fully charged when I tried the headlamp last time out. I will head out during lunch to test the output of the battery and to take a look at what flasher I am using.

cshanek · « **Reply #20 on:** April 27, 2020, 11:18:14 AM »

The battery is putting out 12.48v. The flasher relay is Mitusba FR-2204 I think (a number is rubbed off). https://www.cmsnl.com/honda-ca125-rebel-1996-t-portugalkph_model1342/relay-comp-winker_38301kg0024/#.XqchxJl7mHs.

cshanek · « **Reply #21 on:** April 27, 2020, 12:14:54 PM »

I should also mention that to get the ignition switch to work at all (I think due to 1976 headlight safety change), we had to run a jumper from the solid blue headlight group to the green/red group from one of the 2 handlebar switches.

cshanek · « **Reply #22 on:** May 03, 2020, 09:15:45 PM »

I did some testing tonight. A multimeter testing the battery yields 12.3v. When I test the hot line in the headlamp to a ground I get 11.3v. Is it normal to be running low in the headlamp bucket? If so why? Pretty much every hot line up that is either 11.3v or 10.5v. I also tried an older normal headlight and got the same result (turn signals stop working).

bryanj · « **Reply #23 on:** May 04, 2020, 01:10:03 AM »

Not sure what you mean, was the headlamp on with engine not running?

cshanek · « **Reply #24 on:** May 04, 2020, 07:07:14 AM »

Yes, engine off, battery reads 12.3v, the blue line in the headlamp connector to ground reads 11.3ish. Back to the battery yields 12.3v. Just noticed a 1+v difference between what the battery was putting out and what was available in the hot lines in the headlamp rats nest.

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Author Topic: 76 CB750 turn signal issues (Read 2619 times)