Topic: Wiring 1977 CB750 from scratch... Help?

[finches]

Hi everyone,

So I've been working on a CB750 K7. The stock wiring harness was shot (all plugs corroded away and wet), and basically none of the electronics were working when I got it (just the headlight).

I decided to re-wire the bike from scratch, but I'm a newbie at this and could use some help... I am using the following parts for this...

- DOHC Regulator/Rectifier
- Pamco Electronic Ignition
- New coils
- Motogadget m-Unit

I've wired up the m-Unit, coils, and Pamco ignition, but I'm not getting any spark. The m-Unit does light up, so I know its getting power. The bottom two lights on it are lit up (LOCK and AUX).

When I first turned the key, the ignition coils made a bit of a whine noise, then went silent... not sure if thats normal or not? I have tested the coils with a multimeter and they check out fine.

I've attached a diagram of where I'm at so far with the wiring. Is the ignition system wiring correct so far?

Next, I'll attach a diagram of the regulator/rectifier/alternator wiring, as I have some questions about that, too.

I'm new at this, so I really appreciate any help! Thanks!

[finches]

Thanks for the help, cal.

Ok... Here are the directions regarding the PAMCO unit...

1. Connect the red wires from both cables of the PAMCO  by extension to the Black / white wire from the kill switch that is connected to each coil. Alternatively, you could connect the red wires to another source of switched battery, such as the rear brake light switch or regulator to avoid having to remove the gas tank.

2. The black wire from both cables of the PAMCO is connected to the frame.

3. The green wire from one of the cables is connected to the 1 - 4 coil. (blue wire) located in the vicinity of the rear brake light switch connections.

4. The green wire from the other cable is connected to the 2 - 3 coil (yellow wire) located in the vicinity of the rear brake light switch connections.

Do you think those directions correspond correctly to my diagram? Is what I have shown in my diagram the only things I need in order to get spark?

Thanks!

[finches]

So if red Pamco wire to black coil wire to AUX isnt correct, can you tell me the right way to wire it? Im confused.

Probably being dense here but theres something about it that Im not getting unfortunately.

[madmtnmotors]

On your diagram, you are tying the coils to ground? From AUX, go to coil BLK. The wires from the Pamco to the coil are the "grounds". Doesn't the Pamco need a power source to it also? If so, use a tap from AUX.

I think it's a poorly drawn schematic. The schematic appears to be connecting everything to ground, but what I believe is really intended to be shown is that the grey wire from the Pamco contains the Black/Green/Red which then "splay out" at what appears to be a "connection". What he is trying to show in the schematic is:
>Red connects to Aux and coil Black
>Green connects to coil
>Black wire from Pamco to ground

A proper schematic would show the Red, Green, and Black wires drawn all the way back to the Pamco unit. Showing them joined into a common "sheath" implies a connection (as though all three wires connect together at this point).

[finches]

Yes! Thats right... Its just drawn poorly.  Thanks for clearing that up.

[madmtnmotors]

Happy to help. After your response to Cal I had to go back and look at the schematic more closely, since I had interpreted too many connections as well. The Dyna ignition is similar in that all the wires share a common (grey) sheath, so once I figured out the "grey" wire the rest became more clear. 

If Cal can't figure it out then no one can! 

[finches]

I've updated the diagram so its not as confusing... Is this the proper way to have it all wired up?

Thanks!

[finches]

Thanks, cal. I can't thank you enough.

I'm still just not getting any spark though. I rechecked each coil and the resistance is where it should be... so I'm guessing those are good. Maybe it's a problem with the way I installed the PAMCO unit where the old points went. I'll try it again tonight and report back!

[madmtnmotors]

If you have the LOCK and AUX both solid lit, then you're passing 12v to the coils. Now, you need the Pamco to send the trigger over their grey  green wires to the coils to spark the plugs. How are you testing the "spark"?

I hate to say it, but it is possible that you damaged the Pamco if you truly had it wired as diagrammed with the RED wires tied to ground. By the way, what coils are you using, and what plug wires/caps? Lastly, the m-unit needs to be tied to a solid ground as well. Even for testing purposes.

FTFY 

The grey wire in the original diagram was just the outer sheath of the red/green/black three-wire bundle.

Check for voltage out from the m-unit (orange?) to make sure you have voltage feeding the coils (black) and the Pamco (red) instead of just relying on the m-unit lights.

[finches]

If you have the LOCK and AUX both solid lit, then you're passing 12v to the coils. Now, you need the Pamco to send the trigger over their grey wires to the coils to spark the plugs. How are you testing the "spark"?

I hate to say it, but it is possible that you damaged the Pamco if you truly had it wired as diagrammed with the RED wires tied to ground. By the way, what coils are you using, and what plug wires/caps? Lastly, the m-unit needs to be tied to a solid ground as well. Even for testing purposes.

Ok Cal, I'll address your questions here...

1. I was checking for spark by putting a plug onto bare metal on the engine and cranking it with the kick starter.

2. I am using the coils that came with the Pamco kit... They are part #17-6823 at VintageCB750... http://www.vintagecb750.com/parts/480/17-6823.jpg

The caps came with the kit, as well. They are the NGK ones.

I should note that I also tried the original coils and didnt get any spark. And I also tried switching the coils around.

3. Also, madmtnmotors is right, I never had it wired any differently than in the final diagram I posted... The first diagram was just drawn poorly - as the gray "wire" was just a sheath that housed all three wires from the Pamco. I redid the schematic to reflect the Pamco wires properly, but they were always hooked up the same as they are now.

4. Yes sir... The m-Unit has a secure ground and also lights up properly... LOCK and AUX are lit up solid.

---

I guess it's looking like a problem with the PAMCO ignition unit... I'm going to do the test that madmtnmotors suggested and see what I get. Thanks for the suggestion, madmtnmotors.

Thanks

[finches]

I have what is shown in the diagram + turn signals and headlight so far.

[madmtnmotors]

whether you have power at the end of that wire (coil end) is worth investigating.

+1. Have you verified voltage at the power connection to the coil?

[finches]

Little update here... So here is where I'm at with the regulator/alternator wiring so far.

I have 3 wires that I'm not sure about (marked in the attached schematic with question marks).

1. I think the two coming from the alternator plug go to neutral and oil pressure switches... Are these necessary?

2. Where should I connect the black wire from the regulator to? I've seen diagrams that show it connected to the key switch... should I do this somehow? Or can I plug it into the m-Unit somehow? Or?

3. Does everything in this schematic look correct?

Thanks in advance. You've been a GREAT help so far.

[finches]

whether you have power at the end of that wire (coil end) is worth investigating.

+1. Have you verified voltage at the power connection to the coil?

I just went out and checked... It has a little over 12V at the coil connections.

[madmtnmotors]

whether you have power at the end of that wire (coil end) is worth investigating.

+1. Have you verified voltage at the power connection to the coil?

I just went out and checked... It has a little over 12V at the coil connections.

That's good. Troubleshooting electrical often involves figuring out what it's not. 

I haven't checked, but maybe Pamco's site has troubleshooting procedure's for their ignition?

[scottly]

The extra "alternator" wires are for the nuetral switch and the oil pressure switch. On a normal wiring system, the black regulator wire would be connected to the ignition switch, but I'm guessing with the M-unit it would be connected to the Aux, just like the coils? Not sure how the M-unit handles a handlebar mounted emergency kill switch? Cal?

[finches]

The extra "alternator" wires are for the nuetral switch and the oil pressure switch. On a normal wiring system, the black regulator wire would be connected to the ignition switch, but I'm guessing with the M-unit it would be connected to the Aux, just like the coils? Not sure how the M-unit handles a handlebar mounted emergency kill switch? Cal?

So I can just leave the neutral switch wire and oil pressure switch wire unplugged in the harness? My gauge doesnt have neutral or oil lights on it.

[finches]

I have spark now! The one coil had a terminal that was touching the nut from the bracket that holds the coils on the frame... Once I fixed that, I was getting nice blue spark out of both coils! 

Thanks guys! Onwards to finalizing the rest of the wiring...

[scottly]

Handlebar KILL switches are easily managed with a momentary. Wire it to the START input. START output takes switched power to the solenoid (if present). Press the momentary once, you get a "start" signal. With the motor running, a double tap "kills" the motor, but not the switched power.

Ahh, you press the start button twice to kill the motor. Sounds like the "m" stands for Microsoft.

[finches]

Hi,

Does anyone know how to wire in the stock right side controls to the m Unit? I'm looking to have the stock switch work to power my electric start...

There are 5 wires in the plug from the right-side controls... Two blacks, black/white, black/red, yellow/red.

There are 2 wires from the solenoid... Yellow/red, green/red.

I'm guessing the yellow/red from the starter switch goes to the m-Unit's Start input, and the yellow/red from the solenoid goes to the Start output, or?

Also, what other wires need hooked up to the m-Unit just to get electric start functionality?

Thanks!

[finches]

The black wires on your RH switch operate the KILL by bringing power to KILL, jumpers to BLK/WHT when moved to RUN. If you want to maintain that functionality, then do the following:

AUX - Black wire to KILL, BLK/WHT from RUN to coils.
Look at START button on RH. The Y/R from START needs to be a "ground" at the bars, then run to m-unit START input, output to solenoid (now it's switched power). You then need to take the G/R at the solenoid and secure to chassis ground.

The BLK/RED I believe is headlight power on the electric start interrupt (someone confirm that please?).

The extra black on your stock controls should go to ground. This sounds odd, but you need to understand, the stock controls and harness function in reverse to how the m-unit does. The m-unit is only looking for "ground signals" coming into the left side. The stock harness sends power (via BLK, Br/WHT) through the controls, then onto the components. So you need to eliminate power at the switch controls (except as described above for KILL/RUN if you want the stock functionality) and make sure everything is essentially behaving as a ground.

Make sense?

Ok... So I wired the Y/R from the START button on the RH control to the m-Unit START input... And I made the black wire coming from the START button into a ground, but I'm not getting anything out of the start button, so I must have something set up incorrectly.

What makes the ground complete when I push the START button so that the m-Unit turns on the starter motor? I noticed that when I just hold a wire straight onto ground from the m-Unit START input, the starter motor does kick on... so it works fine... I'm just wiring something wrong from the RH control.

You mentioned making the Y/R from the START button a ground at the bars... I dont really understand what this means since that wire just runs straight into the Start button, and the other end of it goes to the m-Unit...

Thanks!

[finches]

Hi Cal,

Thanks for the help. I guess the start button is faulty... I took apart the casing over the RH control and looked at the Start button... Three wires into it. Black, Black/Red, Yellow/Red... I've tried different combinations of grounds and m-unit inputs with no success.

[finches]

Ok guys,

Just a couple more things to clear up and then I'm good to go.

I've attached the most recent wiring diagram for the bike. The electric start is working, I have spark, the lights all work.

1. I'm using the stock RH controls. I can just use the m-Unit's KILL feature with the wiring the way I have it now? By double tapping the START button on the RH control it will kill the engine?I want it set up that way so I dont need to mess around with wiring stuff from the RH control to the coils, etc. I'd rather just use the one button to both start and kill the engine.

2. Can I put the main 30A fuse on a regulator wire, or does it need to be on the m-Unit red wire? I ask because I already have fuse holders for 16 awg wire, but I dont have one for the thicker gauge red wire that the m-Unit came with.

3. Does everything look correct? Is there a better way to wire anything up than what I have shown in the schematic?

I have my turn signals/headlight/tail light all wired up and they are working great, but I omitted them from the schematic for now so that it's more simple and easy to understand.

Thanks everyone. I'm like 95% of the way there now.