Topic: Dyna coil install-- now no power to ignition switch, bike is dead

[judder]

Ok I just installed Dyna 3 ohm coils on my 1974 CB750, so before I started in on the electronic ignition I wanted to see if I got spark with the new coils. Well I don't have power to anything now. I cut the stock coils out and attached the blue and yellow (I believe those are the colors) wires to their respective coils and the black wires to the other side of the coils. Where did I go wrong? Do I have a problem totally unrelated to the coil install I wonder? The battery is charged and is in good working order. Thanks for your input.

Stumped

[scondon]

With the key turned to "on" position all of your lights, as well as your starter motor, should function regardless of what is going on with your coils. Coils only effect spark to the plugs, and not other systems. Revisit the work you did while installing the coils and look to see that you have reconnected the ground wires, and haven't yanked anything else loose. Check your fuses with a multimeter to see that their not blown.

[HondaMan]

Your keyswitch's plug is in that same area: could you have accidentally tugged it apart a little bit? They often don't contact each other very deeply inside their halves.

[judder]

ya I can't figure it out, I disconnected the ignition switch and plugged it back in again just to make sure. All of its contacts look clean. All wires under the tank look fine at least the parts of them that I can see. I made sure all of my connections are tight and metal on metal. It has got to be something stupid that I did, but what? I guess I will sleep on it tonight and head out to the garage in the morning with a meter and figure it out. The bike ran with the stock coils before I tried to "make it run better."

Thanks for you help.

Jud

[HondaMan]

Could it be the fuse? If it was marginally damaged before, the extra current of the 3-ohm coils could have made it breathe its last.

[judder]

I'm going into the garage now, I will check the fuse, I'm hoping it is that simple. Thanks for your help. Electricity to me is kind of like voodoo so I'm looking forward to learning something today.

Jud

[judder]

I checked the fuses on the bike and the lower fuse (20A) was blown so I replaced it with a new 20A fuse and it blew right away. My fuse box has a 5 Amp, 7 Amp and 20 Amp in that order going down. What is normal?

Thanks
Jud

[scondon]

Something in your wiring is not happy. Look for black, and solid color, wires. These are the ones that carry juice from the battery, and if they are worn and bare wire touches frame then your fuse will blow instantly.

I'm a big proponent of the "if it worked fine before I changed something, then I probably installed it wrong" method of troubleshooting. Look again at your coil wire connections and make absolutely certain you know which wires go to what and are plugged in correctly. You should have power coming in on Black or Black/white, and Blue-Yellow wires leading to ignition/points. Cross these and you'll blow fuses. Also, not sure about your model, but on mine there is a large green ground terminal that goes to frame on the coil mounts, did this go back in proper spot when you mounted coils?

[Spanner 1]

Does the fuse blow as soon as replaced or when ign. is turned 'on ' ? If when replaced, no ign., then must be a short to ground on the Red wire from the fuse to the ign. switch. BTW, that 20A should be a 15A fuse! Also, if blows when switched 'on' then both Red wire and all Black wires come into play. I would disconnect the power to the coils first ( should be black/white wire).......

[judder]

The fuse blows when I turn the ignition on. I bought some 15 amp fuses so I can sacrifice a few. I don't have the green ground on my coil mount. I connected the the yellow and blue wires to the correct coils. The black/white wires are attached to the coils on the opposite side from the yellow and blue wires. I used the coil mount screws to attach the the yellow, blue and black/white wires.

Now I've got to start playing with the wires to see where I went wrong. Thanks for all of your advice.

Jud

[HondaMan]

I checked the fuses on the bike and the lower fuse (20A) was blown so I replaced it with a new 20A fuse and it blew right away. My fuse box has a 5 Amp, 7 Amp and 20 Amp in that order going down. What is normal?

Thanks
Jud

That 20 amp should be a 15 amp, which will keep the wires from melting. The others are OK.

Try unplugging the BLACK wire in the headlight that goes to the RUN/STOP kill switch in the right handlebar, which returns from that switch as a BLACK/WHITE wire, and plug them straight together in the headlight. This will bypass that kill switch for the moment as a test. Then try turning on the keyswitch to see if the fuse holds. If not (i.e., fuse blows anyway), the wiring is shorting from BLACK to the frame, possibly, somewhere else. If that fixes it, the problem may be up inside the right handlebar switch. There are quite a few wires in that switch on the late model of 1974 (K4 late version), and they can sometimes break a tiny strand and touch the handlebars with it, making nasty shorts to ground (I've seen this several times). This jumper business I mention here will bypass all that to see if that is where the trouble might be. Make sure to plug it all back together properly or else the START button may not work afterward (it shares that BLACK wire inside the right handlebar's switch).

On some bikes with lots of miles, the (now hard) black pastic overjacketing on the wire harness has cracked: the edges are as sharp as a knife. I have seen this cut through the other wires at places like the steering head (where it moves a lot), causing shorts to the frame or to other circuits, making strange things happen. Take a look around for that: try moving the handlebars to a different position to see if it might make the short quit (then you've got a clue!).

[chickenman_26]

The black/white wires are attached to the coils on the opposite side from the yellow and blue wires. I used the coil mount screws to attach the the yellow, blue and black/white wires.

Now I've got to start playing with the wires to see where I went wrong. Thanks for all of your advice.

Jud

Without a picture, I'm not sure if I'm understanding you correctly. But it sure sounds as though you used the coil mounting screws to attach the blue, yellow, and black/white wires to the coil's laminated core, rather than its primary terminals. That explains the dead short of the black/white wire to ground that's popping your fuse. The wires should be installed to the coil's primary terminals as in the pic below, using the 10-32 x 5/16 pan-headed screws in the mounting hardware kit. Black/white and blue (or yellow) are attached on the same side of the coil - one at the top, and the other at the bottom. Dyna's dual output coils have no polarity, so either wire can be attached at either location.

Stu

[judder]

Looking at the image you posted, I wired the damn thing up wrong. Sometimes I don't see things that are right in front of my face. Once again I take an easy install and turn it into a killer of a a couple of days. Oh well at least I'm learning, I hope.

Thanks

Jud