No spark when using ignition switch

[Max V]

Hello,

I have a 1977 cb750a that has no spark when I use the igniton switch. If I use a jumper wire between terminals on plug for ignition switch, starts right up. Took apart switch, everything looked good, nothing burned or melted. I get continuity on the switch between bat and ignition and between T1 and T2. The dash lights come on when switch is in ON position and tailight comes on when P position. Is this an ignition switch problem?

Thank you

 

[brettp]

If you have to manually make a connection at the ignition switch (key) to make the bike run, I'd say you narrowed the problem down perfectly fine.
Just recently I lost a connection at my ignition. Turn the key... no headlight, no oil light, no neutral light, no lamps. I knew all those things were 'connected' at the ignition switch so I didn't bother looking any further. I stuffed some rags under the ignition switch and blasted some electronics cleaner into the switch. All kinds of black crap came running out of there. Did that until the nastiness was all but gone. Let it dry for a couple minutes and bike powered right up.

 

[Max V]

Thank you for the reply. I completely disassembled the switch and it was in great shape. That is why I find this confusing.

Thank you again

 

[brettp]

Thank you for the reply. I completely disassembled the switch and it was in great shape. That is why I find this confusing.

Thank you again

Don't forget to check continuity between wire ends as well as across connectors. We have all had connectors corrode today needed some wire brushing or sandpaper to reestablish the connection

 

[Max V]

Don't forget to check continuity between wire ends as well as across connectors. We have all had connectors corrode today needed some wire brushing or sandpaper to reestablish the connection

Thanks for the suggest. The previous owner lit the harness on fire rebuilding the carbs. A couple months ago i rebuilt the entire harness put in new connectors and plastic plugs. Everything worked great until this. Very perplexing. I ordered a new switch- it is the only logical solution. I'm going to try a couple tricks tonight and see if the issue gets resolved. I don't want to keep hot wiring off the plug

Thanks again for the suggestions

 

[brettp]

Let us know how it goes

 

[Max V]

Let us know how it goes

I have a new switch that is supposed to arrive on Monday. I will let you know what happens. Since i have continuity on the terminals with the switch turned on, I wonder if there is too much resistance 13ohm on all channels. I will test the ohms on the new switch before I install. Thank you for your suggestions.

Have a great weekend.

 

[brettp]

13 ohms between terminals of the switch?

 

[Max V]

13 ohms between terminals of the switch?

Yes. A new switch arrived yesterday, no change. I need to pull the tank and go through the wiring again. I have aftermarket Dyna coils and there might be a wiring issue with the coils.

 

[brettp]

Your kill switch is in the run position?

 

[CBJeebie]

Bad crimping at connectors???

 

[Max V]

Your kill switch is in the run position?

Yes, Im a little smarter than that.

 

[brettp]

Yes, Im a little smarter than that.

Had to ask, man.

 

[brettp]

You said it will fire if you jump two terminals on the ignition switch. Which terminals are those?

 

[Max V]

battery,ignition TL1 and TL2. I fixed the issue. It must have been a poor connection in the wiring harness, I just checked all the connections and it starts with the ignition switch. My confusion comes from the fact that I could always start with the hot wire, but not the ignition switch. Maybe a resistance issue? Thank you for your help.

 

[brettp]

Well, I was out of ideas so I'm glad you're fixed! Could be high resistance due to corrosion somewhere. If it comes back, you need to trace all ignition wires to their connections.

 

[Max V]

Thank you. I traced all the wires and couldn't find any issues. Just glad it has been resolved.

Thank you for your help