Ignition Circuit Problem

[BlueNorth]

I have a 1979 SF that was running quite well until I parked it a few years ago. It was stored in a shed all that time.
The cylinders and top end of the engine are original SF. The bottom end from the connecting rods down is from an SG (1/4 miles of original engine). I kept the top end of the engine because I had just had the cylinders bored to first oversize (new pistons and rings) and had the valves lapped. Engine still has points ignition.

When I turn the key on, the check light is off, neutral light is on. Alternator passes slap test. When I put the front brakes on the rear brake light comes on. When I put rear brakes on, the brake light does not come on. No rear tail light. Signal lights work fine. Horn works fine.

From there it goes downhill as I have no rear tail light and no spark. Starter does not work.

I took the kill switch apart and found the internal components had broken due to age so I installed a new kill switch. It seems to work fine as the check light comes on when I turn the switch off and goes out when I turn the switch on.

I eliminated grounding issues as much as possible by routing every ground wire directly to the battery. The ground cable from the battery is still connected to the frame at the factory connection.

I replaced all of the original glass fuse holders with new blade fuse holders. I took apart every connection in the wiring harness and replaced connectors that appeared to be corroded. I cleaned the rest with contact cleaner and sandpaper.

I've spent three hours a day for the last two weeks trying to isolate the problem but I'm getting nowhere and extremely frustrated.

The bike is on the center stand but to my knowledge there isn't a kill switch on the stand - is there?

If I connect power directly to the brake and running elements in the tail light, they work fine. Battery is new last week and fully charged.

Any ideas?


Wayne

 

[weaselbeak]

Cross the solenoid with the switch on. If it cranks and runs you have only a starter wiring glitch to chase. If it will not run, you have an ignition problem to chase down. You can jump a hotwire to the common leads on your coils to bypass all ignition wiring. You need to have voltage to the coils with the switch on. Same with the starter button, kill switch, etc. Some bikes won't crank without pulling in the clutch lever. Rule stuff out one piece at a time.

 

[5twins]

You may need to disassemble and clean the ignition switch. The tail light should come on when you turn the key on. It's wired directly to it. If power for that isn't getting through the switch, there's a good chance power for other things, like the ignition, isn't either.

The switch only has 3 wires according to the wiring diagram for your model so should be easy to test. Red is power in from the main fuse and battery. Brown is power out back to the other fuses. L/Y (blue/yellow) is power our to the light checker which sends it to the tail light.

If the switch checks out OK, my guess is you screwed up the wiring on the new fuses.

 

[BlueNorth]

I have 12.58 volts to the brown wire. I'll check the L/Y for voltage.

The problem existed before I replaced the fuse holders. Fuse holder wiring is simple enough since I'm inserting the fuse holder in series on the same color wire.

I should add that the PO had installed individual glass fuse holders instead of the fuse box. He also had a wire tapped into the brown wire that went to the rear tail light assembly but I don't recall which wire it was connected to. It might have been for the license plate light. It definitely wasn't part of the original harness.

The kill switch/starter assembly is hanging off the handlebars at the moment as I'm trying to establish power to the tail light and the ignition circuit. I know that the assembly must be on the handlebars for the starter button to work. If I'm kick starting the bike I should be able to rule out starter circuit problem for now since that would require the starter relay to switch on. If the starter relay was somehow engaged without the starter kicking in, that would turn the tail light off but the ignition circuit would still have power, wouldn't it?

I had the ignition switch out of the bike and took it apart as far as removing the plastic cam so that I could see the contacts. They looked quite good. I cleaned them with a file and contact cleaner and put the ignition switch back together.

Should I disassemble the ignition switch further?

Thanks for the input. I really appreciate it.


Wayne

 

[5twins]

You shouldn't need to take the ignition switch apart again, or any further than you did the first time. But I would give it this simple test - check for continuity between the red wire and the brown in the "On" position. Also check between the red and L/Y. Red and L/Y should be connected in the "Park" position as well. If that all tests out OK, I'd move on to the fuses. The brown feeds power back to them from the key switch. Shortly before it reaches them, it splits into 3 wires. The brown continues on but a R/W branches off for the ignition and a R/Y for the lights .....

The R/W runs up through the kill switch and then to the coils. It is split in 2 there, one R/W for each coil. Test them there to see if you have power to the coils.

 

[BlueNorth]

I really appreciate all of the suggestions. Knowing which area to concentrate on is usually half the battle.

I took a closer look at the wiring harness, starting at the three wire plug that connects to the ignition key switch. I discovered an area on the brown and blue/yellow wires that had rubbed bare. You can't see it without twisting the wires but it was there.

The blue/yellow wire had no conductivity for approximately three feet between the key switch and the battery area on the bike. It also appears that the wiring insulation on the blue/yellow wire close to the key switch connector had melted at some point. I replaced the entire blue/yellow wire and repaired the brown wire.

I then had conductivity on the blue/yellow wire as far as the light checker. I couldn't find positive voltage on any wire (connected to the light checker) other than the brown wire. I'm guessing the blue wire from the light checker should be the positive voltage to the rear tail light but there is no positive voltage on that wire. The blue wire also has the appearance of melted wire insulation on the female side of the tail light connector. It all seems to point towards something shorting out at some point before I owned the bike.

There is no license plate light on the bike so I reasoned the PO had run the positive voltage tap from the brown wire to the blue wire on the rear tail light. It had been connected at the rear tail light at one time but I had neglected to label that single wire when I had taken the rear fender off (long story that I won't go into now).

When I plugged the PO's tap from the brown wire into the blue rear tail light wire, everything seemed to act normally. Rear tail light is on with the ignition switch and the light checker light is off on the instrument panel.

I discovered a ground wire on the rectifier that I had neglected to connect when I decided to run all grounds to the negative battery terminal. The wire wasn't connected to ground at all. That was 10:30 last night so I still have to make that repair.

It appears something is not working on the light checker that the PO knew about. The bike was running when I parked it, with the brown wire tap in place. Is it potentially harmful to leave this bypass in place?

I'll let you know how things progress from here. Again, thank you all for your kind considerate help.


Wayne