Electrical problems, arrrgh!

[pasteurized]

Finally got my '750 basically dialed in as far as jetting with the V&H 4-1 and stock airbox yesterday, and went for a long ride (which was such an awesome reward). Fast forward to last night. Hanging out with some friends, and one suggests I try a bigger (louder) horn that he had on his FZR 600 at one point. Same terminal connections, easy swap. Beep beep, yep, louder! Figured I would switch back to the original and take the louder one home so I could correctly mount it at some point. Turn the key in the ignition to start her up and leave, and nothing. No lights at all. After some careful investigation, I found that I could start/run it by kickstarting (running off the stator, apparently), and found that a fuse was blown that apparently ran to the battery. Shut bike off as it was late and got a ride home. Got the replacement fuses this morning, popped one in, got lights back on the cluster. Set choke, hit start button, and it will turn over as long as you hold the button but will never fire or start. Tried kickstarting a bunch of times too, nothing. Checked battery cables, other fuses in the area, etc, but all looked fine. Being that everything was great yesterday (carbs freshly cleaned, ran like a bat out of hell, etc), I'm thinking that it probably isn't getting spark due to an electrical problem. I need to go over to his place (where the bike is currently stranded) and pull a plug and see if it isn't firing, which is what I expect. But my question is, what died, seeing that it started up last night without any battery connected at all? I went over and tried to start multiple times today in case it was flooded, etc, but it didn't. Also pulled the new fuse and tried to start it off the charging system like it did last night with the kickstart, no go. I will check the plugs (coils) for spark, but what gives??

[Steve]

Check your fuses. Here is a cut-and-paste from one of my previous responses concerning fuses:

The top fuse feeds the ignition key, which controls power to the head and tail lights and the turn signals and gauges.
The 2nd fuse down feeds the brake lights, oil pressure switch and horns.
The 3rd fuse down feeds the ignition circuit.
The 4th fuse down is the main fuse. It is fed from the starter relay, which is connected directly to the battery. The regulator/rectifier also feeds the battery through this fuse, so make sure the contacts are clean and the fuse is good.
The bottom fuse only protects the ACC outlet at the bottom of the fuse panel. That should not have any effect on charging.

[pasteurized]

Hey Steve, thanks for the input. I will check all the fuses I can either tonight or tomorrow. I looked all over for a fuse box like my '82 GS650 had, and I cannot seem to locate one. The fuse that was blown was right under the left side cover, inline and it looked factory stock. Is there actually a fuse box on a '77 750?

[SPARKSS]

Electrical problems, arrrgh!

Hopefully you won't grimace at my reply......having gotten "caught" myself a couple of times over the years. Any chance you bumped the kill switch (which can even hang half-way and on a quick glance look ok???? I've almost never used it on any bike I've owned and noted you didn't mention it when going over what you tried.

[pasteurized]

Heh, yes, I have checked the kill switch as well. In fact, I played with it a bit, switching it on dims the cluster lights ever so slightly, so I know it is engaging the "running" circuit.

[Steve]

Can't tell you where the fuse box might be as the 750 is one size I have not yet played with. My son has had a 450 and 650, my wife has an 850 and a friend has a 550, and they have all been pretty much the same for fuse arrangement in the fuse box. The box has moved around, but the arrangement is the same.

.

[edbot]

The 77 750's don't have a fuse box. Just the one fuse behind the left side cover.

[pasteurized]

Damn, that's what I thought. Thanks.

The 77 750's don't have a fuse box. Just the one fuse behind the left side cover.

[earlfor]

My first inclination is that the increased amperage consumption of the louder horns burned the contacts in the ignition switch. I suspect you "toasted" the ignition switch.

For installing a horn with a higher power draw, a relay is required.

E.

[argonsagas]

I see Earl has already replied with the answer.



Connecting a powerful horn to the circuit directly will almost invariably blow the fuse due to the much higher electrical draw non-stock horns demand, thus the requirement for a relay to operate it.

The wire feeding the horn is a tiny one, (22AWB) and it goes through three splices within the harness before reaching the horn, so it cannot handle much current load and if you keep trying it, or use a larger fuse, you may overheat the wire and damage the harness.


Since you are constantly draining the battery, you might also look at this:

Your horn does not get a "live" feed at the switch. It is the opposite, with the circuit into the horn always live, and the switch providing the ground.

[pasteurized]

I understand what you two are saying about the horn drawing too much amperage. When my friend suggested it, I immediately told him that would be the case but he insisted that it would be fine, and sadly, I listened to him.

Any way to test if the ignition switch is the culprit? I get all the lights on when I turn the key, and it cranks like a champ when I hit the starter button...?

[earlfor]

The starter doesnt draw power through the ignition switch. Only the exciter wire to operate the solenoid goes through the ignition switch.

I would look at a wiring diagram to determine which output lead from the switch powers the coils/ignition system. Check the lead for voltage with the switch on. Sometimes, there can be continuity/12 volts output but no amperage. Whether the lead shows no voltage or 12v with the bike not getting ignition, at that point I would jump that switch output lead directly to battery positive. If the starts/runs normally, its a pretty safe bet the fault is in the switch. Or, if you happen to have a spare switch, swap them out and see.

E.

I understand what you two are saying about the horn drawing too much amperage. When my friend suggested it, I immediately told him that would be the case but he insisted that it would be fine, and sadly, I listened to him.

Any way to test if the ignition switch is the culprit? I get all the lights on when I turn the key, and it cranks like a champ when I hit the starter button...?

[argonsagas]

I am not certain of the wiring on this model.

I would take Earl's advice and check out the switch as well as all connections.

If you cannot resolve it that way you may have to go a more difficult route.

Logic is this way:
Power runs from the fuse box to the ignition switch.
When the switch is "ON" power runs through the switch to the kill button and also to the starter button, as well as to the ignition circuit and lights, although this is likely done through different contact positions inside the switch.

The kill switch controls the ignition circuit, and it is separate from the starter switch, so if If power is available at both the kill switch and at the starter button it should also be available at the ignition circuit.

Apparently it is not, so there must be a break in the circuit after it leaves the switch.

You must check all connectors along the route. Hopefully, you will find one loose and resolve everything. Remember to check both sides of each connection. I think you have a points ignition, so be sure you check input voltage there, and check for voltage at the coils.

Use a meter and look for voltage all across the ignition side. If you have a substantial drop, it may just be a dirty contact, which can be fixed by cleaning. This is not uncommon, and the voltage drop could be the reason for non-firing.

If none of these, and you have thoroughly checked all available connections and fuses, you may have is a problem at one of the junctions inside the harness, relating to the tiny wires that run to the horns mentioned earlier, as they are spliced into several parts of the harness and those tiny wires can overheat easily when too much amperage draw is run through them.

If the splice point got too hot it may have opened a contact, or melted and broke it.

Hopefully, this will not be necessary, and it is a pain to do, but a careful slicing of the harness tape may be all you need to find the connections and repair them.

[pasteurized]

Update time... aka, HELP! ;-)

Got to spend some time on it this afternoon. Opened the right handlebar control and checked the solder point from the off/run switch, tested fine. Tested the orange wire that runs from the on/off switch to the coils, tested fine at 12V at the point which they connect to the coils. Next, I checked the points; with ignition on and run rocker switch on, I got 12V to each of the points (when not making contact with the plate). Additionally, checked the wires that run from the points to the coils, and when I got 12V at one of the points, got 12V at the end of the wire where the coil would connect to the corresponding contact point. All ok there. Tried to check for resistance of the coils, but had a hard time getting a good reading. The readings I did get were in the low 4s. But like I said, I don't have a whole lot of confidence in those readings.

One thing I did notice is when spinning the motor over with the starter, I didn't seem to be able to see much of any spark coming from the points when they made contact. I was, however, able to take a screwdriver and move it around between the point and it's striking area and with the ignition on, get it to spark with the screwdriver. No real visible spark on its own though when cranking the motor over.

No spark whatsoever out of the plug wires. I tried a lot of different things. Disconnected and reconnected the wires going to them, replaced one of the coils with an extra I have, even ran a separate wire from the 1-4 cyl point directly to the coil, bypassing the wire in the harness to see if that had any effect. None whatsoever.

Kind of really stuck at this point. The coils are getting constant power from the off/run switch, getting 12v from the points, points don't seem to be sparking much (but apparently are doing their job?) and no spark at all from the plugs. I guess that leads to the coils being bad, but then why didn't my replacement coil fire the plug I connected to it either? Maybe if someone can better explain how the coils/points are wired, I could see if there is something I am missing?

Any input would be great, as I am up in arms here.

[pasteurized]

I'm pretty stumped, earl (or anyone else!) have any suggestions on where to go from here? I will be going over there tomorrow afternoon to do any other testing I can think of.