Topic: Strange electrical problem

[martin99]

1977 750F2.

Hoping someone might give me a few pointers where to look. Yesterday I switched the left turn signal on to pull into a side road, the bike died - no warning lights, nothing - and I coasted it to the side of the road. I waggled the wiring to the ignition switch, and on came the warning lights, I hit the starter button and off I went. When I got to work I checked that the connector block to the ignition switch was secure (it was).

On the way home it was behaving good as gold, ten miles into the ride I turned off on a sweeping left hander at around thirty mph, as soon as I switched the turn signal on the bike died again. Scarey, cars up my ass and not even a brake light to warn them I was coming to an abrupt halt. Coasted to the side again, clutch in, as I came to a near stop the warning lights came on again and the rest of the ride home was uneventful.

When I had safely pulled up outside my house, I flicked the signal switch to the left again just to see what it would do, and the bike cut out. Turned ignition off then on again, and it fired right up.

Where do I start looking? Only happens when indicating left, which has me thinking indicator switch, but when it did it the first time a waggle of the ignition switch loom got it going again.

Could a bad ignition switch do this? Is the fact that it's only done it when flicking the signal switch to the left coincidental? I had the turn signal switch apart tonight and ensured the contacts are clean. Also removed connector to the ignition switch, cleaned up the terminals and replaced nice and securely. I can't see any obvious signs of chafing or shorting in any of the wiring, all connections in the headlight bucket are secure and clean - I've not long gone through all this and replaced most of the terminals.

As it sits now it runs as good as always, I've switched the turn signals on/off multiple times and the problem hasn't showed up again so far, but it's got me paranoid. Don't want it happening again when I least expect it, and I hate not being able to identify and rectify a problem. I have got a multimeter, but don't know where to start.

Any ideas? Anyone else had this?

Please forgive me if I don't reply to anyone for a little while - it's bedtime here!

[evinrude7]

i'm not much for diagnosing electrical problems.  there are a few cats here that really know their stuff.  someone shared this interactive wiring diagram.  http://oldmanhonda.com/MC/wiring750K1.html   i found it interesting.  i don't imagine there is a ton of difference between a K1 and an F2 with regard to wiring.  maybe there is.  i've attached a print screen of the interactive with an area i circled in red.  could this be the spot in the wiring that is giving you trouble?  you mentioned waggling the wires of the ignition switch. 

[scottly]

The total loss of power without blowing a fuse would point to the ignition switch, rather than the signal switch. Perhaps turning the bars to the left puts a strain on the harness where the ignition switch plugs in? Also, my K1 switch had the thin tin cup that the plastic part with the contacts fit into come a bit loose from the main switch housing, resulting in a similar intermittent loss of power.

[martin99]

Thank you for your replies men. I'm leaning toward the ignition switch too, a waggle of the wires got it going the first time and even though the connection is good maybe the innards are not and moving the connection just got it to make contact again. I seem to remember seeing repair kits for these, I'll have to see if I can hunt one down. Don't think I'll have much luck finding an OEM switch, even DSS only list a pattern one - although if it's from him I would think it would be okay. Going to be away for a couple of weeks now so it will have to wait until I get back.

[TwoTired]

The total loss of power without blowing a fuse would point to the ignition switch, rather than the signal switch.

Totally agree.  But it could be battery cable connection, fuse clip oxidation, fuse box solder connections, and all the connectors in between going intermittent.

Turn the bike on, select the turn signal and start wiggling wires and components on the bike.  Tap on things with a plastic hammer or screwdriver handle.

When you can lose and restore power by tapping on a component, you've usually found an area to focus upon.

Cheers,

[BWC]

1978 F3
May not be related to your issue but this spring the engine would die at idle when the bars were turned to the left. In my case the main 15 amp fuse would blow.
After a bit of searching I could get it to happen by moving the wiring harness at the steering head.
Found these factory mechanical connections and one had worn through and was grounding  where the harness ran under a metal clip on the frame by the front of the coils.
May be worth checking while your in there. Bike has 18,000 km on it.

[martin99]

Thanks, I really appreciate all the tips and I'll try them all first before reaching into my pocket!

[evinrude7]

Thank you for your replies men. I'm leaning toward the ignition switch too, a waggle of the wires got it going the first time and even though the connection is good maybe the innards are not and moving the connection just got it to make contact again. I seem to remember seeing repair kits for these, I'll have to see if I can hunt one down. Don't think I'll have much luck finding an OEM switch, even DSS only list a pattern one - although if it's from him I would think it would be okay. Going to be away for a couple of weeks now so it will have to wait until I get back.

i was able to successfully repair my ignition switch by taking it apart and cleaning up the contacts.  pretty sure it's a reproduction of oem.  word of caution when you open it up cover it with a towel.  springs and balls will fly. 

[HondaMan]

Another tip for the "F" bikes (all of them) is: this wiring harness is much thicker than the other 750s where it wraps around the steering head. This causes some chafing of the wire insulation, especially when the old PVC cover has become hard, splitting into a sharp-edged blade there. It is quite common for a couple of wires in this area to become bare, touching each other lightly. If you have, for example, a poor connection in a plug (like on the Ignition Switch or the Fuseblock's plug) and a momentary short occurs at the head, it can burn a new carbon spot on the connector and heat it, warping the blade for a minute. After the short goes away, the connector blade cools off again, and things work - until the next time. A clue to all this: the voltage will be LOWER on the downstream side of this connector, so you can trace the whole bike with a voltmeter in about 10 minutes. Plug a battery trickle charger to it and kill the Run-Off switch while you do this, though.

Most of these bikes today have bad fuse contacts. This is because the clips for the old glass fuses were coated in yellow chromate, which has a 10-year lifespan. After it lets go of the metal, it becomes a resistor instead, heating the contacts where they grip the fuses. This causes the fuses to become soft (from heat) while carrying current, and a big bump can then make them fail, resembling a "blown" fuse. To overcome this, many shops switched the fuses to 20 or even 25 amp (for the 15 amp main), which can cause the bike to catch fire if a 20 amp short DOES occur, but the 25 amp fuse won't let go. To stop all this nonsense, I created fuseblocks with modern ATC fuses and brass connectors, so if yours is corroded and dark in the connectors, maybe consider one of these?

[martin99]

Another tip for the "F" bikes (all of them) is: this wiring harness is much thicker than the other 750s where it wraps around the steering head. This causes some chafing of the wire insulation, especially when the old PVC cover has become hard, splitting into a sharp-edged blade there. It is quite common for a couple of wires in this area to become bare, touching each other lightly. If you have, for example, a poor connection in a plug (like on the Ignition Switch or the Fuseblock's plug) and a momentary short occurs at the head, it can burn a new carbon spot on the connector and heat it, warping the blade for a minute. After the short goes away, the connector blade cools off again, and things work - until the next time. A clue to all this: the voltage will be LOWER on the downstream side of this connector, so you can trace the whole bike with a voltmeter in about 10 minutes. Plug a battery trickle charger to it and kill the Run-Off switch while you do this, though.

Most of these bikes today have bad fuse contacts. This is because the clips for the old glass fuses were coated in yellow chromate, which has a 10-year lifespan. After it lets go of the metal, it becomes a resistor instead, heating the contacts where they grip the fuses. This causes the fuses to become soft (from heat) while carrying current, and a big bump can then make them fail, resembling a "blown" fuse. To overcome this, many shops switched the fuses to 20 or even 25 amp (for the 15 amp main), which can cause the bike to catch fire if a 20 amp short DOES occur, but the 25 amp fuse won't let go. To stop all this nonsense, I created fuseblocks with modern ATC fuses and brass connectors, so if yours is corroded and dark in the connectors, maybe consider one of these?

Hi Mark. Thanks for taking the time to explain that. I already changed the old fuse block to ATC a year or so ago, so hopefully that's one variable I can rule out but I'll check to make sure anyway. I'm using 15a for main.

Any chance of adding some more detail to checking with the voltmeter? Like 'put the probe on this one and the other probe on that one' type detail?

Possibly unrelated but possibly not, when I took the bike for MOT (UK roadworthy test) last month the tester remarked that my headlamp, sealed beam, was unusually dim and he only just passed it. I checked everything in the headlight bucket (by eyeball, nothing scientific) and couldn't find a problem. All the connectors in there are relatively new too, in fact I've been through the whole bike replacing as many connections as I can. The battery is a Motobatt agm and not that old either. It measures 12.8v at rest at the moment.

[Deltarider]

 

last month the tester remarked that my headlamp, sealed beam, was unusually dim and he only just passed it.

If it's an US sealed beam, you might as well look for a bin. They perform poorly and simply aren't up to European standards. Fine for day riding but not for at night.