Author Topic: Possible short circuit  (Read 493 times)

Online Rex

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Re: Possible short circuit
« Reply #15 on: 11.08. 2020 15:47 »
There's always going to be continuity across the horn terminals as it's the horn button which makes the circuit to earth and which makes the horn sound. I suggest you either put the DVM on Amps  or a small lamp and connect  it in series with the bike's wiring with the battery in-circuit and see when the lamp goes out/DVM returns to zero as you disconnect components.

Offline Swarfcut

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Re: Possible short circuit
« Reply #16 on: 11.08. 2020 16:40 »
BB The wiring diagram shows the horn to be a "one in/one out" design.  In other words one terminal takes current in, through the guts and out from the other terminal.  What you should be able to do is find continuity between the terminals, but no connection from either terminal to the horn body and from there to earth. No reading across the horn terminals means an  break in the internal wiring. A reading from either terminal to the horn body represents the source of the parasitic drain. Having read your posts again I don't think the horn unit is the problem, but you have not said that it actually works.

 Rex has a good plan there, a visual indication of current flow. Digital meters are sometimes too clever for their own good and old fashioned lumens from your low wattage test bulb may save the day.  Other suspects are the dynamo, due to  the cutout not working, as mentioned, and the brake light switch sticking and continuing to pass a small current, but insufficient to light the brake light bulb.

 Swarfy.

Online Greybeard

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Re: Possible short circuit
« Reply #17 on: 11.08. 2020 17:35 »
With the battery disconnected, set your meter to Single Ohms. Clip the meter leads to the wires that normally connect to the battery, so, you are looking 'in' to the bikes wiring. If the meter shows a reading it indicates a circuit is being made through the machine's electrics. If all switches are turned off there should be no circuit. The horn, light switch and brake switch if operated will show a circuit.

If the voltage regulator is faulty it may be allowing the dynamo windings to be making a circuit. Undo that screw on the end cap of the dynamo and (gently) pull out the two wires that are held in place by metal pluggy things. Has that made a difference?

Offline bikerbob

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Re: Possible short circuit
« Reply #18 on: 12.08. 2020 09:11 »
I have set the meter to 1ohm and connected the probes to the battery wires and the meter goes down to zero. Disconnected the green and yellow wires from the dynamo and with meter set to 1ohm probes connected to leads meter reads 1ohm. Set the meter to read amps then disconnected the earth wire from battery and placed the probes on the earth lead and the earth battery lead and it is showing 3.4 amps no  wonder the battery is dischraging. Disconnected all the leads from the DVR2 regulator still showing 3.4 amps dischage, so I reckon this rules out any problem with the regulator. Strangely this discharge is not showing up on the ammeter but if I connect the battery up as normal and switch the lights on the ammeter shows the normal discharge for pilot and head light. So I think over the next few days I will have to start disconnecting each electrical component and do an amp test each time until I find the component that is causing the problem.

Online Rex

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Re: Possible short circuit
« Reply #19 on: 12.08. 2020 10:09 »
The DVM showing a 3.4A discharge will be a lot more accurate than the bike's ammeter showing a normal discharge, so possibly the discharge is still present even with the lights switched. Have you tried the lights etc with the DVM in circuit?

Online Triton Thrasher

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Re: Possible short circuit
« Reply #20 on: 12.08. 2020 10:26 »
Measuring the discharge in amps on your multimeter is more accurate than measuring low resistances in ohm.

Also, if you are looking for leakage through solid state components, the multimeter’s applied voltage may be too low to disclose the problem.

Online groily

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Re: Possible short circuit
« Reply #21 on: 12.08. 2020 11:43 »
If the brake light is wired directly from the battery (not via the ammeter) I think I would disconnect that as your first next move and see if the discharge disappears when you repeat your last 'amps' test.
It or the horn are the most likely suspects, and you've checked out the horn. You know it's not the cut-out in the regulator, having disconnected all those wires but not eliminated the problem. The brake light has to be a strong possibility I reckon  . . . . and at least is easy to check.


Bill

Offline bikerbob

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Re: Possible short circuit
« Reply #22 on: 12.08. 2020 18:00 »
Been out all day just got back read your post Groily so went into the garage pulled the 2 wires one that goes from the rear light to the stop lamp switch and the other wire from the stop lamp switch, done an amp test and no amp discharge so I thought problem located I replaced the wires and done a test again expecting to find a discharge again but no all OK. At the moment I do not seem to have a problem everything is working as it should no amp discharge. Now I rewired the bike about 4 years ago and all wiring is new except for the 2 short wires that come out of back of the rear stop tail unit as at the time it meant I would have to remove the rear number plate unit and to be honest the wires looked OK and at sometime in the past had been replaced whereas the rest of the wiring was original from 1956. So it looks now I will have to replace those wires as maybe they are causing the problem.Looking at the original wiring diagram there are only 2 wires but on a later diagram that I downloaded some years ago there is a sperate earth wire attached one of the light unit mounting bolts. But this still does not explain why at the moment there is not a problem  when all I have done is disconnect those 2 wires and replaced them.

Online Rex

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Re: Possible short circuit
« Reply #23 on: 12.08. 2020 18:12 »
You've moved them? That's often enough to remove a chafed short. Third (earth) wire to the rear light is a  sensible mod.

Offline Swarfcut

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Re: Possible short circuit
« Reply #24 on: 12.08. 2020 18:31 »
BB  Now you've found a suspect circuit, the brake light switch is the likely cause, as the power goes to the switch first, then the lampholder, bulb, and earth return.  A wiring fault between the switch and bulb would mean no brake light.  Test the switch for operation, sticking on and a drain to earth before examining the lampholder wiring.

  If you thought this is a hard one to solve, keep away from trailer lighting boards....they defy all known laws of physics.

 Swarfy.

Offline bikerbob

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Re: Possible short circuit
« Reply #25 on: 14.08. 2020 10:18 »
Update, Spent the better part of yesterday removing the rear light bracket would have been easier if I had taken off the back wheel but managed to get at the 4 bolts only problem that I found was some previous owner had somehow snapped or cut the wire going to the stop light had had just twisted the wires together and covered with shrink tubing but it was not bared at all. Anyway renewed both tail wires and refitted. Removed the stop light switch it is an original switch and to dismantle you bend back 4 tabs and prise apart, inside it was a bit grotty but could not see anything basically wrong so cleaned it up and refitted. Everything is now back to as it should be no discharge showing and when engine running ammeter shows correct readings for lights on or off.  But am still a bit uneasy as I feel that I have not actually found anything that I could say there is the fault and I have fixed it, will have to wait and see but if it happens again I will go straight to the stop light switch to test first. Thanks again to all those who have contributed to this post.

Online Greybeard

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Re: Possible short circuit
« Reply #26 on: 14.08. 2020 10:27 »
That twisted connection with shrink-wrap sound like a possible source of a partial short if there was dampness in there. I can't recall if one of those wires are permanently live. I think the stoplight may be live to the bulb and get earthed at the brake switch.

Online Rex

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Re: Possible short circuit
« Reply #27 on: 14.08. 2020 11:12 »
No, the brake light switch has a live feed,  and when it makes it sends the juice to the rear lamp, the other side of which is earthed.

Offline azcaveman

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Re: Possible short circuit
« Reply #28 on: 02.09. 2020 02:45 »
Getting continuity with the horn disconnected and no continuity with horn connected is unexpected but not impossible. Could you take a photo of the meter while getting continuity (meter leads shorted together and with the meter at the battery terminals with batt. disconnected) showing both the meter display and it's control knob/buttons?
Meter readings and terminology can be confusing but photos tell a better story. Small sparks at 6V probably mean at least 1 amp of current but 6 watts would not produce enough heat to detect.