leaking current

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Aug 24, 2005
This is a question for the electrical guru's. I recently rewired my '74 850 using a minimalist wiring approach, I have relays for horn, headlights and ignition.The battery holds a full charge for about two days, on Sunday I measured 12.6 volts across the terminals, Tuesday it reads 1.6 volts.My question is : where should I begin looking for the drain,the grounds appear to be good, on the cylinder head and on the gusset plate below the front of the seat. Any and all help will be much appreciated.
Thanks. James.

It's not a defective ground, not in the normal sense anyway. You have an unwanted high resistance path to ground somewhere giving you the current draw from the battery.

At the risk of telling you things you already know..... Try putting a twelve volt low wattage bulb (like the one illuminating the speedo/tach) in series with the battery. Leave the switch off. Disconnect the hot wire from the battery. One side of the bulb should be hooked to the hot side of battery, usually negative, (unless the electrical system has been reversed), the other side of the bulb to the lead you disconnected from the battery. The bulb should now glow, maybe somewhat dimly. Start disconnecting the electrical components, one by one, until the bulb goes out. Viola! You've now found the offending component. I doubt if it's a bare wire touching the frame. This would pull the battery down real quick. You mentioned relays. Possibly you have a relay that's got power to it with the switch off.

If the above fails, you may have an internal drain in the battery itself. Try disconnecting a fully charged battery for a couple of days and measure the voltage.
Well a minimalist approach is a good thing. A simple way to find the draw is using a lamp interrupting the ground wire to the battery. Battery recharged of course. If you don't have one already get a female socket from an auto store for a turn signal or tail side marker whatever. Get two alligator clips and put them on the wires that come on the socket. Clip one on the battery ground and the other on the main ground wire. This single ground wire should be going to the single point ground on the frame normally the bolt that used to hold on the rectifier. You don't want a pile of ring terminals on your battery ground leave the single point ground for this.
Now as you know no power can go out without the battery ground hooked to the system as it is. So turn your thinking inside out and you will come to see that the only way the bulb will light when interrupting the battery ground from the system to the battery is that a power wire has found unauthorized pathway back to the battery. Now you unplug each power circuit one at a time till the light goes out that's the one.
Now you say you relayed the ignition, horn and headlight? There are many possible ways of doing this and you talking about how you did it might help others reading this. You need to speak in terms of pathways for the power and how the power returns to the battery. Telling others how your system works might lead you right to the problem as well.
As an example when I add a relay for the horn I run wires right from the battery Positive and negative up to the relay on the power side normally 1/4 spades, it's got power all the time no interruption but no draw till it's tripped. Then I run the horn button wires to the relay normally 3/16 spades. Now here were it can get a little strange. Some horns are grounded to the frame and the momentary switch provides power to the horn but others have power all the time and the momentary switch provides ground. The relay doesn't care witch way around it's wired it just needs a trip to set power to the horn. Now the wiring between the switch and the horn normally would be handled in the headlight harness Do you have a headlight harness? The possibilities are endless because the same two wires from the battery are spit three ways also giving power to the relay for dim and another relay for bright. The switch wires for bright and dim go to these relays but the head light doesn't work unless the switch on top of the head light is flicked on. So tell us a little more about how your electrons go round and round maybe some can learn something.
Thanks to both JimC and norbsa, good info.,I'm a bit confused though, JimC you say hook up a bulb to the hot side, norbsa you say hook it to the ground ?. I have a ground wire running from the battery to a point on the gusset plate as I explained, I also have some of the ground wires returning from components to the battery ground terminal.What is the cleanest method,I think that I remember norbsa posting a photo. of a braided ground attachment to the frame. My relays have 1/4" spade connections, also normally open / normally closed options, I have not yet looked closely but is it possible for this to be a problem -- if I have hooked up to normally closed instead of normally open?. All of the systems work from their respective handlebar switches. Each circuit is seperately fused so pulling each fuse in turn will isolate the offending item. yes ?. Thanks much again.
No need for confusion my method simply looks at all the power in the system as it returns to the battery. There are no circuits without a ground return so no ground on the battery no drain.
The engine ground strap that I use is put on in place of plain wire because my engine ground wires broke on two different Norton's. A clean separate ground path from the engine to the common ground point is important on a Commando because of the ISO's.
All the separate grounds should return to a spot on the frame and then one heavy red wire is run to the positive of the battery from this spot. Extra ring terminals on the battery just help promote corrosion.
Again since you have made your own harness take some time to explain how the harness works. Does it use a simpler version of the headlight harness? How is it simpler and what have you saved on. You see I don't find lots of extra wire in the stock one once you remove the redundancies from the change to a Podtronics and an E.I.. Yes the relays must work in the circuit you have put them in that is why I was leading you to the horn and how it can work.
Going back to basics for a minute, if you disconnect the battery and leave it for a few days does it retain its charge?
JimC you say hook up a bulb to the hot side, norbsa you say hook it to the ground ?

It doesn't make any difference, as long as the bulb is in series with the battery. One side of the bulb must be connected to the battery, the other side of the bulb to the wire that has been disconnected from the battery, either hot lead or ground lead. If you have more than one hot lead, it may be easier to use the ground side if it is a single lead.

You can look at this test as looking for water running through a pipe. The bulb is your visual flow indicator.

Dave's right on about checking the battery first, though. It may be leaking internally. Lead/acid batteries are prone to developing internal shorts.
Many thanks to all who offered advice. I connected a bulb as directed, hot terminal to hot lead, not a glimmer from the bulb, tried another bulb -- just in case!, not a glimmer -- this battery is fully charged.I noticed in looking at the fuse panel and the close by ignition relay, that I had connected directly from the fuse panel to the relay, could this be the culprit?. Part of the reply from JimC indicated that power directly to a relay may cause the problem. I guess that I need to run wire to the ignition switch then up to the relay?.
The complete wiring harness includes relays for horn, headlight -- hi and low beams, and ignition. Using the relay wiring diagram -- hot to #30, ground to #85, power out #87, wiring from the handlebar switches #86, all are grounded individually back to a single point.The headlight relays share a common power supply, a jumper from one to the other.All original handlebar switch wiring is used.I included a low voltage switch from Al. Osborne in place of the original assimilator, wired in with the Podtronics rectifier.In answer to your question norbsa, I'm not sure that I actually saved anything,adding relays will help the Lucas switches hold up, new clean wire and good connections will help the Boyer ignition.The lack of bundles of wire cleans up the under tank area.
Thanks again to all who helped, I hope that the direct wired relay is the problem, I left the wire disconnected, I'll check the battery on Saturday for lost voltage. James.
Thanks to all who offered help, it seems that the problem of leaking current was caused by me directly wiring the ignition relay i.e. it always had power, still not entirely sure how that works, but the battery is maintaining the charge since I changed the wiring. James.
james said:
it seems that the problem of leaking current was caused by me directly wiring the ignition relay i.e. it always had power, still not entirely sure how that works,

A single relay will be consuming a small amount of electrical power all the time that it is switched 'ON' and although it's not that much (I measured one at about 120 milliamps) it would still be enough to discharge a small battery over a short period I would think.

The majority of Boyer ignition units should switch off after a few seconds if they aren't getting triggered by the pickup unit: http://www.boyerbransden.com/html/fault_finding.html
"The Micro-MKIII, Micro-Digital and Micro-Power units all turn off when not being triggered" so there may not be any electrical drain through the actual ignition system, - even if the power was left on accidentally?

Glad to hear you found the problem. Evidently what you had done was to directly wire the relay coil to the battery, but the contacts were wired to a switched circuit. I personally would not wire anything other than the main switch (key) and fuse to the battery. Forget about silly parking lights and horn, etc. having power when the switch is off. That way when the bike is shut off the battery is completely disconnected. If you have a zeiner regulator make certain it's connected downstream of the main switch.
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