Fuse rating for kill switch kickstart only

pablohoney

pablohoney

Don't Call Me Shirley.


Well the title pretty much says it all. I recently redid my 79xs650 special and I have made it kickstart only, removed the safety relay, turn signal canceler, starter solenoid, and light checker. It starts right up and everything works but after about a minute of running, the kill switch fuse blows. I have looked and can't find a short and it has done this several times at about the same time intervals after starting. Should I still be running the 10A fuse, or because I have removed so much I should put in a 15A? Thanks
 
Removing stuff should actually have removed load potential on the circuit if anything. Sounds to me like you have a high resistance poor connection causing excessive load. A short would blow the fuse almost immediately. You need to check for an accessory that is drawing that kind of current, and it will be in that circuit. You can try this by unplugging the remaining items on this circuit one by one(probably just ignition related circuits) and re-testing between. Check connectors in those circuits as well, as they may be getting warm or hot. Don't put a higher rated fuse in, since you can damage any components that may be designed to run on lesser currents, or worse, you could start a minor fire.

If it takes a minute or more, I would bet on a poor connection, or a corroded switch in the circuit, causing a high current load.
 
What condition is your battery?
I regularly blew fuse on my XS after about 5~7 miles when fluid level was low (I didn't know they would do that :eek: )
Switched to a new 'wet' battery and it's been fine since (removed all the same stuff you did, plus more and then re-wired it so everything I needed worked ;D )
Have you re-wired anything else through that circuit? (new coils, etc)
 
I would try removing that kill switch from the equation and see what happens (just hook the two wires together for the testing). It may be that with such a large switch, you are getting enough resistance through the switch itself that it might be the source of the problem. You should be able to use the standard kill switch, or one like it with no problems. Current flow through the kill switch is no more than it was before you removed all that stuff, so a heavier switch is actually unnecessary.
 
I tested the resistance through the switch and it was practically nothing. The bigger switch is probably providing less resistance than a smaller one due to the fact that the bigger the conductor the lower the resistance. However I tested the resistance through the circuit at the fuse holders, with the ignition on, no fuse and the battery terminal disconnected and I would get a reading once I touched the probes to the holder then infinite. Every time it was different, 70, 125,60 etc. Seems weird.
 
When I rewired my XS, I did it up with a single 20A (I think) blade fuse off the battery terminal and that's it. No other fuses, and a single 15A or so toggle switch is my 'key'. On/off.
 
It will be hard to test resistance with current flow through the circuit. You can test for voltage drop that way, though, which will indicate resistance. Measure the resistance with the bike turned off. This will give you the steady and accurate reading you are after. 20 amp would be more than enought for a non starter equipped XS.
 
35amp switch just means it's rated a 35 amps capacity.
The switch contacts will have close to zero resistance no matter what amperage a switch is rated at (unless its faulty ;) )
If it's blowing the main fuse there is a problem somewhere.
High resistance in connector blocks maybe?
You should have an amperage setting on meter but it may be too low to use for main fuse testing?
Depending on meter, it should be either 10 or 20 amps.
Just put the meter probes in the fuse contacts (remove fuse first)
It's a QAD method of finding total load.
55w headlight bulb draws around 4.8amps (60w=5a)
coils, around 2~3 amps each
indicators, about 5amps
brake light, ~1.2A
instruments and side lights, 1.5A plus some losses in wiring, total around 20A if you run everything through one fuse (Indicators are intermittent, as are coils when running)
I would probably try a 20 amp fuse but have a couple of spare 25A.
!5A is fine as long as you don't switch ignition on with indicators already turned on, total load will burn out a cheap 15A fuse
 
Use the original fuse. Here is the reason why. The fuse is not there to protect the end user, it is there to protect the wire. You determine the size fuse you are using such that you won't burn up the wire if there is a short. Wire size (standard stranded automotive copper wire is determined by the demand of the end user and length of wire required. While you have got rid of at least one big load in your system all the rest of the wires are essentially stock and so that fuse that was sized to protect the bike's system when it was called stock is still appropriate now that the same system is in a modified bike.
 
crazypj said:
35amp switch just means it's rated a 35 amps capacity.
The switch contacts will have close to zero resistance no matter what amperage a switch is rated at (unless its faulty ;) )
Click to expand...

True, but a lot of DMM's do not read resistance well with current flow in the circuit. They give the erratic readings he was talking about. Also, unless there is a heat issue, it should not matter how he measures the circuit, power on or off. Therefore, since his meter does not read resistance with current flow in the circuit, for heavens sake turn the circuit off and measure the resistance! THis reading will be the same and can then be applied to the active circuit.
And, very few meters have more than a 10 amp internal fuse, so his meter will most likely not work for an in-circuit current test. Without a lot of screwing around to measure each portion's draw separately, and given that there are only a few components on the bike anyway, it will be much faster to just disconnect a single item at a time, turn it on, and see if it blows the fuse. Normally I would measure the current with my inductive amp clamp in real time to avoid that many blown fuses, but I doubt he has this equipment. Therefore back to what I said way earlier, just disconnecte the few loads you have one at a time and see what changes. This should not be this hard or invoke such a discussion.
 
I too would use an amp-clamp but they are quite expensive, so, as you say,doubtful he's got one.
Long-winded discussion is due to fact very few people understand vehicle electrical systems.
I don't think any of the information is conflicting, just trying to explain how and why tests are done.
Simplest thing to do is replace fuse with a bulb, clip onto fuse connectors with fuse removed, then start disconnecting components. (use a signal light with alligator clips)
When bulb goes dim you've found the short (if it goes out you've disconnected all ground paths, even the ones through a load)
Could also make a shunt from 8 gauge cable.
Set meter to millivolts and at measure 19.1" (probes through insulation) cable length doesn't matter
Milli-volt reading is same as amps in circuit
 
I tried checking the the amperage through the circuit and at 2.4A with just the ignition on and between .2 and .8 with the bike running. This normal?

Also I am not getting any continuity through the circuit with the battery disconnected and the ignition and kill switch on closed. Although i get amperage through there when I connect the battery. How does that make sense?
 
I taped whats going on. This was the second fuse in a 5 minute time and there was still the delay so it doesn't have to do with heat. It was running for about a minute before this:

 
Looks like a huge amp jump just before the fuse blows. Does anything turn on or get used right at the end of your video? Something is turning on or connecting and drawing more than than the fuse is rated for. Is it possible that your voltage regulator is shorting to ground when it begins to reduce the charge rate to the battery? Try unplugging the R/R and see if it still blows. It could be that it is fine while the charging system replenishes the charge used to start the bike, and when the R/R starts to shunt the charging system to ground, something is damaged in the R/R, shorting the ignition hot circuit to ground. That is the only thing I can think of that might be "switching" at that kind of time interval without any input from you.

Beyond that it looks like very low current draw in the circuit.
 
Well that sounds Good to me. It is a separate rectifier and regulator sure I won't break anything by disconnecting them?
 
Just disconnect them both at their respective plugs. Your charging system will simply be inoperative. You won't need to run it real long to find out if it has fixed it or not. Nothing else should really change that I can think of...Let me know how it goes.
 
I think T71 has you on the exact right track. I think your rectifier is pooched. I don't have the specific stats on hand but if you want I can put up the resistance numbers that you need from the rectifier. Google 650garage, great forum search it and you'll learn everything that you didn't know you needed to know about the charging systems on these bikes.
 
You could also try isolating the stator entirely, left side cover of the engine, look for a bundle of black wrapped wires that terminate in a ( should be I think ) eight port white plug up near the backbone of the frame. Dead short in the coils of the stator could cause your symptom. You could also try disconnecting the battery completely and any grounds that you have on the bike, check the resistance of your positive line to a bare spot on the frame. If you have a dead short on a positive wire it will give you a low resistance number - you should under ideal circumstances have infinite.
 
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