XJ650 Maxim Main fuse blows when ignition is off

Hey folks,

Bought a used xj650 maxim that was meticulously maintained. I checked and swapped all the fluids, and got everything dialed in. I rode the bike for a week with no issues until yesterday. That evening when I went to start the bike, I got no electricity except for the neutral light popping on.

I checked the battery, it was at 12.4 volts. I popped the seat and the 20amp main fuse had blown. I replaced it, but as soon as I popped the tube into the cradle it immediately blew. The key was out of the ignition and the bike was in the lock position. I tried it with a few other fuses, same result. They would pop without me even turning the bike on.

I spent the last few hours unplugging every connection and testing the fuse with a 20amp circuit breaker. I got clicks even after going through every last plug on the harness. I pulled the headlight and double checked all the wiring in there, unplugging everything one by one. It looked really solid with no tears or real wear. The only time I didn't trip the circuit breaker was when I disconnected the regulator. However, there was no power passing through the 20amp main circuit while the regulator was disconnected.

I don't know a whole lot about electrical systems and I feel like a 1st grader trying to read shakespeare when i trace the wiring diagram. Where should I be looking for the short? Could the regulator be the issue? Am I reading the wiring diagram right by thinking that the short has to be somewhere in the connection from the 20amp main fuse to the ignition?

I'd appreciate any bright ideas or avenues to explore. Thanks for the help!

 

unplug your ignition switch and regulator put in a fuse.
the 20 amp fuse sends voltage to the ignition switch and regulator only.
if the fuse still blows you could have a pinch in the wires on the way to the ignition switch/ regulator.
with fuse out and switch unpluged, using a multimeter on ohms one lead to the output side of the fuse or the wire at plug, one lead to ground checking for short you should get no reading. if you do get a reading your regulator could be bad.
if you get no reading unplug reg and plug in switch and test again.


what do you mean by locked off or in the park position ?

 

"The only time I didn't trip the circuit breaker was when I disconnected the regulator. However, there was no power passing through the 20amp main circuit while the regulator was disconnected. "

this makes no sense should still be voltage at the connector for ing switch and reg connector

 

Vr could be internally shorted?

 

this is wiring diagram i am looking at
http://members.tripod.com/dave_jack/wiringdiag/d7a.jpg

http://members.tripod.com/dave_jack/wiringdiag/d7b.jpg

on D7b diagram follow red wire from fuse 7 forward it goes to second page d7a where red wire splits off and goes to regulator and ingnition switch.
when you get to switch follow blue wire back it connects to tail light and lic plate light.

the brown wire(i think it is brown) brings voltage back to the rest of your fuses, it also goes to a relay(33) and brake light (30) and horn switch (29)

pop out the rest of your fuses and you will only have to check what is listed above

 

that is what it sounds like to me too. if he disconnects the ignition switch and still blows fuse
it is VR or pinched wire

 

Svendovian
to trouble shot electronics you need to learn to isolate circuits. that is what you are doing when you unplug things. in your case where it is the main fuse blowing, you need to start by removing all fuses but the main fuse.
the main fuse supplies the voltage to , the voltage reg., and ignition switch.
the ignition switch supplies voltage to the tail lights with the blue wire, the brown wire from the ignition switch supplies all other fuses with voltage and it also goes to a relay(33) and brake light (30) and horn switch (29)
print up a copies of your wiring diagram and get some diffrent color high lighters.
use the lightest one to highlight the circuit you are testing as you test it. after you test it go over it with a different color.
get a yellow blue and red highlighter.
yellow first when done use blue over yellow it turns green.

 

forgot to give you this component key for wire diagrams
http://xjdiagrams.thundervalleypower.com/wiringdiag/d8.jpg

 

Solid info. Pleasantly surprised by the quick and super helpful responses. Great forum! thanks for taking the time to explain simply. I'll update as soon as I isolate and test the indicated circuits. I'll test out the regulator as per the Haynes if the circuit tests come back negative.

 

There is power routed through the main fuse directly to the Rectifier Regulator. Therefore, it would seem you have already found your problem. You should find at least a couple of diodes shorted when you check the Rect/Reg per the Haynes manual. You will need to use the diode setting on your meter to get accurate results of the condition of the diodes, however not required to find shorted diodes.

 

Hey there Rooster,

Thanks for the lead. I checked the RR this evening, but I got totally backwards results. Would you folks mind checking my methodology to point out my rookie mistakes?

The results of the test were,





The readings I got from my Multimeter set to diode were,



I made sure that my multimeter cables were not mixed up. The black negative cable was in the COM port and the red Positive cable was in the correct port for testing diodes. I tripled checked my results. I find it odd that they are totally opposite of a normal functioning VR. I would understand if a single diode was shorted out as indicated by a discontinuity. Is this a normal reading from a VR that is totally fried or is there something I totally overlooked?

I'm trying to learn this stuff for the first time, sorry if the questions are blindingly stupid. Here is what I think I understand. The voltage rectifier changes AC to DC current in order to charge the battery during normal operation. The regulator insures that the charge remains consistently plateaued at a rate the battery can handle even when the engine revs to a higher speed. The regulator consists of a series of diodes that act as a "one way valve" for electricity, allowing it to flow through one direction, but not allowing it to flow backwards. The white wires are the anode of the VR, allowing electricity to flow in from the alternator. The positive red wire is the cathode, allowing a regulated current to flow from the VR to the battery.

I just want to make sure that I am understanding things correctly before I lay down the dough for a new VR.

Sorry for the long post.

I plan on checking out the wiring that XJ550H directed me to just in case there is a short and the VR isn't to blame. Thanks for the continued help!

 

Your readings are saying that the diodes are fine. The difference is caused by Yamaha's "pocket tester", which when set to the ohms scale reverses the polarity of the readings. It was quite common for analog meters such as the "pocket tester" to place a negative voltage on the positive probe and a positive voltage on the negative probe. The result is a diodes forward bias would appear reversed. Forward bias (o = continuity) of a diode will occur when a positive voltage is applied to the anode, and a negative voltage is applied to the cathode.

Your explanation is pretty good on the function of the diodes and understanding their purpose.

So it is a bit surprising to see good results with the diodes. I'm not sure if you reconnected the Rect/Reg and duplicated the issue, and if not perhaps the main harness red input wire to the Rect/Reg is chaffed and touching ground somewhere and the process of disconnecting the Rect/Reg altered its position.

Did you take it out of the lock position, or was it really in the park position? One of the strange things that Yamaha did was provide power to the tail light via the main switch fused only through the main 20 amp fuse. If the switch is in the park position voltage is being routed to the tail lights.

I like one of the tests that was suggested, except somewhat altered if the main fuse is blowing with the ignition switch set to off.

Disconnect the battery and ignition switch set to off. Put a good fuse in the main circuit and with the DMM set to ohms place the positive lead on the positive battery cable. Place the negative lead on negative battery cable. You should get a high reading. If the reading is low (less than 1 ohm) then disconnect the Rect/Reg and observe results. If it changes to a high state then you have found your problem. If still low then disconnect the ignition switch and observe the results.

If the reading is not initially low, it gets a bit more complicated with the ignition switch set to on or park. If you get to this point just remember that the signal bulbs tend to be a low resistance, and may appear as a short of just a couple of ohms.

 

I also meant to ask about this. Did you just get a momentary light as the fuse was in the process of blowing? If so, and the ignition switch was in park position when you were replacing fuses and they kept blowing then the tail light circuit from the output of the ignition switch becomes very suspect.

 

Reply deleted.

 

Are you sure it is a 20 amp because my Xj700 has a 30 amp main but I really I am not familiar with your bike but check on a diagram before you just throw a 30 amp in their

 

The 650 and 750 both have 20 amp main fuses. Your 700 (and the rest of the world 750 for those years (thank you Congress)) have a slightly different electrical system.

 

Oh i wish it was as simple as having too small of a fuse. Its a 20 amp for the main for sure.

I reattached the vr and put a fuse in and ran the continuity test as you suggested this morning. I got a high reading for the lock, off, and on position of the ignition without the regulator. I got a low reading in the "on" position only with the reg reattached. Doping through the wiring diagrams this morning, striking out so far.

Checking through the tail light circuitry now. So far no shorts. At the beginning of this whole problem, I went to start the bike, I didn't have enough juice to crank the engine, but the horn worked albeit very weakly and there was enough juice for the neutral light. I trickle charged the battery overnight, assuming that was the problem. When I went to start the bike after charging the battery, that's when my main fuse woes began.

 

How low was the reading? With the ignition switch on power is supplied to the IC regulator and the brushes that supply power to the field coil in the AC Generator. You might do a quick ohm check on the IC regulator of the Rect/Reg. Check the brown to black and the green to black. Brown to black should be about 2 kohms, green to black should me in the megohms. Problem with this is it would only blow the fuse if the key is switched to on, and the way I understand it we are trying to find a reason for the main fuse blowing with the key switched to the off position??

So, the only time you get a low reading is with the regulator connected and the switch set to on. Have you verified it will still trip the breaker with the key off and everything connected?

 

A real good place to look for bad wires is around the steering neck where they bend as the bars turn.

 

Visually inspected all the wires around the steering, didn't see any frays. I disconnected all of the elements one at a time in the headlight housing and still got the same symptom of blowing out the main fuse while the key is in the off position. Am I right in assuming this means that if there is a short, it's before all of the molex connectors behind the headlamp?

 

breaker trips every time with the key off and everything connected. When I disconnect the voltage regulator the breaker doesn't trip, but when I check with the multimeter, there's no electricity flowing through the main fuse. Continuity, but no juice.

Thanks for the continued tips. I'm going a bit loopy trying to track this thing down. Checking the wiring from the alternator to the VR next

 

What do you mean check with DMM there is no electricity flowing? If you are placing the DMM in current mode and placing it across the main fuse and no current is flowing, that would be normal with the key off. Don't do that in the fuse blowing mode or you might damage your meter.

With the main fuse installed, and the regulator disconnected voltage will be present at the ignition switch and at the main harness Rect/Reg mating connector. Current will then flow if there is a load, which at that point there should not be a load. Even with the regulator connected no current will flow with a working regulator, otherwise this "unswitched" power load would drain the battery on a working system.

Add this to the other Rect/Reg ohm checks suggested earlier. With the meter in the diode mode check from Red to Black on the Rect/Reg. Should get about 900 ohms in one direction, and open in the other direction. Also check Red to Brown, should be open. Did you do the other ohm checks suggested earlier?

 

dmm can check for voltage, current , and continuity, some can check for more.
for voltage black probe to negitive on battery red lead to where you are checking for voltage.
for continuity place one lead to each enr of wire
for current leads go in series with the item being checked .

 

One of you electronic gurus should do a "How to use a Digital Multimeter To Test a XJ w/pics" for the DIY forum or is there already one.

Gary H.

 

chicken or the egg. how to use a dmm or how to read a schematic.

 

How to use the dmm. I'm seeing a lot of the same testing procedures and information in various threads.

Gary H.

 

Done: http://www.xjbikes.com/forums/threa...nd-read-schematics-and-wiring-diagrams.68164/

 

Brilliant. Thanks.

Gary H.

 

After a few weeks of trudging through the whole dang electrical system, I finally brought it into a solid local mechanic. Turns out that the voltage regulator is internally shorting somehow. Even though all of the diodes checked out, the VR is grounding out. Mechanic said he's never personally seen the issue before.

 

That has happened before but not very often. My first thought was that regulator when you reported blowning the fuse with everything off.

 

Ask him to take a peek at the earth ground. See if it's making good contact through the frame paint.

Gary H.

 

I'll make sure to take a look at the ground contact. I thought it was the VR initially too, but when the diodes all checked out, I figured the problem had to have been elsewhere