Blown ignition fuse

So, a few weeks back, I started having electrical issues with my bike, I have spent what little free time I have either dissecting the bike, or searching online for similar issues. The problem as it currently stands, is that when I turn the key, the 10 amp ignition fuse blows. I cannot find any bare or crimped wires anywhere on the bike, when I disconnect the TCI box, the fuse remains intact. Could there be a wire somewhere I'm not finding? Should I test the ignition coils? The pickup coils? Is there anything else I should look at? From what I can tell, the TCI box is kinda spendy to throw money at without knowing for certain that it's the issue.

Really new at vehicle repairs here, and trying my hardest to learn. Sorry if I am using various terms for the same thing, my head is spinning a little from reading up on this.

 

Did you check inside the headlight bucket for any bared wires that could short out?

 

I have looked inside the headlamp, and there are no bare wires so far as I know. Not sure if it's related, but I did recently (just prior to this issue being found) chop off the plugs on the ignition switch wires, and the three white wires going (I believe) from the alternator to the rectifier. Replaced them with bullet connectors, as they had melted the original plug ends together. I know, I have a mess of a bike right now.

 

So, as far as I can tell, the cause is most likely a fried ignitor unit. Before I sink $100+ into a replacement, I ask: would this cause the ignition fuse to blow with only the key turned on and the starter switch NOT pressed?

 

Turning the ignition switch to on with the stop/run switch set to run applies 12V to the TCI, so yes a shorted/damaged TCI would cause the ignition fuse to blow.

Nice link for wiring diagram found here on the forum, thanks to jonrms:

http://www.maxim-x.com/pix/electrical/m ... m+plus.pdf

You could do this for verification:
Remove plugs from the TCI to ohm TCI input power
On the smaller plug on the TCI place the positive DMM lead on the TCI terminal that mates with the R/W wire on the harness
On the smaller plug on the TCI place the negative DMM lead on the TCI terminal that mates with the black wire on the harness
Nominal resistance reading is 1143 ohms using a Fluke 77, may vary somewhat with other meters but a very low reading, say less than 100 ohms would point to a defective TCI. Also, since there are active components inside the TCI this is not an absolute – it may read normal and still have an issue with excessive current under normal operating conditions.

Check switching transistors for shorts:

On the smaller plug on the TCI place the positive DMM lead on the TCI terminal that mates with the orange wire on the harness
On the smaller plug on the TCI place the negative DMM lead on the TCI terminal that mates with the black wire on the harness, should read open
On the smaller plug on the TCI place the positive DMM lead on the TCI terminal that mates with the gray wire on the harness
On the smaller plug on the TCI place the negative DMM lead on the TCI terminal that mates with the black wire on the harness, should read open

If readings are normal at approx 1143 ohms and the switching transistors ohm OK:

Disconnect battery positive and negative
Connect DMM positive lead to battery positive cable
Connect DMM negative lead to TCI small mating plug gray wire, should read approx 3.5 ohms
Connect DMM negative lead to TCI small mating plug orange wire, should read approx 3.5 ohms

Note: for the two reading above you are checking ignition coil primary resistance and associated wiring and switches. The ignition switch must be set to on and stop/run switch set to run to obtain the readings. A low reading would be required here to cause a blown fuse, therefore I would recommend a test lead be made to ensure a good connection with the harness mating plug – a proper size spade terminal with a wire crimped in it to connect the DMM lead works fine.

Primary resistance per FSM should be 2.5 ohms +/- 10%, higher readings will occur from connectors, switches and lead / wiring resistance.

Other info:
Normal ignition fuse current when key is turned to on and the run switch set to run is approximately 3 amps and drops to .24 amps after approximately 3 seconds. The higher initial current is from the TCI pulling the orange wire low at power up providing a current path through 1 and 4 coil primary. This is the reason for the occasional backfire that occurs on a flooded bike several seconds after the key is turned on as the coil fires on 1 and 4 when the current is interrupted.

1982 XJ750RJ Seca used for evaluation

 

This has to be the most comprehensive check I've come across. Thank you. Unfortunately, I can't get to the bike again until Thursday.

 

So, I feel that I may have grossly misdiagnosed the bike, though I still have the issue. I have started over at square one. I pulled off the fuel tank, and have systematically removed all of the wiring that does not prevent the fuse from blowing (theoretically should not be associated with the issue if the fuse still blows without it connected). This leaves me with the following:

Instrument cluster
I have not removed any of these wires.

Headlight bucket
a 4 wire plug containing 2 red with white tracer, 1 black, and 1 blue with white tracer
red with yellow tracer
3.5 wire plug containing 2-into-1 blue, 1 red, 1 brown***

Under the seat area
battery
main fuse
2 jumper bolts associated with the starter
ignitor box
3 white wires (can be seen in the pic with the ignitor, in the background)


*** recently had to cut off the plug on the connector in the headlight bucket due to it melting together, thinking this may be an area of concern


I am hoping that someone can help me narrow down what/where to look. I am fairly confident it is not a wiring short, but I don't know what these wires are for.

pics for assistance http://imgur.com/a/KtGcw#0

 

It's been a few days because of site upgrades, hopefully you have it working by now.

I had to go through the password reset function to get logged on again if any one else is wondering

The Red/Brn/Blue is the ignition switch. Not sure about the other, the Starter switch has 4 wires, a Red/Yellow, Blue/Black, Blue/White, and Black per the FSM I have available so it doesn’t quite match.

So other than the TCI and wiring the other items that are powered via the ignition fuse are the Sidestand Relay, the Starter Circuit Cutoff Relay, and the Ignition Coils. Since the fuse was not blowing with the TCI disconnected, one would have to speculate current through the ignition fuse is above normal with the TCI disconnected, and with the added current of the TCI when it is connected, then the 10 amp limit is exceeded and the fuse blows.

This would be a simple check:

Disconnect the battery
With the ignition fuse removed place the positive side of a DMM to the output side of the ignition fuse terminal. Kill switch set to run.
Place the negative lead to chassis return – large black battery cable should work fine.

Note: The output side of the Ignition fuse is the side that does not have 12V on it with the fuse removed. Or, the input side can be identified as it will ohm to the large positive battery cable – in both cases the ignition switch would be set to on and the main fuse would need to be installed.

So you should get a reading of at least 10 ohms, depending on what the coil resistance is for the two relays and the position of the clutch and sidestand switch. I get a reading of 25 ohms on the 82 XJ750 Seca, which has a very similar hookup in regards to the ignition circuit.

Normal resistance for a Sidestand Relay coil is 100 ohms, which is only 120 mA.

If the reading is low, say somewhere less than just a couple of ohms or so, then while watching the meter remove the Sidestand Relay and Starter Circuit Relay and see if the resistance goes up. Since the ignition coils also have 12V applied to them if the reading is still low then they can be disconnected to see if the reading changes.

It is also possible that a relay fault condition may only show up with power applied. So if the readings are normal, it would be worthwhile to use a fault isolation to disconnect the Sidestand Relay, Starter Cutoff Relay, Ignition Coils and power on and see if the ignition fuse blows. Then connect one at a time until the fail is duplicated.

Plan B (the most accurate but more risk) would be to configure the bike into a condition where the fuse does not blow, such as the TCI disconnected if this is still true. This way you know you are drawing less than 10 amps. Turn the ignition switch on and kill switch to run, and then place a DMM in the current mode (most are limited to 10 amps) and place the leads across the sockets for the ignition fuse and see what the actual current reading is while the TCI is disconnected. Best guess it should be less than 1 amp at this point. If it is higher, particularly up near 7 or 8 amps then disconnect the two relays and the ignition coils looking for current to drop to less than 1 amp

In the Plan B configuration if there is a higher current than expected, especially if it is up around 7 or 8 amps with the TCI disconnected, you can try the touch test on the 4 components (2 ignition coils and 2 relays). Just be careful, as you might leave a fingerprint impression (burnt skin) on the defective component. Eight amps of current would equate to 96 watts being dissipated, so that would produce significant heat, particularly in something as small as a relay

 

Well folks, after much aggravation, I gave up on self repairs.After a long winter of not riding, I finally got my bike to a repair shop. He's been looking at it for a few weeks now, and it looks like the TCI box I picked up last fall may also be faulty. He said that he thought he had seen a place online that built new ones. I can't seem to find it. Unlike last fall, selection is pretty slim right now for an XJ700X ignitor box, anyone have any thoughts or recommendations? He is almost certain that the TCI is the issue, but I don't feel like dropping a chunk of cash on another potentially faulty part.

 

We do have used TCI's available, tested on bikes for proper operation. Drop me a note for more info.

 

Ok folks, time to pick your brains again, after testing out a certified ok TCI box, we are still getting the same readings as the original. My mechanic has narrowed it down to the fact that the fuse only blows when the smaller of the two connectors is plugged into the TCI. At this point he can only think of 3 options, 1) the TCI's are all bad 2) the wire running up to the blinker box is causing an issue, as if the blinker box is reducing the electrical flow 3) he has no idea what is another reason for the bike's issues.

Any more thoughts? Please help, I haven't ridden since last fall, and the itch to ride is really bad with the current weather.

 

Picture from your Sep 17 post. The blue vinyl tape on the small plug on the TCI indicates it should be hooked to the side stand relay, not the TCI. I don't own an XJ700, so not sure of the exact location of the side stand relay and if this is really possible. Typically though, the blue on the harness will match the blue dot on the relay. I think most TCI connectors are coded with red vinyl tape.

From Lens Catalog:

"Identification: the Sidestand Safety Switch Relay is a small square metal "cube" relay, has a blue paint "dot" by the locking tab, and has the following 4 wires connected to it:

- XJ550 all models, 1982-84 XJ650 all model, XJ700 all models, XJ750 all models, XJ900RK Seca models, and XJ1100 models: a solid black wire, a red wire with a white tracer stripe, a black wire with a white tracer stripe, and a blue wire with a yellow tracer stripe.

NOTE: original relays were always a square metal can style, although they may have been replaced by an automotive style plastic relay."

I can't quite make out the color of the wires as the resolution of the photo is not quite good enough.

 

Looks ot me like they are:
R/W
BLU/Y
BLK/W
BLK

 

First off, thank you all for your assistance. Secondly, I'm sorry for how long it has taken me to close this up. The day after Rooster and K-moe last posted, I checked the wring, and that was indeed the issue. I feel like an idiot. I had previously reassembled the wiring in the light of dusk, and it never occurred to me that two plugs, that close together, could be the same size.

Thank you all again.