XJ 550 Maxim Diagnosing Electrical Short

I bought an ' XJ550 Maxim that didn't run as a project. When I bought it, the main fuse was blown (I didn't realize until I got it home). I tried replacing it, but when I hooked up the battery, it blew even without keys in the ignition. I tried to disconnect the regulator and hooking up power to see what happened. Nothing happened until I turned the ignition on and then only the signal fuse blew. I left the blown one In there and connected the regulator and found it still blew the main fuse. I replaced the main fuse again but left the blown signal fuse and disconnected everything that the Signal fuse is wried too except the ignition switch, alternator, and neutral light. Did this using that one wiring diagram and the brown wire. Doing this didn't make a difference it still blew the main fuse once I plugged in the regulator.

I know the fuse box is usually the first point of attack on these for electrical but I figured it wouldn't be causing a short like this. Please leave me any advice for finding my issue!

 

I would suggest you have two problems, the first being the main fuse (20 amp) blowing, which you already isolated to the Rect / Reg assembly by disconnecting it and the main fuse did not blow. If it were mine I would do the diode check from the FSM just because I like to verify parts are bad before replacing. If the diodes look OK then check from the Brown input to black wire

The signal fuse (10 Amp) is a different issue and either you haven't gone far enough in disconnecting items or there is a signal wire that is somehow shorted to ground. How did you disconnect the brake lights, did you disconnect both the front and rear switches? Unplugged at the flasher relay and cancel unit? Disconnected at horn?

 

Thank you for the advice. I felt there might be 2 issues, but I also know the rectifier connects the Red wire coming from the main fuse to the brown wire that connects to the signal fuse. This makes me think either the rectifier is also bad or it is just extending that brown wire issue over to the main fuse through the red wire. Please correct me if that isn't actually possible.

How do I do a diode check? I'm sure there's something on this forum but could you point me in the right direction?

What do you mean by brown input to black wire?

Yes, I disconnected both the front and rear switches, unplugged both the flasher and canceller unit, and unplugged the horn. The only thing the brown wire was still connected to at the time was the alternator and the ignition. Is it possible that either the ignition or alternator are my issue?

Thank you again this is a huge help. This is my first project bike so I'm learning a lot

 

It shouldn't, at least not directly. The red wire from the main fuse goes to the regulator and the ignition switch. The output of the ignition switch is a brown wire that feeds the other 3 fuses, Head, Signal, and Ignition. The signal circuit just happens to use the same color brown wire, and would only be connected to the red wire via the ignition switch and signal fuse

Follow step 2 in the attached to check the diodes - red to white 3 places and black to white 3 places, each of which will show a diode

A DMM connected to the unplugged rect/reg connecter between brown and black should not show a shorted circuit, and may as well check red to black while you are there

Disconnect the battery, signal fuse out, and with everything disconnected as stated connect a DMM set to auto or 200 ohm range from the output of the signal fuse to chassis ground. This should read open. If you have a direct or near short to ground then look for a chafed / pinched wire

 

You have been very helpful thank you. I tried the diode test which it passed but when I checked the black to brown on the unplugged rec/reg like you said it came up not open. Would 3.6 Kohms resistance be a short? I’m assuming anything that isn’t open in this case is but wanted to check before I buy another rec/reg.

 

No, that shouldn't be the source of the problem

Are you disconnecting two connectors above, as in the Rect/Reg and brush assembly?

 

No, just the one connector to the rect/reg. I'm assuming you meant brake assembly. If you did, I'm not sure which specific connector you're talking about, sorry.

Also I did that resistance test from the signal fuse output to the chassis ground and it didn't come up shorted which leaves me all the more confused.

 

No I meant brush assembly because it uses 12V switched that is fused only by the main fuse. It's a two pin connector; I am not sure where it is located on the 550.

So the next step then would be to reconnect the assemblies one at a time and look for a short. I am not sure if you actually replaced the signal fuse and blew it again at any time, so if nothing appears shorted with it hooked back up disconnect them again. Then, with a good signal fuse test with battery connected ignition switch on, then connect each one individually and see if the signal fuse blows - leave the Rect/Reg disconnected for this test

 

If you find the price of fuses a pita when testing, a good trick is to put the signal light across the fuse terminals in place of the fuse. With everything switched off or disconnected, there should be no light. As you add circuits, the faulty one (with a short to ground in it) will light the test lamp instead of blowing yet another fuse.
TIP: The cheap fuses from the Land of the Silken Promise are crap. They'll burn your bike / house down before blowing.