1982 xj750 fuse box wiring. Wrong color wires

Just made a trade for this bike a while back. Bike was a mess so I’m going pretty deep trying to clean everything up. Fuse box was non existent when I got it.

One set of wires had an inline fuse and looped back into the harness. The rest of them were all looped back into the harness with pretty much all the wires exposed and touching.

Went to hook up an aftermarket fuse box yesterday and I have 1 red/white wire, 1 red/yellow, 3 little brown wires, 1 thicker brown wire and 2 reds.
Anybody ever seen anything like this?

Everything I have looked up had matching pairs of wire.

I am brand new to this forum so please let me know if I need to be posting in a different place.

 

Some bikes did indeed have 3 brown "input" wires feeding into the fusebox.......the thicker brown wire is the "input wire" (from the key switch) to the headlight circuit (the red/yellow is the output wire); one of the small brown wires is the "input" to the signal circuit and one of the small brown wires is the "output" of the signal circuit; and another small brown wire is the "input" for the ignition circuit, with the red/white being the output of the ignition circuit.

FUSEBOX INPUT, MAIN CIRCUIT: large red wire, from the battery
FUSEBOX OUPUT, MAIN CIRCUIT : large red wire, to the key switch

FUSEBOX INPUT, HEADLIGHT CIRCUIT: thin brown wire, from the key switch
FUSEBOX OUPUT, HEADLIGHT CIRCUIT : thin red/yellow wire, to the headlight switch, etc.

FUSEBOX INPUT, IGNITION CIRCUIT: thin brown wire, from the key switch
FUSEBOX OUPUT, IGNITION CIRCUIT : thin red/white wire, to the ignition coils, etc.

FUSEBOX INPUT, SIGNALS CIRCUIT: thick brown wire, from the key switch
FUSEBOX OUPUT, SIGNALS CIRCUIT : thin brown wire, to the turn signals switch, etc.

Here's the basic overview of how the current flows: battery positive lead to solenoid, and the thick red wire from the battery or solenoid (dpends on model) to the INPUT of the MAIN fuse in the fusebox.

A thick red wire is also the OUTPUT from the fusebox MAIN circuit, and goes to the key switch.

Coming out of the key switch is a thick BROWN wire, and it runs back to the fusebox to become the "input" for the HEADLIGHT, IGNITION, and SIGNAL circuits.

AND HERE'S THE KEY POINT: this thick brown wire from the key switch is "split", internal to the harness, into 3 separate wires (one for each of those circuits that it will power). ON MOST BIKES, when that brown wire from the key switch is "split", it is split into 3 separate color wires: a red/white, a red/yellow, and a solid brown wire ---- so these "input" wires will then MATCH the wire colors for the output side of the fusebox circuits (and this is the logical way to do things).

HOWEVER, on some bikes, for reasons unknown and unknowable, the "split" results in 3 brown wires to the input side of those circuits. The output side of the fusebox still has the 3 different color wires (red/yellow for the headlight, red/white for the ignition, and solid brown for the signals)....but the input is "all brown" wires.

Of course, on the input side, it makes no difference which wire goes to which circuit (or even what color they are), as they are all carrying the same 12V from the battery (well, from the battery and then thru the ignition switch and down the brown wire). That wire from the key switch is the "thick" brown wire, and on some models, the thick brown wire is "split" into:

1) a thick brown wire (actually, just a continuation of the thick brown wire from the key switch)
2) a thin brown wire
3) another thin brown wire

So........first thing you have to do is identify which of the brown wires is "hot" when the key switch is on. Of course, the thick brown wire will be hot, since it's the "main" wire coming from the key switch. But you'll also have 3 of the thin brown wires..............two will be hot, since they are just "splits" from the thick brown wire, and one of the thin brown wires will be "dead" since it is actually the OUTPUT wire for the signals circuit.

So, with battery connected, and key switch on, check for power (to ground) on those 3 thin brown wires (of course, those brown wires should not be connected thru the fuse, or else you'll never be able to tell input from output!). The two thin brown wires that are "hot" are the input wires for either the headlight or the ignition circuit.

This "3 brown wires as input to fusebox" is most usually seen on XJ750 Seca and XJ1100 models, but may appear on other models, too.

You can live with it "as is", or for a more rational fix, you can dig into the main harness (un-wrap the harness tape a few inches) and you'll find the "split" (it's actually a crimped wire "ball", not very elegant!) and remove the two thin brown wires and substitute a suitable length of red/white and red/yellow wire, so that the input wires to the fusebox will be the same as the output wires..........of course, in doing so you will now have a coherent, sensible look to the fusebox system, but it will no longer match what is in the factory wiring diagram :-(

 

Ooo, that's useful
Ta

 

Chacal, you da man! That is an awesome write up, thanks a bunch for the response! Gonna try to get it done tonight.