3 wiring questions for "81" xj750 rj

I'm doing the final wiring connections on a 750 seca frame-up build. I'm using a salvaged
harness that the seller said was from the same model. everything so far has gone together
with the obvious color connections but there are three exceptions.
#1, The substitute clutch switch I got from Chacal has 2 wires ; brown and green w/yellow.
( substituting a brake switch). The designated clutch switch colors are black w/yellow and
blue w/yellow. Which connects to which ?
#2, The wires leading into the 6 pin diode connector, with the assembly groove on the left,
are white w/blue and blue w/yellow on top. A light blue wire and a white wire feed in on the bottom.
On the diode side of the connector there are three wires on top ; black w/red, white, green.
on the bottom are ; blue w/white and white w/green.
The diagram for the xj750rh in the haynes book shows the same 4 colors going into the connector,
and out of the connector to the diode. Do I need to trash the existing diode and get one with the
colors the same into the connector and from the connector to the diode ?
#3 Next, I'm wiring up the starter relay. The red positive battery connection, the heavy black wire to the starter
and the red wire to the main switch are obvious. two wires are hard wired into the solenoid and bundled together ; a black wire and a yellow w/red. they each have a single female push connector on the end.
Close by is a 2 pin connector with a blue w/white wire and a red w/white feeding it. Should the two wires
hard wired to the solenoid be connected to this ? which to which ? Also, a loose wire is coming off the same
nut as the positive strap. The only wire left coming off the harness is a white w/red should the loose wire off the hot nut be connected to that white w/red ?

 

1. It's a switch, so it does not matter
2. The diode block is used on multiple platforms, the wire colors will not match on the XJ750R
3. Should be R/W to R/W and L/W to L/W with matching two pin connectors. Do you have and aftermarket starter solenoid?
It really won't matter as solenoids are not polarity sensitive.
The W/R wire is the battery sensor for the CMS "Batt" warning. If you have a wet cell battery it would connect to the sensor installed in the battery. If not, you can add a resistor that will act as a voltage monitor.

Probably a typo but that should be main fuse

 

Yes you are correct, that red wire should go through the main fuse befor the switch

 

Thanks rooster I wired the thing up but the electrical system still has bugs.

 

I got my "81" xj750 project wiring assembled. The bike starts right up " Hooray"
but aside from ignition nothing else seems to be working. I don't remember if I
grounded the harness or not. Where would be the best location to test if the black
common ground wire is connected to the frame ? Where is the harness usually
grounded ?

 

The XJ750 Seca (at least the 82) has two eyelet terminals to provide ground for the main harness and associated circuits. They are located at the right coil mounting hardware under the tank. On the 82, the TCI and tail light share the same terminal, so the tail light should be working if you have ignition. Are you sure the Head and Signal fuses are present and not blown?

 

all the fuses are ok. I switched to an aftermarket blade fuse block because the one attached to the harness
was missing parts. but I copied the connections that were on the previous fuse block. The ground connection
at the right coil could be better since There was new paint there, I can improve that. I'll see if the black wire
at the TCI is grounded. Could the diode be involved ? It has to be something common to the whole electric system
with the exception of the ignition.

 

Just checking to be sure that you did not use a common-ground fuse block.

 

Verify the wiring by pulling the head, ignition, and signal fuse. Turn the key on and the input side of the fuse block should have 12v at the input of each respective fuse. Install the fuses and check the output side just to be sure all is well.

Yes, make sure there is bare metal at the frame where the ignition coil core contacts the frame and the eyelet terminals (Qty 2) attach.

Every black wire should have continuity to ground (frame and motor) and back to battery negative. The 750 Seca typically does not have the extra ground wire from the engine to frame and relies on the motor mounts to return to battery negative. I suppose powder coating or other paint could possibly be an issue here??

The diode block for the 750 Seca performs two functions. One is to rectify AC signal from the AC Generator and apply DC to the headlight relay to engage the relay when the motor spins up.
The other diode is part of the ignition safety circuit and allows the side stand relay to engage in neutral when the side stand is down.

 

I used an aftermarket low profile blade fuseblock It had accomodation for 5 fuses ,I used 4. As far as I could see it's not grounded.
I matched all the wire colors and connections to the old damaged glass fuse block.

 

Common-feed I meant.

Like this


which will not work without a rewire of the bike.

It sounds like you did use this type:

 

Yes that's the one I got from autozone

 

Yes you are correct I looked and the taillight does come on, but I have no function from the handlebar controls, the head/fog lights,horn and
instrument cluster.

 

Did you do this?

And this

And this

 

The Seca 750 does have a ground cable from the frame to the engine (at least those built from late '81 (early '82 model year) and on do), but it's sort of hidden. It runs from the rear of the engine case (next to the negative battery cable) under the secuity chain box, and mounts to the frame at either the security chain case mounting screw, or the lower airbox mounting screw.
The engine mounts do provide ground, but I think Yamaha ran the strap as insurance against corrosion since cleaning the engine mounts is a fairly big chore should they become corroded.

 

I have mine took a part right now I can look

 

Well, the extra ground would certainly not cause a problem and could add some insurance if a poor engine to frame ground occurred. However, I don't see where Yamaha included the extra ground strap on the 750 Seca's. Not to say they don't exist on some of them as manufacture's don't always build per print.

It appears the 650 Seca is the only one (per print) in the XJ series to include the ground strap in conjunction with a solid engine mount.

 

I did a voltage test today, using the key switch and the fuse block, I would appreciate any analysis of these results.
A- key off, fuses pulled, hot side checked - headlight- 0 volts, main - 13.08 volts, signal/horn - 0 volts, ignition 0 volts.
B- key on, fuses pulled, hot side checked - headlight- 0 volts, main - 13.08 volts, signal/horn - 0 volts, ignition 0 volts.
C- key on, fuses installed, hot side checked - headlight- 0.20-0.39 volts, main- 12.50-13.00 volts, signal/horn- 12.20 volts, ignition- 12.20 volts.
D- engine running estimated 2000 rpm + -, hot side checked - headlight- 0.20 volts, main- 14.50 volts, signal/horn- 14.33 volts, ignition- 14.33 volts.
Also the engine did not cut out when the kickstand was lowered. The engine started without being in neutral or the clutch lever pulled
and I installed the engine into a heavily painted frame and neglected to install a ground strap between the engine and the frame.
I will do that tomorrow and see if it helps. Any interpretation of the voltage results in the tests would clue me in to what to check next.

 

From this I would suspect you have not identified the fuses properly, and actually the Signal fuse has no voltage. If the signal fuse is missing or blown the safety circuit will be disabled. You should see a very faint glow in the neutral light that will brighten just a bit if you enable the flashers either left or right.

It certainly won't hurt to add the ground strap between the engine and frame. I suspect Yamaha masked some of the painted mounting points at the initial build to ensure a good frame to engine ground.

After verifying the main fuse is OK with 12V on input and output power up with just that fuse installed. The hot side of the fuse box (front of bike normally) should have 12V for each or the 3 fuses with the key on. This ensures you have the fuse box wired correctly. Here is how the stock fuse box connects with wire colors. Note I had to guess at the wire gauge so that may not be accurate.

 

thank you I will check continuity to all these locations with my multimeter

 

^^??

I know you asked about the diode block in another post. As stated earlier:

Here is how the colors match up. Note the Seca only uses D1 and D2, and since you mentioned Len had sold you a slightly different one I suspect (knowing Len's thoroughness) that it contained the correct diodes to do the job. That said, my original and replacement are wired as below:



D1 is for the safety circuit, and D2 is for the headlight. R1 and D3 are not used on the XJ750 Seca and there is no mating wire on the main harness for the B/R wire.

Given the voltages you posted earlier on the fuse box I would direct my attention there

 

Thanks Rooster, Using the wiring diagram in the haynes manual, I did continuity tests on all the wiring and discovered that the brown
wire at the headlight feed was mixed up with the out put wire on the signal fuse, when I switched them the horn worked, the signals flashed,
and the instrument panel lit up and functioned properly. I also, just to make sure, swapped out the diode and the headlight relay with ones I
bought on ebay. The only system not functioning now is the head and fog lights. The headlight wires from the fuse block through the relay
to the dimmer switch test out continuous as do the wires through the kill switch and the fog light on/off switch. From there the wires go through
the atari control module and from there to the three wires that power the headlight. I tested the headlight and fog lights with an emergency starter battery
and both lights were good. Now I need to test the circuits between the handle bar controls their connectors and the atari display panel. I will test all the
switches for function again, butnext I'll have to check out the wiring in the display/control panel. Is there a wiring diagram for the inside of the Atari ?
The Haynes manual doesn't provide one.

 

So did you solve this issue with no voltage on the headlight fuse? You are gonna need that 12V for the headlight circuit to work.

As with most electronics the drawings were never released likely based on intellectual property and not wanting to share with their competitors. That said, the headlight circuit within the Atari routes through reed relays, so you should have a direct short from the low/high beam input to the respective low/high beam output.

Do the simple test (if you have 12V at the head fuse) and short the R/Y to L/B at the headlight relay socket. That will let you know if the wiring / switches / Atari are functioning or if you have an issue with the headlight relay control; diode block / AC Generator or associated wiring not energizing the relay at start up.

 

Thanks Rooster, I did that test, swapped out a faulty headlight relay and the lights work fine now. By the way, I have two
heavy red wires in the headlight bucket that don't connect to anything and are capped off with crimp fittings. Are they provided
for future electric accessories ?

 

I don't think those would be part of the stock harness. Perhaps someone added them along the way to improve the headlight intensity or some other accessory.