XJ750P Wiring Question

Hi,
After cleaning up my wiring and repairing all connections back to stock and testing all switches, plug/sockets and lights everything is looking good except...
The problem I'm having doesn't look like a 750P specific question and the part of the wiring that I'm questioning does fall into line with the XJ750 Seca(UK) from the haynes manual.
Now the specific question, sorry for the long-winded intro.
The tail(park) lights don't come on when the headlight is on, dash and license plate lights all function normally though. The actual output for the tail(park) lights comes directly via the 'computer monitor' section and is separate from the dash and license lights also. "see red circuit in attached schematic"

I've only tested this without the engine running (continuity is good from the monitor to the rear lamps) as I haven't actually got the engine running at the moment (carbies and other sundry bits are off). Is this normal, do the tail/park lights only come on with the engine running and the park/head lights on or should they also light up without the engine running?
This is boggling me a bit and the carbie rebuild is a ways off so... Help! and thanks in advance

 

The park/tail lights should come on without the engine running with the ignition turned to P (park) and if I remember correctly there is a fuse inside the headlight bucket just for the tail light.

 

Hi Bushy,
Thanks for that. I just checked the voltage coming out of the 'computer monitor' block and have 3.8v coming out at the first connection which correlates to the voltage at the rear also.
I hooked 12v straight into the lamps after isolating from the 'computer monitor' and the lamps are functioning without a hitch too... maybe I have a fault in the 'computer monitor' after all.
I was hoping that the engine running and the 'computer monitor' kicking in after the tacho starts running (according to the haynes manual) would be where the glitch was.
The bike was running when I got it but because of the state of it, I stripped it down before checking whether these things were running to start with... oops!
Thanks again for the reply.

 

Finally worked out the tail light wiring problem.
The problem was a missing power coupling into the CMS which powers the tail light and has a fuse inline.
The power is able to flow from the park position from the ignition or from the headlights on position into the CMS but neither of these sources will feed each other as they are isolated using diodes. So, the fault lay in the missing fuse, short wire and the lack of power being supplied to the CMS for the tail light... but as the tail light was connected to the CMS it would detect that there was a circuit and the dash warning was off. good times!
The other part of the circuit which supplies the power for the dash lights is before the CMS power input and is not monitored so all of those lights were working... now I'm only explaining this since If any one else ran into this problem they would be happier realising that the tail light only comes on when the engine is running or the ignition is in park. So no tail-light with ignition on and motor not running! 8O
I've edited the original pic to show the missing part of the wiring. Just a fuse and a short length of cable which marries into the park light circuit.

On another note, is there a supplier that is used to supply the correct colour-coded wiring in short lengths (5metres or so)?
I could do with replacing some complete circuits which have been chopped and corroded and joined etc and the original colours would be nice.

 

Well I'm not great on electrickery but ..glad you worked out the silly fuse in headlight thing,my tail light comes on with ignition on without th motor running... or park on th ignition. Mines an 81 yours is 85 and ex cop so maybe one or other is th difference.

 

I'm thinking that there was a bit of, dare i say, jigery pokery with the police wiring since there is no actual light switch and the headlight is ON and thats it.
In its place is the patrol switch and mic switch which are not much use since nothing is connected apart from the pulsing relay, but... I'm sure some cool use will come into play... flicks mic switch for blue LED TRON look whilst cruising down the highway...
But thats just me, thanks for the info again bushy.

 

Oops!
Looks like I did the old 'this is how it is' without paying attention *slaps self*
The statement "So no tail-light with ignition on and motor not running!" from one of my previous posts is just plain wrong.
It should read

"with low battery voltage the tail-light won't light up without the engine running or with no supply line into the CMS for the tail-light it won't light up no matter what"

My bad and since the battery is only just fully charged now, I plead ignorance on the first part of the statement.

 

I have POLICE version wiring diagram in digital format should you require it in future.