Tail Lamp Warning - Last Gremlin.........

1981 XJ750 SECA

Finally, the bike is finished and has actually been ridden briefly. Love the shaft drive, and, 65mph in 2nd gear with engine to spare has gained my attention and respect.

I am down to my last little gremlin - the Tail Lamp indicator on the computer.

Both tail lights and brake lights work fine, as does the license plate lamp.
And it seems that all of the circuitry, based upon the schematics, is routed through the computer. Which is where the question comes in.

If the lamps are all working fine, and the circuits all run through the computer, then why would the computer still throw a warning??

And yes - not wanting to get into the debates - I did the battery sensor bypass - and no, I won't say what side of the fence I took - LOL

Thank you in advance.

Stephen

 

Hi Stephen,
I had the same sort of issue when I originally did a wiring cleanup.

When I originally got my bike the CMS showed the TAIL warning on also although the tail light was working.

At first the tail light was working but after I stripped the whole bike apart and followed the schematic and patched the wiring back to original the tail lights stopped working!

It turned out the PO had wired the tail lights directly to the ignition circuit and after I cleaned everything up it was one of the bits of wire I pulled out as it wasn't in the schematic.

Anyway here is the post that I did about it.

Turned out I was missing a specific supply into the CMS for the TAIL circuit... It was in the schematic but not actually present in the harness, so something I overlooked when I was cleaning up. It is also something that can be removed easily(bullet terminals and a fuse)and just forgotten.

Hope that helps... as you can see it was a 2 part fault that I had, that probably stemmed from a blown fuse in the TAIL supply to the CMS.

 

If the connections are not extremely clean, they will introduce enough resistance that the computer will "think" one or both of the bulbs is blown.

Clean up those bulb sockets and see if the warning will go away.

 

Thank You!!!!!

I figured that was the first task at hand.

Back to the drawings for sure.

Stephen

 

Does the warning come on immediately when the computer initializes, or does it come up a few seconds later? If immediately, then it's complaining about the tail lights, if later, then it's the brake lights.

The computer has resistors in it that run is series with the tail and brake filaments so that it can check how much current is being drawn. It's pretty picky. I haven't seen bad connections cause it to trip without a visible effect on the lamps, but if the wrong lamps are in there, it may not see as much current as it expects.

My first check would be to make sure there are 1157 bulbs in there.

I wrote up some more detail about the internals of the computer and these circuits here: http://www.xjbikes.com/Forums/viewtopic ... art=0.html

 

Wonderful - Thank You!!!!
Once I finish with the Wood Pile, I will jump into this.
Under the gun for time since driveway is getting re-paved on Monday.

 

D A M N ! ! ! ! ! !

Replaced the bulbs with new 1157's
pulled apart and cleaned all the connectors (as best I could)
Still get the warning.

It happens during the first initial scan, which lends itself to the taillight circuit.

Stephen

 

OK. So, assuming that both bulbs are lighting, you're probably going to need to trace the supply to the tail lamp to ensure that the wiring has not been modified.

I'm not sure which wire feeds the tail filaments, versus the brake filaments, but I think it's the Blue/White. In the headlight bucket, there is a 9-pin connector, with 8 pins populated. If you disconnect this one, you will disconnect the Blue/White wire (among other things), and the tail lights should not light when you turn the key. If they still do, then either I'm wrong about the Blue/White, and it's really the Yellow/White, or the tail lamp wiring has been bypassed somewhere.

The reason I think it's the Blue/White, is that the other choice is Yellow/White, and Yellow is what's used for the brake switch signal.