Rear Brake Light

I have some new LED signals that I am installing on my 1982 XJ750R Seca. The lights have red and yellow leds so that I can use them as auxiliary brake lights as well as amber signals. My problem is I have my bike so disassembled right now that I don't know which one of the wires to the taillight assembly is the tail light and which comes on for a brake light. Is the brake light the blue/white wire or the yellow one?
My wiring diagram is so small I can't tell where either end up. It looks like both wires terminate ate the gauge assembly.

 

I've got some diagrams that might be helpful to you. This is an excerpt from teh XJ 750 RH RJ and RK models diagram.

 

That is much easier to see than my diagram. Thank you. I still can't tell from that which wire is the one that is always on when the bike is running, and which one is the "brake" light indicator positive wire. Is there something in the diagram I am missing?

 

Hmm, guess I didn't go back far enough. I'll look it over real quick.

 

Both wires in the diagram go back to the computer thing and don't indicate what their functions is. So you'll just have to hook them up and see which one gets powered only when you're actuating the brakes.

 

Might I suggest a voltmeter? If you turn the key and it gets 12V, it'll work. If you get no volts, press the brake pedal. If you get 12V, that's the other brake light lead. If you still get no volts, try the flashers. If you STILL get no volts, it's a ground (and likely a black wire in the first place).

There should be at least two leads that always have 12V: one for the brake light and one for the license plate light. It's also possible - though not likely - that your bike has running lights in the flashers. Those will also have 12V all the time.

The only reason you might care about one 12V lead vs. another is that some of them are fused (flashers) separately. A continuity tester (ohmmeter) and a good wiring diagram will help you sort that out.

Multimeters are cheap. Get one.

 

SHoudln't the brake light lead be hot only when a brake handle or pedal is actuated and the 12v lead for the tail lamp and license plate lamp always be hot with the key on?

 

Tail light and brake light are the same bulb, so I tend to call them both "brake light". But yes, you are correct.

 

YELLOW is the brake light wire.

BLUE is the running lights/license plate light wire.

It's the same on almost all XJ models from this era.

and yes, the above statement = TRUE.


And don't forget that if you use the LED bulbs in the turn signals (flashers), that the stock flasher relay WON'T flash them, you'll have to go to an aftermarket electronic flasher unit, and in doing so, the self-cancelling feature of the stock flasher system will cease to function.....

 

You should be able to just add a loading resistor with the proper rating in parallel to the LED array to drop the resistance enough to allow the flasher to heat up and start flashing.

 

That's true, also........but adding a resistor kinda defeats one of the main benefits of usings LEDs (lower current draw).

 

didn't think of that aspect. In the auto world I'm coming from we use them for the faster "on" time. Amazingly that half second quicker turn on that LED's have let's drivers respond quicker than traditional "heat to a glow" bulbs.

 

Yes, that quicker response time is real and important. Life is so full of tradeoffs...........