Hey all, I brought home a nice running RT3 Monday with one major issue, not tail light.  The head light is working just fine, horn works (no signals on the bike as of yet) but tail/brake light is not working.  I'm not great with electrical at all so if anyone has any suggestions on a starting point I'd appreciate it.  I have thought of just getting a whole new main wire harness but funds being what they are I'd really like to see if I can fix this and well learn something in the process. 

First thing to check is the bulb of course

Thanks Mark, I guess I should have mentioned that I did check the bulb.

I'd better start by saying wild guessing to a point by me so see what the knowledgable say.
I couldn't find an RT3 diagram but see the link below to consider.
First check if the wires where the tail & brake light plug in are live. Brake light will only be live at the bulb when the pedal or lever are operated.
Brake & tail light are two seperate circuits.
If your tail is magneto powered & only operates when motor runs then i think this color diagram might still be relative in "73 & tail would be dark blue like the intruments.
Stop light i think should be yellow or yellow-green.
On the other hand if tail is battery operated then all bets are off but light brown should be involved somewhere as is DC live after the main switch.

www.yamaha-enduros.com/index.php/wiring-...rt1-b-wiring-diagram

Tail and stop both run off battery on that model. 

So do signals and horn...  you don't have signals but you said you have a working horn?  Does horn work only with key on?  (it should only work with key on...  but since it's the only battery powered accessory that works, prudent to ask as someone could have wired around the key)

Tail and brake circuits are pretty separate...  tail has a blue wire off the key for power and brake gets power from the same brown off the key that powers horn. 

I would check and see if power is getting to the taillight by checking the wires right at where the taillight plugs in.  If you have power, then maybe the light fixture is broken or not grounded. 

 

I'll tread carefuly & ask Mark?--would a battery powered tail light still be blue like a magneto powered one?.
I thought might be a different color, but we never had that in NZ so i'm lost.
Be good to see the correct US diagram for AirborneSilva to study.
I'd better keep out of it so as not to confuse.
Check where the bulb terminals meet at the bakerlite fitting in the bulb socket.
Have seen that break & collapse so not touching the bulb.
Plus check the earth which somehow attaches to the ouside of the socket i think.
Just seems odd that nether are operating.

RT325, going by memory, yes, same blue to tail.  Connects to battery power (red) when key is in headlight on position.

The other "blue" with AC power that powers the headlight from the key switch on that era US model was changed to blue/white and connects to the yellow (AC) wire from the stator with key in headlight on position

Basically the later US spec key switch is a little more complicated so that tail can run from battery and not engine.

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(Early US models were like yours...  yellow from stator goes to blue out of key switch and that blue powers both head and tail lights...  head and tail only worked with engine running)

Cheers for that Mark.

Thanks guys, I did figure out that I have power all the way up to my tail light, so I'm guessing my tail light is bad?

If the bulb is good, and you have power to the bulb holder, then I guess all it could be is the bulb not making good contacts with the holder?