A ground problem is possible but ground problems tend to cause circuits to go open so you get nothing instead of getting something. That said, it's an old bike and time spent servicing the grounds is time well spent so do not regret it.

What you know for sure is power is going someplace it should not be going. I would have to study the wiring diagram at some length to find where those two circuits (tail light and t-sigs) cross paths. So do this. Pay attention to the flasher relay in the circuit diagram.

A short between the two circuits is also likely. So examine the harness under the tank and along the top of the rear fender and look for rubbed spots. It could also be rubbing in the rear tail light shell.

Removing the tail light bulb and seeing what that does to t-sig operation may offer a clue.

If flasher relays were cheap I would say just replace it as a diagnostic. last I looked they are not cheap.

good luck Mr. Phelps.

Out for a ride today and ended up with some kind of electrical issue. Tail light blinks when signal is on And the rear the signal lights blink dimly out of sync with tail light. Trying to isolate problem but electrical is a bit of a mystery to me. Could it be a loose ground somewhere ?

I may need to disagree with Arni. The tail lamp and rear flasher lamps on a '81 RT sit atop a plastic rear fender, so all share a common Return wire. If that "easy" path back to the battery is lost, the the 12V takes the next easiest path back to the battery, which is through the wiring of other interconnected devices. It's a very common issue.

Long-time readers of my posts will already know what the problem is and how to fix it.... One of your Return connectors (98% of the time the issue is inside the CONNECTORS) has lost it's ability to make contact, either inside the tail lamp housing (behind the chrome reflector) or in the rear fender to main harness connector (next to the battery). The brass alloy connector has merely lost electrical contact due to long-term corrosion due to water. So the loss of lighting is not the issue, it's a symptom of the issue. The real issue is corrosion, which causes loss of electrical connectivity.

Now, if/when you find this connector, simply un-plugging and re-plugging the connector is going to fix the issue. But before you pat yourself on the back, remember that corrosion is a chemical problem and this normal physical occurrence is simply going to happen again and again and again and... Well, you get the picture. However, the next time might involve a traffic citation, or worse yet, being struck from behind by a car because they simply couldn't see you.

What I recommend is that you (one at a time) unplug each connector inside the tail lamp, the tail lamp connector next to the battery, and all the bulb bases... and treat them with No-Ox-Id which is s a compound that both stops the corrosion AND promotes good electrical contact. All it takes is about 1 droplet per contact... a VERY small amount. The smallest tube they sell is enough to treat 10 Airheads.

Then, in days to come when you have the fuel tank off, you can treat the prongs of the starter relay and voltage regulator. Follow that with all the connectors inside the headlamp shell. Because the other thing we know is that, if there was enough age and water intrusion to start corrosion on one connector, then the issue exists all over your bike. The only real choice you have is to do the work in the comfort of your shop, or do the work on the side of the road.

Hope this helps.

From another ABC member with similar issues....
( https://www.airheads.org/forum/my-airhead-needs-help/1381-1978-r80-7-goes-dead-when-turn-signal-is-used )

See that green stuff ?

81RTBC,

Since the tail lights and turn signals are interacting, the problem most likely lies in the wiring they share. This would be the ground wiring. The rear frame wiring harness plugs into the main harness through a 6 pin connector: 1 power wire for each light (tail light, brake light, left and right turn signals) and one ground wire for all of them. This connector should be on the left side of the frame just below the rear end of the tank. On my 95RT, the main harness connector is attached to the frame and the rear harness connector plugs into it. Yours should be the same or at least similar. Separate the connector halves and inspect/clean/treat with NO-OX-ID grease. This is Wobbly's most common advice for electrical problems, and he is absolutely correct. Now do the same inspect/clean/grease on the rest of the rear frame harness connections, both the spade connectors and the bulb sockets. Let us know how this works out. In the immortal words of Red Green, "we're all in this together, I'm pulling for you".

Andy
1995 R100RT
ABC# 15601

To be clear, Mr Murphyam and I are in agreement. The electrical function I call "Return" is what he is calling "Ground". They are one and the same function, and on an Airhead involve the electrical power conveyed by the Brown wires.

We must all hang together or we will hang separately.
-- Benjamin Franklin

😉

Yes, 1981 RT

So i pulled each signal light , checked connections everything was spotless, unplugged and plugged wires back in, checked signal same problem, front lights signalling rear taillight blinking signals not working. Replaced signals with Led signal lights i picked up at Lordco ( auto parts );then nothing worked, put the incandescent back in same previous issue , pulled the brake lens off there is already a led panel in there , connections looked fine. Flipped the seat up unplugged 6 connector it was clean and full of what looked like silicone dialectic plugged it back in . Now everything works.
I can’t find that No-Ox- ID anywhere up here so I’ve ordered and should see it in 10- 20 days .

Your actions prove my diagnosis. The corrosion in your case was simply microscopic instead of big green blooms. Which is why it's to your advantage to follow-up and treat the other important connectors on the bike. In your case, you cannot see your enemy, so it's going to be important to be "proactive" in the fight.

The dielectric paste is great as a problem prevention tool. That is, before the connection(s) have issues. It's really good at keeping water (the main cause of the corrosion) out of the connection(s). It will allow a clean connection to persist much longer. However, as its name says, it does not actively promote electrical connection.

The anti-oxidation portion of No-Ox works to eliminate corrosion and promote connectivity, and then also excludes water that might allow it to re-start. So it you're playing "catch-up ball", then the later product is going to be a better choice.

the LED panel in the tail light is quite sensitive, very little current will light it up. If power from the blinker circuit was getting into the power wire to the tail light and then going to ground through the bulbs then the bulbs would light up. that would be a short between power wires. Corrosion does not create short circuits, especially...um...microscopic corrosion..

I predict the issue will return.

After a couple month wait for the No-Ox Id to arrive, I applied it to all light connections and the six way plug under the seat .

Zero problems since .

Thanks again.

@81rtbc My mom and step-dad bought 3 or 4 new BMWs during the late 70's and through the 80's. If you weren't around then it's very hard to imagine what they put these motorcycles through. Those guys would ride rain or shine for hours on end. My parents would read about some rally in Montana and take off from Georgia with 1 day's notice just to get the badge. So most of these bikes have seen immense amounts of water, water that was blown up into all parts of the wiring. It was just what they did.

So you need to know this and let it percolate into your calculations when you run into these electrical issues. These bikes were simply "ridden hard and (literally) put up wet". 40 years on all that water has converted to corrosion on the connectors. You'll hardly ever have a "short circuit" unless the owner did some mods.... which were also highly popular. But most of the time if you don't see modifications, then think "Corrosion !"

Hope this helps.