Landing lights on, GTN650 transmits...???

[Sig600]

Like the title says, with the landing lights on, the GTN 650 "tx" come on and you can hear the side tone. Only thing we can think of is a wiring shielding problem, but would that key the mike??? Not using a VPX or anything like that, traditional c/b's.

Totally stumped.

[ColoRv]

What kind if lights? Antennas on the belly?

I had duckworks HID's, which caused all sorts of mayhem with my radios. Switched to Rigid LEDs and the problems are gone.

[FORANE]

Start disconnecting the positive wire after the switch going to the lights. See if you can replicate or eliminate the problem with the wire disconnected at the switch, at the light, etc. That will eliminate the wiring as the issue.

[Sig600]

Originally Posted by FORANE

Start disconnecting the positive wire after the switch going to the lights. See if you can replicate or eliminate the problem with the wire disconnected at the switch, at the light, etc. That will eliminate the wiring as the issue.

I don't follow, disconnect the positive wire from the switch, for the landing lights? See if it still causes the problem?

[FORANE]

Originally Posted by Sig600

I don't follow, disconnect the positive wire from the switch, for the landing lights? See if it still causes the problem?

Yes, I would disconnect the positive wire leaving the switch to the landing lights. Then, turn the switch on and see if the GTN650 problem persists. It likely will not. If it does not persist, you have eliminated everything to and including the light switch.
Then, disconnect the power wire as it connects at the landing lights. If the problem persists with lights disconnected, it is not the lights but rather the wiring between switch and light(s).

[digidocs]

Is the landing light grounded through the airframe in the wing?

If so, I suspect that the return current through the airframe is creating the issue.

As a test, try isolating the light from the airframe and running a temporary ground wire back to your ground block. If that fixes it, you can either run a permanent wire and declare victory or spend some time understanding where the airframe ground current is creating an issue with your GTN650/audio wiring.

Hope that helps,
David

[Sig600]

Thanks guys, electrical stuff is far and away my weak point.

[Mike S]

Transmit is usually triggered by grounding a trigger wire in the radio------in avionics speak they say taking it to "Low".

Where are you running the ground side of the PTT switch?? I like to attach this wire straight to its own ground.

From what you describe it sounds like the light circuit is causing a physical short to ground in the radio, or through some weird electronic coupling (inductance??) making the radio think it is seeing a low on the PTT.

Are you by any chance running a hot lead to the lights, and switching the ground side of the circuit----------are you running dual purpose lights, that double as wig-wags?? are you running the lights straight off the switch, or is there a relay in there??? Does any other electrical gremlin raise its head when you switch on the lights?? Does the radio xmit work normally with the lights off? Answers to the above will help with a diagnosis.