Really weird headlight/turn signal problem

[MSHappyCampers]

When my headlights are on the left turn signal does not work! When I pull the headlight switch on, the left turn signal indicator on the dash display lights up about half brightness, and when I turn on the left turn signal it shows a weak flash on the dash but doesn't flash the outside turn signal lights! The turn signal works fine with the headlights off.

I didn't know there was any kind of connection between the headlights and the turn signal. Can anyone point me in the right direction to finding this problem?

I really appreciate your input!

[twinboat]

Signal and tail lights often share a bulb with 2 filaments.

Start by checking them..

[BCarp]

It sounds like a low voltage problem. Do you know what chassis you have? I see it's a DP, but I don't know much about Monaco.

I would try to measure voltage going to the turn signal switch with headlights on and with headlights off. You could have a bad connection.

Note that some chassis will blink the ground wire to the turn signals instead of the 12v line. That type of chassis will keep the 12v on constant when the side markers are on.

Hopefully someone with your chassis has a wiring diagram.

Good luck!
--Brian

[Ljwt330]

You've heard it many times before, "check the grounds." Twinboat has you on the right track, IMO regarding the double filaments in the tail/brake lights as the first place to look.

[MSHappyCampers]

Originally Posted by twinboat

Signal and tail lights often share a bulb with 2 filaments.

Start by checking them..

Guess I'm missing something here. It seems to me that the only thing that could happen would be one filament burns out, but if it were that then they wouldn't work with the headlight off.

[MSHappyCampers]

Originally Posted by BCarp

It sounds like a low voltage problem. Do you know what chassis you have? I see it's a DP, but I don't know much about Monaco.

I would try to measure voltage going to the turn signal switch with headlights on and with headlights off. You could have a bad connection.

Note that some chassis will blink the ground wire to the turn signals instead of the 12v line. That type of chassis will keep the 12v on constant when the side markers are on.

Hopefully someone with your chassis has a wiring diagram.

Good luck!
--Brian

Brian, wouldn't that affect the right turn signal also?

[BCarp]

I missed that you said left only. It's probably not at the switch then. Check ground and 12v connections after the switch. With the headlights on, there's more current draw, so more voltage drop over wires used by the both the headlight and turn signal circuit.

Are your front and rear turn signals both not working? Do you have separate side markers and tail lights, or are they combined with the turn signals?

[MSHappyCampers]

Originally Posted by BCarp

I missed that you said left only. It's probably not at the switch then. Check ground and 12v connections after the switch. With the headlights on, there's more current draw, so more voltage drop over wires used by the both the headlight and turn signal circuit.

Are your front and rear turn signals both not working? Do you have separate side markers and tail lights, or are they combined with the turn signals?

Neither front or rear work on the left side. There are no side markers.

[Ljwt330]

Your symptoms are consistent with an electrical feedback through the left turn signal circuit. These types of problems often happen due to poor grounding of one circuit leading the current to seek a ground through an adjoining circuit.


If your tail light and brake light share a double filament bulb, they share the same socket and that socket shares a common ground. If that ground is bad, tail light current will flow into the flasher circuit to ground itself via the front bulbs and dash bulb ground.


I'm not saying this is your problem as I don't know if you have double filament bulbs. However, the concept is correct and your symptoms are consistent. This would be my first area of search if this was my issue. Regardless, you are getting a feedback through your left flasher circuit. The difficulty will be to find from where that feedback originates.

[MSHappyCampers]

Originally Posted by Ljwt330

Your symptoms are consistent with an electrical feedback through the left turn signal circuit. These types of problems often happen due to poor grounding of one circuit leading the current to seek a ground through an adjoining circuit.


If your tail light and brake light share a double filament bulb, they share the same socket and that socket shares a common ground. If that ground is bad, tail light current will flow into the flasher circuit to ground itself via the front bulbs and dash bulb ground.


I'm not saying this is your problem as I don't know if you have double filament bulbs. However, the concept is correct and your symptoms are consistent. This would be my first area of search if this was my issue.

Thanks Larry! It's raining here right now but I will check that later!

[Ljwt330]

Originally Posted by MSHappyCampers

Thanks Larry! It's raining here right now but I will check that later!

Good luck, and I know you'll keep us updated. Electrical issues like yours are a real PITA so you've got all of our sympathies.

[Alpine36]

Bad ground x3. Give everything the wiggle jiggle test. Good luck.

[sandwip]

when checking any double filament bulb sockets, look inside for a short between the terminals. If you can unplug that socket it is a quick check. I had the same symptoms and it took a long time to find the shorted wires in a push in bulb socket. Going around with a good bulb will eliminate shorts in bulbs. Good luck.

[MSHappyCampers]

Originally Posted by Ljwt330

Your symptoms are consistent with an electrical feedback through the left turn signal circuit. These types of problems often happen due to poor grounding of one circuit leading the current to seek a ground through an adjoining circuit.


If your tail light and brake light share a double filament bulb, they share the same socket and that socket shares a common ground. If that ground is bad, tail light current will flow into the flasher circuit to ground itself via the front bulbs and dash bulb ground.


I'm not saying this is your problem as I don't know if you have double filament bulbs. However, the concept is correct and your symptoms are consistent. This would be my first area of search if this was my issue. Regardless, you are getting a feedback through your left flasher circuit. The difficulty will be to find from where that feedback originates.

Well, I wouldn't get that lucky! The turn signal is a separate bulb behind an amber lens and the tail light is at the top behind a red lens.