Interesting Electrical Characteristic—Windshield Wipers and Side Marker Lights

[Gary747]

This morning I replaced the front fender side marker lights with LED bulbs and new amber lenses. This was very straightforward, no issues.

I performed the bulb "change out" with the parking light switch "on" (to verify electrical continuity to the new bulb before assembly) AND with the ignition key switch in "Accessory" so that the turn signals would be available.

When done, I decided to clean up the dirty ground connections that are in the engine compartment just outboard of the headlights. One of the two wires from each side marker light goes directly to these grounds, one each for the drivers and passenger side.

The right side went exactly as expected. No surprises.

The left (drivers) side though did catch me unaware. When I backed out that grounding screw and "opened" the side marker light ground, the windshield wipers came on in low speed. The wiper controls on the steering column were totally ineffective. I shut the wipers off by turning the key from "Accessory" to "Off".

I cleaned the wire and restored the ground and everything returned to normal.

Just an interesting observation....

 

[Chris]

I wonder if it's supposed to do that. Seems rather odd.

 

[machoheadgames]

This morning I replaced the front fender side marker lights with LED bulbs and new amber lenses. This was very straightforward, no issues.

I performed the bulb "change out" with the parking light switch "on" (to verify electrical continuity to the new bulb before assembly) AND with the ignition key switch in "Accessory" so that the turn signals would be available.

When done, I decided to clean up the dirty ground connections that are in the engine compartment just outboard of the headlights. One of the two wires from each side marker light goes directly to these grounds, one each for the drivers and passenger side.

The right side went exactly as expected. No surprises.

The left (drivers) side though did catch me unaware. When I backed out that grounding screw and "opened" the side marker light ground, the windshield wipers came on in low speed. The wiper controls on the steering column were totally ineffective. I shut the wipers off by turning the key from "Accessory" to "Off".

I cleaned the wire and restored the ground and everything returned to normal.

Just an interesting observation....

I’m a little late here but this isn’t that surprising. The side markers receive power and ground from the front turn signal lamps and they alternate how the ground and power is delivered. So, with parking lamps on as you had it, the side markers would be grounding through the turn signal filament, which carries over to the ground side of the front turn signal bulb, and then grounds through that wire. If it can’t ground through that wire, then that current travels up the turn signal wire and back feeds the Jeep circuitry. Now I couldn’t have told you that it would turn on the wipers, but there are a lot of weird things it could do. I’ve heard of things like that sounding the horn, or that messing with the horn messes with the wipers also. Another funky thing is if you put LED bulbs in the front turn signals, the side marker current can’t get to ground through the turn signal circuit and out the bulb like it could on an incandescent, so instead it back feeds the dash turn signals and turns them on with headlights on. It’s a mess.

In short, nothing is wrong, the side marker grounding is just backfeeding other circuits with that ground wire disconnected. Keep the wire grounded and you shouldn’t ever have any weird behavior like that. And don’t put LEDs in the front turn signal spots either unless you want to rework the side markers with diodes and resistors to make that all work properly.

 

[Gary747]

I’m a little late here but this isn’t that surprising. The side markers receive power and ground from the front turn signal lamps and they alternate how the ground and power is delivered. So, with parking lamps on as you had it, the side markers would be grounding through the turn signal filament, which carries over to the ground side of the front turn signal bulb, and then grounds through that wire. If it can’t ground through that wire, then that current travels up the turn signal wire and back feeds the Jeep circuitry. Now I couldn’t have told you that it would turn on the wipers, but there are a lot of weird things it could do. I’ve heard of things like that sounding the horn, or that messing with the horn messes with the wipers also. Another funky thing is if you put LED bulbs in the front turn signals, the side marker current can’t get to ground through the turn signal circuit and out the bulb like it could on an incandescent, so instead it back feeds the dash turn signals and turns them on with headlights on. It’s a mess.

In short, nothing is wrong, the side marker grounding is just backfeeding other circuits with that ground wire disconnected. Keep the wire grounded and you shouldn’t ever have any weird behavior like that. And don’t put LEDs in the front turn signal spots either unless you want to rework the side markers with diodes and resistors to make that all work properly.

Thank you for this feedback. I have slowly replaced incandescents with LEDs in several places in/on the Jeep, but I have NOT done the turn signals and may not ever. The headlights and interior were greatly improved when I switched to LEDs, but I don't think I NEED that type of improvement with the turn signals.

Unlike my other cars, the YJ does not have an audible warning if you leave your lights on while parked. I have, on three occasions, drove to work in the morning darkness, arriving after the sun has come up, then parked all day with the lights on. I come back to a low or dead battery. My LED conversion has the goal of greatly extending the battery life when the lights are left ON while parked. If I tackle turn signal LED's, it would be for this reason only. OR, I may design an audible warning system to sound if the lights are on and the ignition key is removed (or something like that).