TJ: No turn signals with Headlights on...

[Mike]

Well, I always seem to get the weird :poop: wrong with my Jeep. This time, the turn signals will not blink when the headlights are on. Since they say that it takes a a village to raise a child (or an idiot, in my case), this Village Idiot is turning to the MJR village for help.

I recently changed the standard tail lights out for LEDs. I have had LEDs for turn signals in the front for years. I have already modified the flasher to not blink fast.

The symptoms:

• All functions of the turn signals and the hazards work perfectly as long as the headlights are off.
• When the headlights are on, the brake lights, running lights, back-up lights all function as expected. The Hazards and the turn signals do not work.
• If the turn signals or hazards are on and then the headlights are turned on, the lights stop blinking. They will resume blinking when the headlights are turned off.
• All functions worked as expected before the LEDs were installed.

What has been tried so far:

• I moved the ground connections for the tail lights from the tub to the frame = no change.
• I switched the (modified) stock flasher to an EP26 flasher for LEDs = The lights blink fast and the turn signals still do not work with the headlights on.
• I measured the volts at the tail lights under various conditions and got the following results:
  • Power on, no signals going to the lights = 1.5 volts
  • Turn signal on, headlights off = 12 volts when blinking
  • Headlights on, no signal = 6.1 volts
  • Headlights on, turn signal on (no blinking) = 8.5 volts
  
  
• I measured the resistance across the pin positions at the flasher connection and got readings between .57 and .21 M Ohms depending on the two pins tested. Unfortunately, I don't know what the proper resistance should be, so I don't know if these measurements are significant.
• I have read through Stu Olsen's troubleshooting guide several times, and I am still at a loss. Guide can be read at this link: http://www.stu-offroad.com/electrical/led1/led-5.htm

I'm looking for new ideas. Any advice would be appreciated. :dunno:

[6spdYJ]

Had a buddy with a postal LJ with a similar issue. He had it diagnosed to a "multi-function switch". Wish I could offer more.

[Russ Chung]

[*]I measured the volts at the tail lights under various conditions and got the following results:

• Power on, no signals going to the lights = 1.5 volts
• Turn signal on, headlights off = 12 volts when blinking
• Headlights on, no signal = 6.1 volts
• Headlights on, turn signal on (no blinking) = 8.5 volts

Mike,

A stock '99 TJ has three wires going to the rear lamp assemblies:

• Left: pin 1-backup vt/bk, pin 2-stop&turn signal dg/rd, pin 3-tail light bk/yl
• Right: pin 1-backup vt/bk, pin 2-stop&turn signal br/rd, pin 3-tail light bk/yl
• The lamp sockets are grounded to the lamp assembly

I don't think the rear LED tail lights are hooked up properly. I would expect to see either 12 volts or zero volts but nothing in between:

• Power on, no signals going to the lights, pin 2 = 0 volts, pin 3 = 0 volts
• Turn signal on, headlights off, pin 2 = 12 volts when blinking, pin 3 = 0 volts
• Headlights on, no signal, pin 2 = 0 volts, pin 3 = 12 volts
• Headlights on, turn signal on, pin 2 = 12 volts when blinking, pin 3 = 12 volts

How many wires on the LED assembly? three wires (backup, stop&turn signal, tail light)? or a fourth wire for ground?

Russ

[aw12345]

Sounds like you need to review how you wired your tail lights. You should have 12 volts from the flasher and brake lights and 12 volts from the tail light wire

[Mike]

Okay, did some more tests:

Wires seem to be connected properly. The LEDs have a "high" wire (Brake/Turn) and a "low" wire (tail lights) according to the wiring plan that came with the lights and a ground wire. These match to the wiring that I need.

I kept the stock plastic connector for the wiring harness so that I could change out lights and troubleshoot easier. So, I disconnected both tail lights and tested the voltage at the connector so that no interference from the new wiring should apply. I got the following volts:
Back up = 12.4 v
Turn signal = 12 v when powered/blinking
Tail light with turn signal on = 8 volts.

Something that I didn't notice/test originally: The front turn signals stop blinking when the lights are turned on. I didn't change any wiring anywhere else in the circuit. Therefore, I think that I can eliminate the new wiring as the cause of the problem.

Looks like Ted may be on to something with his suggestion. Sounds like it is time to swap out the Multi-function switch.

[RAT]

Hey Mike, on my MF switch is the flasher unit. Is that where yours is?

[Mike]

Hey Mike, on my MF switch is the flasher unit. Is that where yours is?

No. Mine is mounted under the column.

Well, $45 later and a new turn signal switch and the problem is still the same. I am still getting 8 volts when the turn signal and the headlights are on. Like I said, I always get the weird :poop:!

I am going to test the headlight switch next. Wish me luck.

[Mike]

Headlight switch is a bit of a mystery to me. With the switch removed, I got 12 volts at two pins and 1.3 volts at two pins and nothing at the rest. There are 9 pins/wires on my headlight switch.

When the switch is in place, I get 12 volts at one more wire, but the rest are the same. In testing each wire, either they had 12 volts, 1.3 volts, or no volts consistently, with one exception.

One wire had 13 volts with the power on and started bouncing all over the place when the turn signal was turned on. But with the turn signal and the headlights on, it stayed constant at 11.8 volts. I don't know if that is an issue, but I sort of doubt it. I'm not seeing anything obvious that makes me think that the headlight switch is bad. A new switch is $31 so I don't want to just go swap it out if I don't think it is the problem.

What could drop the voltage from the battery to the tail lights be sides the turn switch or the headlight switch?

[Mike]

Okay, I might be on to something, but I'm not sure what it means. At the flasher, I am getting 31.5 volts at the hot side. I'm getting this with the power off or the power on. I get this whether the turn signal is on or off. Why would the volts to the flasher be so high?

[1 Bad F N Z]

Okay, I might be on to something, but I'm not sure what it means. At the flasher, I am getting 31.5 volts at the hot side. I'm getting this with the power off or the power on. I get this whether the turn signal is on or off. Why would the volts to the flasher be so high?

I'm trying to get a hold of my son-in-law, he's pretty good when it comes to electrical, Kevin.

[1 Bad F N Z]

Talked with Billy and thought it might be the turn signal switch. Saw that you had replace it. I'd start with the basics and test all your grounds for good connections. Most electrical problems are cause by a bad ground. I'm still trying to get my head around 31.5 volts from a 12 volt battery. Wish I was there to help. May not be of much use, but you'd have a shoulder to cry on, Kevin.

[aw12345]

It started happening after you wired the led tail lights, seems to me you got the wires crossed the turn signals are using the tail light wire for it's ground path. Or atleast that is what I suspect and it's about the only thing that makes any logical sense, unless you did a lot more monkeying around that you are not telling us

[6spdYJ]

Volts equals difference of potential. When you get into the milliamp world of LED's you can see a lot of weird numbers. Try disconnecting the turn signals (front and rear) at their sockets. If the problem is gone when they're disconnected - which it should be - plug them in one at a time and do the same function testing you've been doing. If the problem comes back when you plug one in, check the wiring on that one. If it looks good, swap it for the one on the other side. If the problem moves to the other side you may have a damaged LED causing your voltage goofiness. Remember, LED's are a type of semi-conductor so the voltages you see on them may or may not be referencing input voltage to chassis ground.

[Mike]

Good advice all around. Thanks. Still have the issue, but Kurt and I worked through several tests over the phone last night and found some interesting things.

The 31 volts at the flasher is still there when all new wiring is disconnected. So the problem is not related to the new LEDs.
The 31 volts is on the GROUND wire! That can't be good. It shows the voltage when checked against a tub ground or a chassis ground.
There is no continuity when checked with the battery connected, but disconnected the flasher ground has a good connectivity.

Looks like something that shares the ground has a short.

I have a bunch of things that I have added that run off of the battery. Looks like I will be disconnecting each of them one at a time until I find the source. At least it is Saturday and I have the time....

[aw12345]

Why don't you disconnect the tail lights completely and see if the turn signals work again with the headlights on