strange electrical problem with turn signals

You have either a broken lamp or a defective ground. If you live in the snow belt, you should check the ground while you have the lamps out to be replaced.

These lamps have two filiments, one for running lights and one for turn indications. Your problem is that a filiment is broken, and when the lights are OFF, the turn lamps get a ground path through the lighting circuit. When the lights are ON, there is no ground path on the same wire, so the turn indicators do not work.

How did you check the integrity of the lamps?

Most strange or weird turn signal, brake or stop light problems I have experienced have been due to a bad ground connection. One problem was due to somebody using the wrong bulb as a replacement.

HI Jeff, Thanks for the info. The turn signal is a single filiment bulb (front and rear). The tail light and stop light are double filiment bulbs. We only checked the integrity of the lamps by swaping some of them. Single filiment to single and double to double. All the lamps light up indicating that the filiments are all good. Thats why I was wondering if the intergration module located in the fuse box could be the problem. This is also where the flasher is located. Hope not as it is expensive. In addition, when the head lights are on and the emergency flashers are turned on the right front and rear turn signal lights stay on and the left front and rear signal lights go out.

Thanks for your comments everything helps.

I would concentrate my search on lights that share the same bulb for marker lights and turn lights. This will focus your efforts on the front.

The turn lights are getting ground source through the filiment of the marker lamps. When the markers lamps come on, the ground for the turn lamps goes away so they do not work.

Let's clarify a couple of things.

The brake lights work fine. The rear running/marker lights work properly. The FRONT turn lamps and marker lamps are the same bulb with a dual filiment.

My recollection is that the REAR has a brake/marker lamp that is the same dual-filiment, and a separate turn signal lamp. The FRONT uses a dual-filiment bulb, where one filiment is the running lamp and the other is the turn indicator. THIS IS WHERE YOUR PROBLEM IS. I'm thinking that you have a single filiment bulb in a dual filiment socket. I'm trying to recall the lighting on my daughter's Tacoma, and I might have recalled incorrectly. But, I think you have a single corner marker on the front of your truck, and this lamp provides marker lamp and turn signal duties. If so, it MUST be a dual filiment type bulb.

Hi Jeff, Again thank you for your input. You are correct the brake lights work fine and the rear running marker light works properly, although the right one seems a little dimmer than the left one.

The front turn signal light and the,marker lights are seperate units with seperate bulbs.

We will spend some time investigating the front turn signal sockets and wiring. Your logic is sound and suggestions are an excellent place to look. If you have additional ideas please let us know. We will let you know if we find the problem.

Thanks again for your assistance.

Kind regards, Les