corolla 2000 turn signal to trailer

So this is the problem. Got a new trailer, installed a 4-way wire converter wired up so that we can tow the new trailer. But, most of the time the turn signals/hazards don't work on the trailer. They light up on the car, but not the trailer. Troubleshooted over a number of days and found nothing. This is what I did: 1st I checked the voltage for each signal light when it clicked on or off from the relay and the result was a random inconsistent fluctuating voltage ie. 1v 3v 7v 6v 0.1v 8v 2v 9v etc. etc. That first thing does not look right. I believe it should be about 12v 0v 12v 0v etc. etc. 2nd I hooked the trailer to another vehicle, and the trailer's signals & hazards work! So ruled out the trailer. 3rd Disconnected the alarm system to see if that helps. No results. 4th I try cleaning out all pins for the fuses & relay. Still no go. 5th I open the relay and see if cleaning out will work, and still no go. 6th I replace the relay with a brand new (heavy duty) relay for the car! And still same problem! 7th Also tested someone's trailer on their car and it works there, then on my car and same problem. 8th Check voltage near relay area under the dash at driver's side, and same inconsistent voltage that fluctuates all over the place. Another thing I did was change the entire 4-way wire converter to another new one and still same problem! It defiantly is something wrong with the car! I've done everything I can think of. I'm totally stumped and I have no idea what to do?

Why are you using the converter - isn't the Corolla's wiring directly compatible, or don't yours have separate brake and indicator lamps?

Hi oldspark, The Corolla doesn't come with any trailer adaptor or wiring ready. It's basically a 5-way lighting system, and the trailer is a 4-way. The Corolla has separate brake and indicator lamps, whereas the trailer has the brake and indicator lights in the one light (same bulb used with another filament in the bulb). Today after posting I pulled out the instrument panel and checked that over also with a multimeter, and still same problem with random voltage. Then I tried cleaning out the signal stick near the steering wheel, but still no go. I know it could be something simple, but I can't figure it out! So thought I'd post on here to get some input that it might help fix the problem.

You might be better off using a test light rather than a DMM. The "random voltage" may simply be the DMMs average of the flasher on & off time - ie, if it changes between 12V & 0V during the DMM's sampling period. I'd also check each trailer lamp at its plug for proper operation - ie, feed it +12V and ensure all lights. (Can also feed +12V to all except GND to ensure no bad GNDs.)

I've also tried the continuity test light, but no go. That might explain the random voltage, though I've never seen it even reach 10v. But I am still stumped why the system fails for the trailer. I installed a curt wire converter, and since then changed to another curt wire converter. Still same problem. With the trailer, I tested the lights on another vehicle and the lights all work perfect. Tested two trailers, the enclosed trailer and someone's boat trailer on the Corolla and both trailers have the same problem only on the Corolla, not on another vehicle. So it defiantly is the Corolla. Now the trailer lights do work... sometimes! When I turn the indicator lever left, then the left lights signal for the car, and sometimes for the trailer, but mostly fails. Same for the right side as well. It's an intermittent problem. I know the converter has safety features in it, which would shut all power off to the trailer if there is a short or some other inconsistent problem. So it seems the converter/s shut power off depending what the voltage is when I turn the signals on or the hazards on. If I turn on and the voltage seems to be at a nice number, then it all works. Though the indicators will work until I turn off an/or switch to another side of the vehicle for the indicators, then it's the same problem. Very annoying. There's gotta be an underlining problem causing all this!

But now I'm just doubting the whole random voltage thing as it defiantly makes sense the DMM isn't fast enough to read everything! I'm starting to wonder if I should install a new line of 12v of power from the taillights for the trailer turn signals, with a relay that uses the current signal from the car's indicator lights which would get wired through the converter instead of directly from the current turn signals from the car. Do you think that might work? Another solution would be to buy another part completely different to what I'm using now.

Some flasher cans have difficulty driving extra lamps, though combined hazard/flasher cans shouldn't - except perhaps in hazard mode (ie, 6 hi-power bulbs instead of 4). But "slave" flasher bulbs can simply be powered from a normal relay whose coil is across the normal flasher bulbs - ie, switched flasher can output to #86 and #85 to GND. The added bulb power (#30) can be from fused +12V with output #87 to the bulb. However, since you have a combined stop/flasher lamp, you must turn off the stop light whist the hazards or flasher is active (ie, whether the bulb is on or off during flashing).    I'd probably add separate flasher lights and ditch the convertor. The stop bulb could remain as is, or changed to a single-filament bulb. (I'm surprised the trailer uses a dual hi-power filament bulb. Usually it's a single filament since other switching has to disconnect brake light +12V whilst that side's flasher is flashing.)

Do you think changing the trailer lights to an LED system might help? Also thinking of getting a module that get's power directly from the battery like the ModuLite Trailer Light Power Module-119146. I've got a feeling the lights on any trailer draws too many amps from the lights on the car thus the converter cuts off power. I had thought about adding separate flasher lights and ditching the convertor. But, have to register the trailer and have it pass inspection and not so sure on trailer rules around here. Also be good if I could just plug in any small trailer to the vehicle and have it work correctly without needing to install new lighting for each trailer. Thanks for pointing that out about having a combined stop/flasher lamp and needing to turn off the stop light while the hazards or flasher is active. That sounds quite annoying to always have to remember that, especially on a road trip. If I go the relay route, do you have any recommendations where I should gain the +12V power from? Could I get it from fuse box area under the dash? I've provided a photo of the wire which I actually tapped into for the alarm system giving that it's own fuse as well. But that was a different project. So ignore the writing in the photo.

Okay, so here's what I found! First thing, stop-light doesn't work all the time as well, just like the turn signal lights. Defiantly a flaw in the Curt wire converter design that it shuts off. At least that's what it appears. Did an amp test on the trailer light, but it showed about 1+ amp, not much. But probably should have tested from the car itself. Would the location of the amp test affect the reading? Second thing which could be good news! I discovered when inspecting all the lights on the Corolla, that the front indicator/hazard lights are one bulb with two filaments. In other words it is not the same setup at the back, it works as a park light (constant when headlights are on) as well as the indicator/hazard lights when I turn either one of them on via the hazard button or the indicator lever near the steering wheel. So this is something going through my head as to whether if it were possible to run the trailer's wires from the 4-way plug all the way to the front of the vehicle to both Left and Right. So basically, ditch the wire converter and go directly into the indicator/park lights at the front for the trailer's indicators/tail lights. It can't be pulling that much amps? The only problem I'd be left with is the brake lights, again into the same light system. So after all that, maybe I should opt for making my own system with relays to allow that all to work. Slowly I feel I'm getting somewhere.

European towing adapters were 7 pin to allow for separate stop lights indicators with an uprated flasher unit.