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Discussion Starter · #1 ·
I know this is a little off the beaten path for this forum but thought I'd ask anyway. My friend has a 2017 Toyota Tacoma that he pulls his Henry J gasser with on a trailer. All trailer lights and axle brakes worked fine until he replaced the trailer lights with LED lights and now nothing on the trailer works.
The 30amp fuse and relay check out ok. I've read one post that the ECU controls the replay but not sure about that.
He ordered blub lights and got LEDs instead.
Any ideas or fixes?
 

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Gotta love a turbo!
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I'd start by jumping 12v plus/grd to the correct trailer harness pins, see if they light up at all. Might be polarity (prolly not), could be the design of the truck's load circuitry. But I'd think the supply through a trailer harness would be rather generic as there are numerous differences in lighting circuits that should be accounted for.

Russ
 

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Did you change the flasher(s) to no load LED ones?

Checked the wiring with a pigtail tester to ensure no shorts at the truck?

Is the ABS disabled and/or a aftermarket braking controller being used?

Does the trailer ground through the tongue?

Did you use LED conversation bulbs that screw into the old sockets or did you wire the led's possibly wiring them backwards?
 

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RAM pickups and a few others wont run LED s without a load device.
Ram pickups have a TIPM which senses current /circuit operation.Too much load or not enough load BOOM a trouble code sets and the circuit in question is shut down.

Havin fun yet?
 

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Looks like toyota of that vintage has isolation relays (still) for the trailer lighting, unless you hacked into the existing tail/brake wiring at the tail / brake lamp housings.

I would start by checking for a GOOD ground
 

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Old(s) Fart
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RAM pickups and a few others wont run LED s without a load device.
Ram pickups have a TIPM which senses current /circuit operation.Too much load or not enough load BOOM a trouble code sets and the circuit in question is shut down.

Havin fun yet?
Yet another reason why I'm getting rid of all my vehicles that have electronics and only owning pre-computer cars. ;)
 

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Discussion Starter · #10 ·
Looks like toyota of that vintage has isolation relays (still) for the trailer lighting, unless you hacked into the existing tail/brake wiring at the tail / brake lamp housings.

I would start by checking for a GOOD ground
Please expand on " isolation relays" and there location.
 

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Old(s) Fart
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Please expand on " isolation relays" and there location.
Unlike older cars and trucks, many newer vehicles use a separately-fused circuit to operate trailer lights. The light, brake, and turn signal switches in the towing vehicle don't operate the trailer lights directly, they simply switch a relay on and off. The relay then powers the trailer lights from a separate fuse and power source. The advantage is that now a trailer wiring fault won't short out your tow vehicle, which is especially important in newer vehicles where voltage spikes can fry electronics. The relays can be located anywhere, depending on the manufacturer. I know that new GM vehicles have the relays in the underhood relay center.
 

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Please expand on " isolation relays" and there location.
In the underhood fusebox

look for towing tail relay
stop relay
The turns are straight from the instrument panel
The wiring for the towing brake controller comes right from the controller

If you have no OE controller , chances are you do not have the towing package
Also, the turn signal switch is wired to the instrument cluster and flash function is controlled by the cluster
Probably not a good idea to use a rgular relay to tap ito th turn signals as flyback voltage (spikes ) can damage the cluster. Best to use a solid state type of device to keep circuit load to a absolute minimum.
The safest tow adapters have an auxiliary power wire to run the circuit, and only use the flasher signal as a on off bias (signal) for the solid state device (towing light adapter)
 

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This is similar to what I am talking about.
This one adapts a system that has seperate turn signal circuit from the brake signal circuit
Should work on your toyota since you have turn and brake seperate in the rear lens
Uses only a fraction of current from the truck circuitry to run the trailer and isolates the trailer wiring, since most railers are kinda shoddy in the wiring department LOL
 

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Yeah , electronic gizmos in vehicles gets crazy. Thankfully I have no issues with LED lights on the trailers I pull with my 2021 F-350 Ford truck. Years back Aftermarket LED tail light conversions would cause problems with converter clutch operation of the transmission of Ford trucks.
 
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Discussion Starter · #18 ·

This is similar to what I am talking about.
This one adapts a system that has seperate turn signal circuit from the brake signal circuit
Should work on your toyota since you have turn and brake seperate in the rear lens
Uses only a fraction of current from the truck circuitry to run the trailer and isolates the trailer wiring, since most railers are kinda shoddy in the wiring department LOL
Couldn't find a wiring diagram but read a post that said the ECU controlled that relay. I'm thinking the LEDs don't pull enough power to tell the ECU to active the relay.
 

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the 'Duracell Project'
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That's irrelevant for a trailer. The lamps in the vehicle already provide enough load for the flasher to work, obviously. And frankly, I doubt any 2017 vehicle still uses a mechanical flasher.
my 09 gmc has separate fuses and flasher for the trailer, though i agree with the mechanical flasher comment
 
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