towbar wiring harness for 70 series land cruiser

Submitted: Thursday, Mar 20, 2014 at 21:18
ThreadID: 106813 Views:7606 Replies:3 FollowUps:0
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Can any one throw some light on why towbar wiring is either a simple cut and splice into rear wiring harness or a factory/Toyota relay? based system running from engine bay. I have been told that if the caravan has lots of external lights then standard wiring harness is not up to it but it is ok for a trailer. only interested in 70 series requirements.

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Reply By: Ross M - Friday, Mar 21, 2014 at 14:29

Friday, Mar 21, 2014 at 14:29
Grey YesMad
I don't own a 70 series but a general comment.

With a caravan or trailer there is no difference, it is the number of operational lights fitted ie, multiples of Brake lights, multiples of Park lights and also indicators which may have a few side repeater lights.

So it is the multiples of which are the issue and the amp loading.
Besides the load on the wiring the multiple flashers ie. more and more will usually affect most flasher systems UNLESS the vehicle has a rate controlled flasher unit.

After knowing what the system has, then the issue of the vehicle's ability to supply and not cause voltage drop or heating in the vehicle loom is also to be considered.

The issue of LED lights is another thing. Usually an ALL LED trailer/van will have not much problem running lights from the vehicle.

Some vehicles use two relays driven by the flasher unit so the trailer/van Indicator lights run, and don't affect the vehicle flash rate.
If there is heavy loading of tail light circuit or stop lights ie multiples then the Tail lights and stops can be relay driven too. While your at it a reverse through signal through pin 2 could also be done if required.

Having a heavier feed wire from the battery to the rear, 2, 4 or even with reverse, 5 relays could be switched by the vehicle wiring with minimal/almost zilch vehicle loading and the outputs of the relays run to the trailer plug and all lights therefore run from that heavy wire.

Dmax has towbar with two relays which do this but not the other functions. other vehicles are now following. Used also on CANBUS systems so the vehicle isn't affected in anyway.

It is all your choice of course, but not 70 specific but the same issues apply.

PS the good thing is, when checking, you can hear the relays switch on and know what should be working and when.
Ross M
AnswerID: 528797

Reply By: Notso - Friday, Mar 21, 2014 at 19:18

Friday, Mar 21, 2014 at 19:18
I've got a mate with one of them and the best thing to do is fit the factory system. Most of the modern vehicles use a "Black Box" to run the trailer. They have their own separate fuses. Make sure when you get it fitted to get the Auto Elec to show you where the fuses are.

We were off travelling with the mate when he lost his rear Brake and Turn indicators. It took us, an auto electrician and about 3 hours to find the flaming fuses tucked away behind the battery.
AnswerID: 528815

Reply By: Member - Stuart P (WA) - Saturday, Mar 22, 2014 at 00:37

Saturday, Mar 22, 2014 at 00:37
the only reason for the genuine toyota wiring harness and relays are for supplying power to the indicators . the relays are to supply power to the front indicators in the headlight cluster and to the indicators to the trailer plug , the factory wiring is not up to the task of the bull bar indicators or the load to the trailer plug
AnswerID: 528845

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