Can anyone tell me how I should make the electrical connection for my tow bar?
From what I know there are 2 options: Option 1 Take electricity from the wires running to the cars parking lights, indicator lights and brake lights. Option 2 Take electricity from the pre-fitted connector in the wiring harness in the left tail section of the car.
However: in case 1 I am not sure if the unit sensing broken lights is designed to take the extra current (since the lights will be connected in parallel) in case 2 I am not sure whether the plug was designed to make the connection directly or if there is some sort of control unit between the connector and the pre-installed plug.
I fitted a towbar to my '96 NG900 late last year, and did a fair amount of poking around on the internet to try and determine the best way to wire the electrics up. I also read about the "towbar wiring connector" supposedly hidden beneath the carpet, but I was unable to find it on my car. I completely stripped the boot out, but no connector!
As you mention, it is a bad idea to splice your trailer brake lights directly into the brake lights of the car because you risk frying the blown-bulb-sensor. The Haynes manual shows a purple wire running to the towing electrics which is a spur directly from the switch on the brake pedal (i.e. before the blown bulb sensor) for the purpose of running the trailer brake lights. I was unable to find this wire either (and believe me, I really did look hard :).
So in the end, I decided to isolate the towing electrics from the car's lights by means of four relays. One for the brake lights, one for the tail lights, and one for each indicator. This may seem like overkill, but I thought I may as well do the whole lot, seeing as I was already going to have to relay-switch the brake lights to protect the blown bulb sensor. Plus I already had a separate fused power feed in the boot run from the battery, and a load of identical automotive relays lying around.
Worked for me, but you may do well to get the advice of others on the group in case I've made a glaring error. Don't shout at me if your blown-bulb-sensor thows a wobbler and blows up on you :-)
Something else worth mentioning (even though you may not be in the UK) is that I believe the indicators should have an audible buzzer warning when towing in the UK these days. Legal requirement, I think.
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