Tail lights inter-working with RV towing connection
The very purpose of this car, be flat-towed by a RV. I looked around and discovered that a very limited number of cars can be flat-towed safely with no risk of damage to transmission/differentials.
In summary, most automatic transmission vehicles are not candidates, so I was left looking for a cheap option, ideally 4 wheel drive, in a small list of options. This old manual 1995 Jeep Wrangler popped up in my search, which had already been flat-towed and even included the towing setup, arms, etc.
The previous owner made an attempt to use the car's own rear lights to carry the RV's lighting, but ended up using an additional light rig that needs to be installed from front to back, outside of vehicle. This rig has two simple lights that are attached to the rear bumper with magnets. I used this for the first few trips while I investigated what would take to use the car wiring and lights.
One thing that I suggest to anyone getting into electric work is to first of all, get yourself a maintenance manual or specific electrical diagrams of circuit that is been analyzed.
I did some research online and found this website where I was able to grab all electrical diagrams for this vehicle, I found it online for $20. Without an electrical diagram, I would not be able to figure this out.
When looking into the diagram for "external lights", observed that both rear turn/stop lights were connected together by the turn switch in the steering column, when lever rest in the OFF position (center, no turn lights activated).
Because of this small detail, if an external source of power (RV) is connected to the vehicle's rear turn/stop wiring, a malfunction happens as both wires for right and left turn are short circuited.
Needless to say that each right and left circuit needs to work independently, while the parking lights work both right/left simultaneously. As seen below, parking lights are connected together and in theory, should work without and modifications. However, I implemented the same changes I did to the turn/stop lights, just in case.
IMPORTANT : Before starting any work, make sure that you disconnect the car's battery.
Before next step, let's talk about the actual solution for the issue and what a "diode" actually does.
As discussed, we need to have independent connections to the turn/stop lights, so the RV can be connected and work properly when a left turn or right turn signal is used. The easiest way to accomplish this is with a electronic component called "diode", which is a semiconductor built as such that the electrical current can only travel in one direction. Showing below the representation of a diode:
Using this principal of one direction flow, we can easily implement an "isolator" circuit, as shown below:
This configuration allows both RV and vehicle to power the rear lights, installed under dashboard near the connector coming from steering wheel column (including turn sign lever switch).
When choosing a diode for this purpose, considerations should include the max direct current and max reverse voltage. The max current should be higher than what the light bulbs can consume and the max reverse voltage higher than 12 volts.
Diode 20SQ050 was selected, with max current of 20A and max reverse voltage of 50 volts, from Amazon at $8 for 25 pieces.
Installing this solution requires some level of proficiency in simple electrical work, including splicing, soldering and isolating wires.
The wires to be spliced runs in the harness going from dashboard to the rear of vehicle. This bunch of wires packed together runs inside the steel frame of vehicle on the driver's side and it can be "fished" at different places. In my case, I decided to work under the dashboard, right at the plug connecting wires coming from the turn switch and hazard switch in the steering wheel, as well as the wire coming from the parking light switch.
TO BE CONTINUED
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