When I turn bedhead lights on my 12v tv goes off in caravan

A vehicle is 12 volts not 240v. You will blow fuses and burn wiring putting 240 into 12v. What kind of car or truck is this?

Get the wiring standard for trailer socket on car / caravan .
Something like this
http://www.caravantalk.co.uk/caravan-advice/new-to-caravanning/electrics-guide/12-volt-systems
Then get a 12v probe and test the voltage is coming out the correct pins on the car when the tail lights are turned on.
http://www.amazon.com/6-36V-Circuit-Test-Probe-Indicator/dp/B0065R1CK4
Check the Earth Connections on the caravans tail lights.
Check the Caravan has an earth connection to the car body.
https://caravanchronicles.files.wordpress.com/2012/01/caravanchronicles-wiring1.jpg
see how pin 3 shows an earth wire it would have a wire on car socket pin 3 going to the car body. If the earth wire is corroded or broken I think the tail lights on the caravan would not work. It may be a different pin on your setup .

http://www.narva.com.au/products/browse/wiring-diagrams

use a volt meter to work out which light is connected to which pin on Ford Ranger trailer plug . Hopefully it corresponds to standard trailer wiring diagrams. Test each wire could also use a light bulb with two wires soldered to it or a 12v dc probe.
http://www.amazon.com/6V-12V-24V-Motorcycle-Circuit-Voltage-Electroprobe/dp/B00GYVS0E2
http://www.ebay.com/sch/i.html?_ssc=1&_nkw=Voltage+Detector+Tester+Pen+Non-Contact+Probe+Pen&_sop=7

The ground is aso controlled based on the neutral safety switch input

check for a bad ground, this can make lights do weird things

You Put the instrument cluster in self test mode.

Well, the connector u can buy frm the particular company shop!! but for supply reazon, u hv to desgin plug for particular given vols..or just buy the normal adaptor or variable adopter
and get connect he 4 pin plug on that and enjoy!!

before going after the starter, check the battery and connections. battery must have at least 12v and should be able to withstand a 200amp load for at least 15 seconds to check out as good. I think your starter is on the bottom side of the engine facing the radiator. easiest way to find it is to follow the positive cable from the battery...it goes right to it.

check the fuse and relay that control the power window, check the power window switch by turning on the doom light, depress the switch, if the light dims then its working, remove the cover and check the motor for proper operation by adding 12v to same. check to make sure the window is still the grove and the grove is free from debris

May be with other accessories like radio, or something. Might need to purchase a cheap 12v test light. Always good to have one around for such problems.