Trailer wiring

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Trailer wiring

Postby Hiawatha » Thu Jun 18, 2015 10:54 am

I replaced the tail lights on my trailer the other day , the old ones had had a few too many knocks . The Discovery has a very useful feature that illuminates a trailer symbol on the dash whenever a trailer is connected and the indicators are used . This is a handy check on bulb function and serves to remind you that you do in fact have a trailer hitched to the rear [ an unloaded 6x4 trailer is almost invisible behind the tailgate from the driver's seat ] .
This facility doesn't work with the new lights , they are much the same as the originals , not LED or anything fancy , just straightforward Narva bulb clusters .
What actually activates this light ? I had thought it was some type of earth current sensor , I am at loss to understand why the new lights are acting differently . The wiring is the same as the last , I just hooked up the existing cables . Any thoughts ?
-------- 1952 TED, 1957 FE35 Grey and Gold Deluxe
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Re: Trailer wiring

Postby White Wolf » Thu Jun 18, 2015 11:53 am

The Disco trailer symbol has some sort of load sensor to make it work. My Disco has extra front indicators in the bull bar so the trailer symbol always lights up, unless one of the globes blow.
Narva are generally good quality so I assume the indicator globe are of the correct wattage and therefore will draw the required current to trigger the dash light. I would double check all the indicator lamps on the car, including the side repeaters are working properly because if one of these are out the load even with the trailer lights will be insufficient to activate the dash light. I often check the trailer and car lights are working by activating the key fob. The car must also have a load sensor to check both sides are balanced, one time when discovering one trailer light out I turned the hazard lights on while I investigated the problem, the car had a hissy fit unless all lights were working or no trailer lights were working. Turned out that one of the globes had been shaken out of its socket.

I wonder if Lucas were responsible for inventing the flashing indicator as well as the intermittent windscreen wiper.
1950 TEA, 1962 MF35 petrol
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Re: Trailer wiring

Postby Hiawatha » Thu Jun 18, 2015 10:17 pm

White Wolf wrote:I wonder if Lucas were responsible for inventing the flashing indicator as well as the intermittent windscreen wiper.


Their latest innovation is the intermittent headlight circuit ! :) Thanks WW.
It sounds like the wattage of the bulbs and hence the load on the circuit is the trigger [ a hysteresis sensor from memory ] , the bulbs are fairly low power , only ten Watts . I will try some higher wattage bulbs on the indicator circuit today .
-------- 1952 TED, 1957 FE35 Grey and Gold Deluxe
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Re: Trailer wiring

Postby White Wolf » Thu Jun 18, 2015 11:40 pm

I think indicator and brake lights are generally 21 watts.
1950 TEA, 1962 MF35 petrol
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Re: Trailer wiring

Postby Hiawatha » Sat Jun 20, 2015 12:15 pm

21 Watt bulbs in the indicators solved the problem WW. Thank you for the tip . It stands to reason then that if you replaced your extra indicator bulbs with ones of a lower Wattage the trailer indicator may not come on all the time . Or better still use LED replacements that have a much lower current drain and high Lumen output .
-------- 1952 TED, 1957 FE35 Grey and Gold Deluxe
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Re: Trailer wiring

Postby White Wolf » Sat Jun 20, 2015 1:11 pm

Glad you had an easy fix Hiawatha. It is on my to do list to replace the sun damaged bullbar lights with new brighter LED lights. Doing so won't help me if the trailer lights are working as I've already converted them to LED. My tandem trailer has eight tail/marker plus the number plate light, when braking or indicating I could see the side markers were dulling. Replacing all the lights with LEDs and improving the joins in the wiring (i can't believe how slack trailer manufacturers are the wires were just twisted together and wrapped in tape) has fixed the fading lights.
1950 TEA, 1962 MF35 petrol
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