Trailer leds dim indicators

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Tonydrum

11 posts

Geek

#267959 19-Feb-2020 17:37

Ok so I replaced my tail lights on me old truck with leds, due to hyper flash I installed load resistors on them. Now I have built a trailer, and fitted leds to that as well. The problem I have is that I’m only getting 9v to the trailer lights, I’m assuming it’s the load resistors doing their job . How ever the trailer indicators are dim. I have put a clean earth the truck chassis. The truck lights are working fine still. Just the trailer is a problem. Any help would be great.

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73 posts

Master Geek

#2424161 19-Feb-2020 17:47

Take the pickup for the trailer from the loom side of the resistors not the resistor output to light side ?

Tonydrum

11 posts

Geek

#2424169 19-Feb-2020 17:53

Yer so I thought that and taped one indicator into the loom before it gets to the the resistor. No joy! Beginning to think of wired the resistors wrong. So they work fine until there is a trailer in the circuit.

Tonydrum

11 posts

Geek

#2424180 19-Feb-2020 18:37

Just pulled a front indicator (still bulbs) and that’s running 9v as well. Maybe it’s the relay?

k1w1k1d

1527 posts

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#2424254 19-Feb-2020 21:19

Did you install the resistors in parallel with the rear LED's?

Make, model, year of "old" truck?

Tonydrum

11 posts

Geek

#2424257 19-Feb-2020 21:22

Yes I did. Truck is a 97 Mazda bounty. When I disconnect the resistor I get hyper flash on both the truck and trailer and not dim.

Tonydrum

11 posts

Geek

#2424263 19-Feb-2020 21:32

I’m running 12v 21w resistors. Is the wattage to high?

Technofreak

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#2424278 19-Feb-2020 22:19

Tonydrum: I’m running 12v 21w resistors. Is the wattage to high?

There is no such thing as a 12V 21w resistor. Resistors are always Ohms.

The resistors will have a wattage rating but this won't directly affect how things do or don't work. If the wattage is too low the resistor will burn out. A higher than necessary wattage will not matter at all, except the resistor will be physically larger than necessary and the resistor will not get as hot.

Can you draw a diagram of how you have it wired and post that on here? Then it will be easier to provide some help.

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Tonydrum

11 posts

Geek

#2424288 19-Feb-2020 23:18

An image of the load resistor I’ll draw up a wire diagram tomorrow.

https://cdn.geekzone.co.nz/imagessubs/63d6e4b882850ec601017ed37e266721.jpg

Handle9

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#2424298 20-Feb-2020 01:52

Technofreak:

Tonydrum: I’m running 12v 21w resistors. Is the wattage to high?

There is no such thing as a 12V 21w resistor. Resistors are always Ohms.

A 21W @12V resistor is ~7 ohms. If you know any two of power, ohms, voltage or current you can derive the rest from ohms law.

Resistance is always measured in ohms but a resistor can be described by other things.

Technofreak

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#2424319 20-Feb-2020 08:50

Handle9:

Resistance is always measured in ohms but a resistor can be described by other things.

Just pop into Jaycar or try to order a 12V 21 watt resistor through Element 14 etc. Don't think you'll find there's such a beast.

The wattage is the maximum amount of power the resistor can dissipate without damage to the resistor. Resistors are sold/named by their resistance and the wattage they can dissipate. Voltage doesn't come into the equation.

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Yoban

447 posts

Ultimate Geek

#2424331 20-Feb-2020 09:21

Seems very similar to @chimera https://www.geekzone.co.nz/forums.asp?forumid=141&topicid=265668 Maybe some tips there which you may have already seen.

1101

3122 posts

Uber Geek

#2424351 20-Feb-2020 10:02

Put the resistor in PARALLEL , not series .

Series resistor would allways drop the voltage , hence dims LEDs .

Fred99

13684 posts

Uber Geek

#2424430 20-Feb-2020 11:06

I'm not sure if this is relevant, but I had a 4WD with 24v electrics when I bought a new trailer, the supplier (Kea) replaced the standard 12v LEDs with 12/24v units as part of the deal (IIRC it was supposed to have been a $70 upgrade). I've lent the trailer to many neighbours, it's been towed with an assortment of new-ish vehicles - off the top of my head - a Ranger, Landrover Disco, Hyundai, Mitsu Outlander, BT50, Mazda CX5, D-Max. I'm not aware that there's been a problem with lights/indicators when towing with any of them.

Technofreak

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#2424463 20-Feb-2020 12:27

Tonydrum: An image of the load resistor I’ll draw up a wire diagram tomorrow.

https://cdn.geekzone.co.nz/imagessubs/63d6e4b882850ec601017ed37e266721.jpg

That the nomenclature on that resistor tells me it is simulating the load of a 12v 21 watt bulb. It is not necessarily a 21 watt resistor.

You probably need one connected in parallel across each led light fitting to simulate the load that would have been drawn by an incandescent bulb at that location.

I suspect you might have one fitted in series somewhere if you're not measuring 12 v at the bulb location, or you have a earth problem or something similar.

They are probably a stupid price from Narva and can be sourced else where.

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Tonydrum

11 posts

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#2424466 20-Feb-2020 12:34

It sounds to me that I have wired the resistors in wrong I’ll have to re look at them. Great information guys thanks heaps I’ll up date you after Iv tried to re wire them tonight.

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