Rear Lights Dim

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gollfy
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Rear Lights Dim

Post by gollfy »

Hi All,

My rear lights look abit dim, I have measured the voltage to the rear fog light and can see about 10.5volts.

After reading the sticky I have cleaned the earth on the left hand side of the engine bay and checked the light connections and cleaned them.

Is there anywhere else to check? Is around 10/11v the norm?

Cheers
Dave

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bigherb
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Re: Rear Lights Dim

Post by bigherb »

gollfy wrote:Hi All,


Is there anywhere else to check? Is around 10/11v the norm?

Cheers
Dave
Is that with the engine running?
And have you got the correct 10W sidelight bulbs in
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CovKid
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Re: Rear Lights Dim

Post by CovKid »

They were never that great to start with. :cry: Mine match modern cars now but had to completely gut the bulb holders and go over to LED panels to fill each void. :)

You can't go greater than 10w in tungsten either or it will melt the lenses.

Image - they fit ULO rear lights but not Hella. Almost no heat generated either.
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captain Byrne
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Re: Rear Lights Dim

Post by captain Byrne »

Swapped all my rear bulbs for these. Much better and not too bright so they dazzle.

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CovKid
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Re: Rear Lights Dim

Post by CovKid »

Most Chinese-made LED lamps tend to be over-driven though which makes their life even shorter than tungsten. Its hard to get LED bulbs on arrays that don't start to fail after a time, usually one LED, then two, until they all fail. Got a box full of naff ones. Its possible to increase the value of the resistor slightly to extend their life but otherwise these plug-n-play ones have a long way to go before they're a really good alternative. Quality control is usually non-existent.

That said, I'm a big advocate of LED lights generally. You just have to rely on ohms law to gauge life expectancy. I managed to get mine within tolerance using additional resistors.
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Re: Rear Lights Dim

Post by crazyhorse »

CovKid wrote:They were never that great to start with. :cry: Mine match modern cars now but had to completely gut the bulb holders and go over to LED panels to fill each void. :)

You can't go greater than 10w in tungsten either or it will melt the lenses.

Image - they fit ULO rear lights but not Hella. Almost no heat generated either.

Nice tip, any ideas on how to fit these and where to get them??

Could you do it with front indicators??

Maybe another one of your detailed guides are in order :D
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gollfy
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Re: Rear Lights Dim

Post by gollfy »

10.5v without engine runnning, they look the same with it running tbh. I only measured the voltage at the fog light because that seems to be the one that is not very bright

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937carrera
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Re: Rear Lights Dim

Post by 937carrera »

What wattage bulb is fitted in your foglight ?
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Re: Rear Lights Dim

Post by CovKid »

Try measuring voltage at headlight. If that too is poor, try this: http://wiki.club8090.co.uk/index.php/VW ... ry_to_dash" onclick="window.open(this.href);return false;

Bear in mind that all the lights are fed by a 6mm cable which is barely adequate. Also make sure earth crown is clean. The single biggest difference I ever made to my lights was upgrading the main cable to dash (as above) and renewing main cables underneath:

http://wiki.club8090.co.uk/index.php/VW ... ain_cables" onclick="window.open(this.href);return false;

Many try to get around the prob by changing bulbs or fitting ones of greater wattage but that just makes things worse, further overloading circuits. The answer lies in the supply line. VW were far from generous when it came to power cables - plain mean I'd say.

I run with standard headlight bulbs (not Osrams etc) and my lights are bright as hell now. On full they light up the entire street.

I'm sure others who followed my lead on this will vouch for the massive difference it makes. If you scrounge around for suitable cable, it need not cost a fortune either. I only did the upgrades because the back lights were so poor, I was scared witless someone would run into the back of me one misty morning. :shock:
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937carrera
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Re: Rear Lights Dim

Post by 937carrera »

gollfy wrote: I only measured the voltage at the fog light because that seems to be the one that is not very bright

Looks like he only has a problem with the foglight, hence the question about the wattage, in case the wrong size has been fitted.

The 10.5v looks low, but unless we know the condition of the battery it's hard to conclude anything directly. I just checked on one of my vans. 12.7V at the battery, 11.96V at the tail light, using the tailgate latch as the earth point, so only 0.75v voltage drop.
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Re: Rear Lights Dim

Post by CovKid »

Rough guide to show how much is lost on say a headlight, due to voltage drop

10.5V : 510 lumens
11.0V : 597 lumens
11.5V : 695 lumens
12.0V : 803 lumens
12.5V : 923 lumens
12.8V : 1000 lumens ←Rated output voltage
13.0V : 1054 lumens
13.5V : 1198 lumens
14.0V : 1356 lumens ←Rated life voltage
14.5V : 1528 lumens
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RogerT
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Re: Rear Lights Dim

Post by RogerT »

The wiki has helpful info on voltage drop and light output drop not being linear. There’s a graph of Hella’s published light output figures. 10% voltage drop (i.e. 11.34v vs 12.6v) gives a light output drop of 35%.

http://wiki.club8090.co.uk/index.php/VW ... headlights" onclick="window.open(this.href);return false;

I’ve done Covkid’s wiring upgrade and the difference was staggering. Don’t have measurements but I was much more confident that I could see where I was going!
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CovKid
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Re: Rear Lights Dim

Post by CovKid »

Thanks - I think one or two have done this upgrade now and its by far the best upgrade on the electrics you can do. The effect is WAY better than fitting Osrams.

Aye, I think its easy to underestimate the impact of voltage drop. Before I renewed main cables, I fitted a voltage meter on the dash. Most of the time it was around 10.5 volts with the headlights on, even with battery voltage and alternator reading fine. Once I renewed main and fusebox feed, this jumped to 14 volts. Thats a significant difference, and why I say compensatory measures like brighter bulbs and upgraded alternator regulator, miss the point entirely.

With regard to the foglight, I'd still take readings elsewhere so you can completely rule out the possibility of frayed or failing main cables. 30 years is a long time and I've yet to see an untouched T25 without corrosion/damage to main supply cables, and bear in mind they were just adequate when new. If the rest do have better readings then earth crowns and any connectors in the foglight circuit need checking for corrosion and/or heat. Certainly the 6mm feed from battery to fusebox can get warm once the electrics are under load and heat means resistance - thats what prompted me to rethink the supply lines. Check where it terminates at fusebox. Its not uncommon to see melted plastic around it.

Finally, the reflectors in rear lights are often pi$$ poor. With tungsten, these reflectors are crucial to good illumination. It matters not with an LED panel, but with bulbs it means everything. It tried all kinds of things in the early stages, including merc truck lights for comparison. It took a while but I now have crisp bright lights front and back that match every other vehicle on the road instead of something from the 1950s :)
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Re: Rear Lights Dim

Post by silverbullet »

A new battery earth and an additional earth from engine block to chassis made a huge difference to starting and headlight output.

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Re: Rear Lights Dim

Post by CovKid »

Yep, all part of the circuit.
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