Which "fog light conversion"??? yes, again...

Right, Ive trawled through and read up on using the 2 inner brake light to fog light conversion threads, and theres alot of them lol

1 way is using the relays and resistors and 1 uses JUST 2 diodes in suitable places. Both seem to give the same effect.

I want to do this mod to my Aristo, but am unsure of which method to do it. Ive noticed some people say the diode only way isnt the correct way but then others have done it this way with no problems at all

Obviously its a J spec car, if that makes a difference and I already have a +ve feed to the back of the car with a switch & fuse etc

Any advice would be good, cheers

Had two diodes on my UK spec (facelift rear lights) for years without problems. Others seemed to frown upon it at the time and prefered to use relays etc?

Why make things more difficult than they need to be?

i just stuck a red bulb in one of the reverse lights and ran a new switch wire.

Hmmm, well I may have to try the diode method

Thats what Ive done first but it doesnt look anywhere near bright enough to pass as fog light Its with an 24 LED bulb too

Hi Chris,

Neither way is incorrect, however my recommendation would be to use a relay if you are not familiar with diodes or circuit design. Using the wrong diodes, or connecting them incorrectly, will rapidly result in melted diodes and possible damage to the vehicle circuits feeding them. You are more likely to wire up the relay correctly.

If you are using 21W incandesant lamps and are using a pair of diodes for each lamp, the diodes will need to be capable of carrying 2A continuously, with sufficient cooling to dissipate about 1.75W. If you are using a pair of diodes to feed both lamps the current and power ratings will need to double. I would opt for dual TO220 devices with insulated tabs so they could be fixed to some convienent metalwork for cooling.

Using diodes will result in the lamps, fed from the diode, being slightly dimmer than thoes fed directly. This is due to the 0.8V – 1.0V lost across the diode.

If you are using an LED array as a lamp, the current will probably be a lower, and it is possible you may be able to adjust the series resistor to counter the voltage drop of the diode.

For your information I have used a relay.

I’m not sure why you suggest resistors are needed with the relay though !

Hope that helps

Mark

re read replies

Hi Chris,

 

Neither way is incorrect, however my recommendation would be to use a relay if you are not familiar with diodes or circuit design. Using the wrong diodes, or connecting them incorrectly, will rapidly result in melted diodes and possible damage to the vehicle circuits feeding them. You are more likely to wire up the relay correctly.

 

If you are using 21W incandesant lamps and are using a pair of diodes for each lamp, the diodes will need to be capable of carrying 2A continuously, with sufficient cooling to dissipate about 1.75W. If you are using a pair of diodes to feed both lamps the current and power ratings will need to double. I would opt for dual TO220 devices with insulated tabs so they could be fixed to some convienent metalwork for cooling.

Using diodes will result in the lamps, fed from the diode, being slightly dimmer than thoes fed directly. This is due to the 0.8V – 1.0V lost across the diode.

 

If you are using an LED array as a lamp, the current will probably be a lower, and it is possible you may be able to adjust the series resistor to counter the voltage drop of the diode.

 

For your information I have used a relay.

I’m not sure why you suggest resistors are needed with the relay though !

 

Hope that helps

 

Mark

I suspect he's referring to the resistors needed to fool the bulb fail ECU when the fog circuit is in use.

Mike

When I got my car the inner 21W lamps were wired as fog lights only.

So either the bulb fail ECU has been frigged to work with one set of light or disabled. I shall investigate further..........

Thanks Mike

Thanks for the replies guys, and the info on the diode method Mark.

I think after reading the 2 relay guide over a few times, Im now more familier with what needs doing so Ive sinced ordered the relays and resistors from Maplin, and will be doing it that way

And yes, Mike was right about the resistors being used for the bulb failure light fix

Been doing this today for my Aristo, and it works, 1st time aswell and the bulb warning light stays out too

Great guide

Also, on the Aristo it can be pretty much all wired and connected up off of the car due to the loom disconnecting about 15cm from the bulb holders, so these can be removed with it Ignore the red bulb also, its now back to a standard reverse bulb

A few pics.....

Tail lights

Tail & Fogs

Fogs with brakes

Brakes only

I was thinking of mounting it all inside the boot lid but then decided it would be a bit tight with trying to get the boot trim panel over the top of it, and due to the boot being opened and closed it probably wouldnt do the relays alot of good so extended the necessary wires down the corner of the boot behind the trim panel