Tail Light Resistors

[Classic49]

I thought I'd have a go at renovating my rear lights following Andrew Smith's article in the latest mag. I have discovered a resistor (Lucas 4BR) in the circuit to each tail light bolted to the rear of the light unit but it doesn't seem to appear in the wiring diagram. This is not the same as the night dimming relay which I have already disconnected.

Does anyone know if this serves any useful purpose other than further reducing the brightness of the lights?

Simon

[ChasR]

Where are the resistors?

If they are in the indicators there is a good chance that they are load resistors if the car once had LED indicator bulbs fitted.

[Classic49]

Where are the resistors?

If they are in the indicators there is a good chance that they are load resistors if the car once had LED indicator bulbs fitted.

They are definitely wired to the tail light only and are bolted on the boot panel using one of the light unit fixing bolts.

[norstag]

Hi Simon, the resistors are definately original equipment I remember removing them from my car in an effort to get the lights brighter, but I can't remember which lights they affected and under what circumstances, I can't find them on the wiring diagram either. Alan

[Pete]

You could use the voltage difference across the resistor to feed warning lamps about bulb failure, but I guess it is better to have bright lamps.

[mallardstag]

What's the voltage on either side of the resistor with the lights switched on? T

The Lucas 4BR resistor has a resistance value of 3ohm and is usually used to provide the slow-speed blower resistance in some cars. A 5 Watt tail lamp consumes about 0.4 Amps at 12 Volts and this equates to a hot lamp resistance of about 30ohm so I can't see a 3ohm resistor making that much difference.

Confused,
Simon

[Classic49]

What's the voltage on either side of the resistor with the lights switched on? T

The Lucas 4BR resistor has a resistance value of 3ohm and is usually used to provide the slow-speed blower resistance in some cars. A 5 Watt tail lamp consumes about 0.4 Amps at 12 Volts and this equates to a hot lamp resistance of about 30ohm so I can't see a 3ohm resistor making that much difference.

Confused,
Simon

There's a 2 volt drop so bypassing the resistor certainly improves the brightness. I just don't understand why they should be there.

[brian0443]

A real puzzler. So both Simon and Alan have cars which have/had these resistors. Are the cars early, same years or anything like that? Did they also have the dimming relays, which presumably did not operate on the tail lights since these would only be on at night anyway.
Brian

[Classic49]

A real puzzler. So both Simon and Alan have cars which have/had these resistors. Are the cars early, same years or anything like that? Did they also have the dimming relays, which presumably did not operate on the tail lights since these would only be on at night anyway.
Brian

Brian

Mine is a 72 Mk1 Stag (LD105130) and has the dimming rellay which I have taken out of operation by disconnecting the earth wire.

Simon