Tinus - thanks for the prompt about OHM's law - its all about voltage drop at the actual point where wires connect to the globes. I am no expert but "Google is your friend" .... !
I suggest when engine running and lights on bright, measure your voltage at the battery, and also at the point where wires connect to the bulbs - if there is a voltage drop (more than about 0,2v = about 5% loss in light efficiency) then you are losing energy in the wires - then you should upgrade the wires and possibly the relay.
Found an article on the web, heres a short extract:
In many cases, the thin factory wires are inadequate even for the stock headlamp equipment. Headlamp bulb light output is severely compromised with decreased voltage. The drop in light output is not linear, it is exponential with the power 3.4. For example, let's consider a 9006 low beam bulb rated 1000 lumens at 12.8 Volts and plug in different voltages:
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
The Europeans take a slightly more realistic with their voltage ratings; they consider output at 13.2v to be "100%". The loss curve is the same, though. When operating voltage drops to 95 percent (12.54v), headlamp bulbs produce only 83 percent of their rated light output. When voltage drops to 90 percent (11.88v), bulb output is only 67 percent of what it should be. And when voltage drops to 85 percent (11.22v), bulb output is a paltry 53 percent of normal! It is much more common than you might think for factory headlamp wiring/switch setups to produce this kind of voltage drop, especially once they're no longer brand new and the connections have accumulated some corrosion and dirt.
Its a very interesting article - for a better understanding read it here:
http://www.danielsternlighting.com/tech ... elays.html
if it is necessary to get these for my 1998 4.5 GL? Is the wiring of the car good enough or will the harness make a noticeable difference to my headlights? My car got the bulbs in that I bought it with. I am not to sure what the watts of the bulbs is. Has any one done the replacement of their lighting harness? 
