The wire for my headlights in the main wiring harness in my S4 must have melted because they suddenly stopped receiving power and when I tried connecting a relay to the parking lights in an attempt to temporarily re-enable the headlights, they started working again.
Because everything seems to be running without any problems now, I'm considering just keeping things the way they are.
Could any potential problems come from having the headlights wired in this manner?
What I'm particularly concerned about is the headlight switch unit because I've had one melt in the past because an excessive amount of current was flowing through the unit due to carbon build up on the headlight plugs. I'm worried that something similar might occur because a relay does pull extra current to activate the coil.

 

Series four only.

Headlights only.

You turn the headlight switch to full ON.

This connects the BLACK wire in the headlight switch to the Red/White wire in the headlight switch which in turn puts a ground on the Headlight relay up front near the radiator. The headlight relay pulls in and feeds power from the headlight fuse in the engine bay to the headlight assy's.



The power that lights up the headlight beams does NOT pass thru the headlight switch.

The Green/White wire on the headlight SWITCH, has nothing to do with the HEADLIGHTS coming on. It's the White/Green wire in the headlight switch plug that melts and ruins the plug. Therefore carbon buildup on the headlight plugs can't possibly cause a headlight failure.

The White/Green wire supplies power to the front and rear side lights and *dash lights*.

I've never head of the BLACK (gnd wire in the switch plug) nor the Red/White wire ever melting and causing a headlight failure or headlight switch failure.

Just clearing up on How Things Work. Not answering the question.

 

Well what happened when my switch melted was that the fuse which enables all the lights in the car blew, so I replaced it, and it blew again, so I put one in that could handle an extra 5 amps, and this time it didn't blow. But after driving for about 10mins I started to notice the smell of melting plastic, which was my headlight switch melting.

When I got home I tested to see if the headlights would work with a separate circuit, one connected directly from the battery to the headlights. One of the lights worked but the other didn't, instead it started to smoke. So I checked the plug and it appeared to be very aged so I replaced it with a new one, and everything started to work again.

So it seems that the plug caused the headlight switch to melt. If as you say the current that the headlights draw from the battery does not pass through the headlight switch, then I'm guessing that the activation current for the coil in the relay must have somehow increased, and that is what caused the melting to occur.


What are the front and rear side lights, do you mean the parking lights for the front and the red non brake lights at the back?

If this is the case then I guess it's probably not a good idea to run a relay off of the parking lights.
Why is it that the White/Green wire causes the switch to melt? Can this be circumvented?

 

It's a fault inside the headlight switch that causes the white/green wire to melt.

The WHITE/GREEN wire feeds the lights shown in the attached jpg. The tail lights, side marker lights front and rear, liscence plate lights etc. Any light fed by the R/B wire is what I'm saying. The white/green wire feeds the R/B wire when the switch is turned to on (the first positon when turning the switch **** to on).

Not good to use a higher amp fuse to replace a lower amp fuse as you found out. I accidently did this on a wire going to the rear window defrost relay and then proceded to foul the water further by connecting said wire to my trailers tail lights.........but fouled out once more by accidently connecting it to a gnd wire (duh) I had made for the trailer.........and got about a half mile to a mile from home before smelling the foul smell of wire burning. Bad hair day all in all. Fuse blew but the wire (green/black I think memory says) in the defrost relays plug was TOAST. Well not so much the wire but the plastic of the plug where that wire goes was Toast with cheeze melt. If I had the right fuse in place the wire and plug would not have melted. Lesson learned ...again.

Usually you would need a new headlight switch plus the short harness that connects to said plug to fix the problem permanetly. Just an opinion. Someone on this forum actually fixes the internal contacts of the swtich itself to fix the problem. No idea who right now.

 

So you're saying that new headlight switches sold by mazda don't have the same inherent defect that the original ones that came with S4s have?