My F16 fuse keeps blowing, I checked around for a short but could not find anyting. Just out of curiosity I disconnected both back lights,control panel,dimmer switch and the fuse is still blowing. Could it be the switch itself? or is there something else that I'm missing.

and to my understanding the F16 fuse only controls the control panel lights and Right back lights? is this correct or could the be something else shorting F16 out. By the way i have never had this problem before and I did not mess or hit anything the fuse just blew on it's own.

 

I don't know the year we're talking about but it's possibly the Bulb Failure Warning Sensor. Large red relay on the driver's side.

 

sorry it's a 89 240DL, I somewhat solved the issue but never took into consideration the Warning sensor. I saw that in the manual what does that really do? and when it goes out what is a symptom?

thanks

 

The bulb failure relay detects when there is a burned out bulb and then turns on the warning light on in the dash. I have seen these short out and blow fuses.

If you pull the cover off the relay, see if it has an electrical burning smell, and look for burned circuitry.

Pull out the relay and see if the fuse blows.

If it blows still, you have a problem in the switch or wiring to the dash lights, or the wiring to the relay.

If it doesn't blow, the relay is bad, or the wiring to the rear lights.

That is my guess based on memory. I would need to see a wiring diagram to be certain.

B

 

when I first got my car I remembered that the light would come on telling me the light is out that I never saw it again, I do have two lights phsically out of there sockets but would that cause the relay not to show a bulb out error?

and what lights does that relay control?

 

What bulbs do you have out? The way the bulbs are laid out in your light assembly (parallel) theoretically would draw the same voltage when one is removed, but less amperage. What I believe may be happening (similar to fog lights) is that your removed bulbs are causing the others in the circuit to draw more current and blow the fuse as opposed to the bulb. You'll notice on some vehicles that when one fog light goes out then the other one gets much brighter and blows shortly thereafter. Keep in mind that when you have an electronic device with a specified load rating (ie 12v @ 3w) the device will operate at less or more that rating, and when you remove a load device earlier in the circuit, then the device will have more power to operate on, sometimes too much. Try putting those bulbs in and see if your fuse still blows, assuming they're on the same circuit.

No to clarify how your bulb failure sensor works: Several matched bulb circuits go through several reed sensors in your relay, like running lights R&L, brake lights R&L for example. Basically lights that are on on both sides of the car at the same time.

Power is fed into your relay to these individual circuits through a common 12v pin and divided amongst the circuits causing all the lights to shine. The right and left side for each bulb set has its own reed switch in the relay. When both bulbs draw the exact same current then the electromagnetic fields cancel each other out and the reed switch stays neutral. When one goes out, or you put a differently rated bulb in, then there is an electromagnetic field present in the coil and the reed switch is drawn to it magnetically, closing a circuit which causes your bulb failure indicator light on your dash to shine.

It is possible (and very common) to have a cracked or shorted solder within the relay. I have posted a bulletin "brake light issue fixed" that has a link to a place that will help you test your relay.

Good luck

 

you can get a 'short finder' off fleabay. It is basically a self reseting relay (flasher) and a compass each time the relay comes on the needle deflects. You follow the circuit till the needle stops deflecting and you have the location of the short. It will work through headliners, etc so you don't have to tear everything out.... Worth the money if you have a short......