Yesterday the bulb out idiot light came on when I hit the brakes.
OK maybe I had a dead brake light, I circled back to have my pal check for which bulb was out, then the idiot light was out...everything OK?

All was normal and today again I got the idiot light when hitting the brakes for a short time. The right directional triggered it only once, and then the idiot light went out.

Does this scenerio suggest anything? why would the bulb out sensor trigger then quit? do I have a ratty bulb maybe?

??? Bill

I had the same problem about a year ago, the 'bulb out' module had become defective. A fresh one from Erie Vo-Vo solved the problem imediately.

Most likely a poor contact at the bulb base. Remove the bulb holders and clean them until all of the corrosion is gone, including the bulb base.

The fog lights are the same as the brake lights, interchangeable if a brake bulb should burn out. If the brake lights are old, just spend the $3 at an autoparts store and replace them. Always replace the lights as a 'pair', not one at a time.

Klaus
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Always willing to listen, just not able to take direction.

Hi Klaus,

Thanks again for your steadfast support for us guys here in the peanut gallery.

My bulb out idiot light still comes on when I hit the brakes yet all the lights are working including the center light over the back seat. Then the idiot light goes out. I haven't found time to service the brake light sockets, but wonder
what gives with the three lights in the brake light circuit? Does the bulb out sensor compare the center brake light or am I just looking for an imbalance with the right and left bulb? I don't have the luxury of owning a greenbook for the 850. (The one for the 740 is priceless for troubleshooting)

Bill

There is no green book for the 850 and newer cars.

The bulb out for the brakes is between the two sides. The center has its own wiring to the bulb out switch. Just clean the bulb contacts when you get a chance.

Klaus
--
Always willing to listen, just not able to take direction.

Dirty or loose contacts or bulb nearing the end of it's life. Current for both brake lights goes through the "bulb out" relay. It works when the current drawn by both lamps is equal. It's a reed switch held between contacts by a magnetic field created on either side of the "reed". If the current is zero on one side as when a lamp is burned out or loose, the reed is pulled to a contact and your dash light goes on. If you replace a lamp with an incorrect type with a different resistance, the current is always unbalanced and the dash light will go on, even if both brake lights work.

If you have a bulb about to fail due to a compromised filament, the current can be affected and the dash light might be triggered.

My wife's 940 is doing this now and it's either a loose socket or other intermittent. If I smack the brake light housing it comes on and the dash light goes out. Next on my list.

Erwin

Thanks Irwin,

Thanks for the reply, and I understand how the Bulb out sensor works.
It's just a puzzlement why the bulb out light is triggering without any dead bulbs.
I'll bet Klaus is right and one of the sockets /connections has corroded and become resistive causing the unbalance.
Tomorrow I'll check out the contacts.

Bill