This is on my 2001 Blazer ZR2 :

My lights go crazy on a real dark and rainy day but only then , other than that all is fine with them ..
I ordered a new "Auto Sunlight Headlight Sensor" as none of the dealers had one in stock and it's not in yet , I am talking about the one in the the pass side speaker ..
Now I know this could also be a BCM problem but like I said it's only headlight related and only on real dark rainy days when going under trees and such that everything blinks on & off , the gauge lights come on & off and a friend told me my tail lights were doing it also ..
Hard to tell what the headlights are doing ( DRL ) as they are on while driving and when I was at a stop light and could see the reflection of them in another trucks tailgate they were staying on ...
On a sunny day I can drive right until dusk and then the lights will come on automatically with no problems when it gets dark enough so that's what makes me think it's a sensor problem on just the dark rainy days ,and I mean real dark ?
If it's a light rain with white clouds the auto lights will not come on ..
Can the BCM be tested and if it needs to be replaced are they expensive ?
I'm hoping it will just be a bad sensor ?

Thanks !

Zed

 

Does it only do it on rainy days? If so you might have a short.

 

Is it only on the auto setting.

 

I forgot to mention that when it does act up if I turn on the headlights manually I can still hear the BCM clicking and see some slight flickering in the gauge lights , if I throw a rag or magazine over the sensor in the dash the blinking goes away with the light switch turned on manually and no more clicking of the BCM , the rag over the sensor does the trick ?
It did do it the other day around 1:00 PM when it got real dark just before a thunderstorm but it did not rain yet ?
So far this has only happened twice this summer , once way back around the first of July and then again on this last weekend ...

Zed

 

I would say that since you can kind of fix the problem with the rag over the sensor that you have the right idea that the sensor is on the friz. Did you ever find out a price on them ?

 

The price of the sensor is $23.00 bucks ...

 

I would say that the automatic headlight relay has worn out, not the sensor. Or the wire from the BCM to that relay is chaffed or loose. The BCM usually has a 10 second delay before it will turn the headlights on and off.

 

~Update~

Well I got the new headlight sensor and as soon as I plugged it in the headlights & taillights all came on immediately so I drove around on a few not dark days but grey days waiting for the sun to come out and the AHL's never did go out , we had good sunny day and they still stayed on ...
I put in a new relay BTW ..
So I got fed up with this and did the AHL mod with a 1/4 watt 680 Ohm resistor and haven't had a problem since ....

Zed