So I stupidly left my DB9 outside in the rain for a prolonged period of time to 'store'. It's put a short somewhere in the headlight system and I can't figure it out. Here are the symptoms:

1) I can't get the primary headlights (outside ones) on at all except for in a very strange use case (more on this later).

2) When I turn the **** to ON (either side lights or full headlights position), the headlights won't come on but the side markers and rear (lic plate) lights illuminate. Also, the green indicator on the dash illuminates. Now this is where it gets wierd:

3) when I turn the **** OFF, the green indicator on the dash stays on green. The side markers stay illuminated as well when in OFF position. They just don't turn off. In fact, even when I turn the car off and turn off all the lights, the green indicator still is illuminated and so are the side/rear markers. They stay that way for ~minute and then they shut off.

4) Everytime I open a door or lock/unlock the car, this also triggers the green indicator on the dash and the exterior lights. And they can't be turned off except waiting the time, even with the switches in off position. The car must be off and doors closed (locked or unlocked) for a little bit of time before the green dash indicator and the exterior lights turn off. It NEVER turns off when the car is on and I'm driving around. The green indicator stays on and so do the side/rear lights the whole time while the car is on. No amount of time or turning the switches off while the car is on can get these off.

5) This is what leads me to believe that their is a short in the system: if I completely disconnect the battery and drain the car, #4 doesn't happen immediately when I open/close doors or unlock/lock the car (aka it won't turn on when I just open doors and then stay on without recourse but time). However, the minute I try to turn the lights **** to on, the green light/ext light problem gets locked into the car and it's like that from now on. So it seems like the system control is out of whack.

6) lastly, I mentioned that it's really hard to get the main (the 2 outside) headlights to work. Thus I've been using my high beams and they work fine (on/off). However, here's how I know the outside primary headlights work ok: if I have my high beams on WHILE the CAR is ON, and then I turn the car off with all the lights switches in the on position, as the car turns off power, the two outside headlights light up alone with the high beams. This is the only us case I've had where these lights actually turn on.

As you can see, I'm at a complete loss of how to proceed as I don't think any individual light is broken, but somehow the control system for the lights seems out of sync. Could a shorted out **** be the cause or something deeper?

Please, ideas!?!

 

What condition is your battery? Crazy things can happen with a weak battery !!

 

I wish. New battery and I know Astons have problems with weak batteries. Thx!

 

Sounds like you need to diagnose the Master Light switch, Dip/Main beam stalk light switch, CEM Module.

The CEM module sends power through fuse #46 to the Master light switch, for the telltale LED. The Master switch has a ground for the telltale LED and sends this ground as the request back to the CEM or High/Main beam stalk switch on steering (all dependent on master switch position selected).

To get your Dip lights to work, the Master switch needs to NOT send a ground signal on the "Lights OFF" nor "Sidelights" circuit. With no ground on those 2 circuits, the CEM module would then command Dip Beam lights by default. If Dip beam lights are selected as a position, the CEM will allow the High/Main Beams to stay on at all times if steering stalk switch is set to High/Main Beam "ON" Position. If the Master switch is NOT set to Lights On, then the High/Main Beams will only be able to command Flash-To-Pass..means you would need to hold the stalk switch in position to keep high/main beams on.

CEM is located in passenger foot area, Master switch at drivers knee near door, Main/High beam stalk on steering. Honestly.. if you want to diagnose this issue yourself, you would need to get hands on the wiring diagrams and just diagnose each section. It's not overly complicated and once you see how the system works, would be fairly easy to diagnose the issue of concern causing the symptoms.

FYI, if you've ever had the windscreen replaced or previous issues of water ingress through door/window area, might be wise to investigate the CEM for water presence. The CEM does NOT have fuses for the Dip beam position, so very easy to internally fry the CEM if that circuit shorted.

 

THANK YOU Chris. Just the reply I was looking for as the schematics are so complicated, I couldn't unravel but with this guidance, I think I can start troubleshooting! Will report back once I make progress next week :-)

 

Just to follow up, I took out the light switch itself and saw a short on the board itself! cleaned that off with a pin, alcohol and an x-acto knife, put it back together again and pulled it in! Totally works fine again and it was what you said (ground on the first position when it shouldn't)! thx guys