The "hood open" warning message popped up on my dash, even tho the hood is closed. The issue is that the wire carrying the ground to the sensor is not actually grounded. I need to find out where that ground connection occurs in order to diagnose further.... please help.

The issue is NOT in the switch itself. Ohming out the sensor shows that it correctly closes the circuit when the latch is "latched". (BTW, it was a PITA to get that latch/sensor out; expecting similar PITA to put it back.)

The issue is that the ground side of the wiring coming into the sensor (pin 1) is not, in fact, grounded. Manually grounding out the sense side of that connector (pin 2), successfully eliminates the "hood open" warning. And checking ohmic connection from the ground side of the connector to the chassis shows that it's floating.

This grounding wire quickly buries itself in the front harness and I can't seem to find where it's actually grounded to the chassis. The workshop manual is worthless, other than telling me that it goes directly from the hood sensor, through the harness and to a ground point (i.e. it doesn't go thru another connector).

I suspect it's bundled in what looks like a set of ground wires attached to the firewall behind the front fuse box. But before I tear that all apart, I'm hoping someone here has dealt with this and already done the painful work of locating. Thanks so much!

 

I know Aston’s can be “touchy” electrically, but it seems to me that ground is ground and there’s no need to be picky about which grounding wire is carrying ground to that sensor, which is just a simple switch (correct?) The fuses are on the +bat side. I’d just go ahead and ground it, either by tapping into an existing wire or running a new one.

 

Closing this one out: The issue was a mouse had decided to nibble on a section of the harness under the wheel liner.

Agree with @SloMoShun that I could have just found a local ground and tied into it. However, I'm always suspicious when something "weird" happens that there's a deeper problem. Glad I was suspicious.

In this case, I figured it was unlikely that the actual grounding point had gone bad (it's just a ring terminal tied to chassis somewhere -- and the car doesn't get driven enough to NVH it off that tie). So most likely was a harness issue. Figured out that the harness dives under the front right corner and is sandwiched between the right fender and fender liner. After removing the fender liner, found that a mouse had chewed up a portion of the harness. Not only was the hood sensor ground broken, but there was another small gauge wire broken and two other wires slightly compromised. Also, the mouse had decided to nibble on my front washer hose (didn't find out earlier b/c the wipers don't work when the car thinks the hood is open). So it was overall good to have traced it out and found the root.

BTW, to answer my own original post: the ground for the hood sensor (and MANY other engine bay components) is indeed on the right side firewall, behind the fusebox. There are four separate grounding terminals with 2-4 ground wires coming off of each one.