I looked this one up at the Essig Museum (UC Berkeley). It was the only Ampedus in the collection with this color pattern. Also the ones in the collection were found in my area.

Thanks, Joyce. Would you say that the two small black spots near the base of the elytra are enough in themselves to distinguish this species? Is the roughly heart-shaped patch at the tip enough by itself? Or is it necessary to have these two characters in combination? Is the small white spot at the neck a distinguishing mark also? Or maybe it's just reflected light? Is the reddish-orange color variable or even important? Without access to a collection for comparison purposes, I and other people wouldn't know which character(s) might possibly be shared by other species.
The Guide page for this species is currently blank, and I'd like to add a text description that's particular enough to allow anyone to differentiate future images of A. cordifer from all others.

The two small black spots at the base of the elytra and the heart-shaped black patch near the tip, along with the reddish-brown and black coloring, are unique characteristics in terms of what is in the Essig collection. Some of black spots are very faint in some specimens. A few other Ampedus species are missing the black spots but have similar patches on the elytra tips, but with slightly different variations in shape. The white marks on my photo are light reflections.

I always look at localities when I'm looking at specimens because it's another way of verifying the ID. Sometimes there are two or more species that look alike (without dissection). If something that looks like my insect hasn't been found in my area, then I probably have the wrong species. In this case, Ampedus cordifer occurs in my area, and there isn't anything at Essig that occurs anywhere else that looks like the beetle in the photo.

However, the Essig museum doesn't have all Ampedus in North America. It mostly has species from California and western U.S.. So I don't know if the Ampedus cordifer characteristics I mention are unique among all Ampedus in the U.S.. For that you have to ask an Elaterid expert.

Thanks again Joyce. I added some info to the species page.