We look at this accident as being part of the insured's work, even though the third screen was not the focus at the time of the accident. As we see it from the description, the screens work together to form one image, with the image spreading across 3 screens. While they're separate TVs, they work together to create one picture. The wiring is part of the TVs, and he was working on the wiring in order for the TVs to function. The entire project was part of the insured's work.

While using the care, custody, control exclusion for property damage might be a stretch, the property damage to the third screen could fall under other portions of the property damage exclusion, such as in paragraphs (5) and (6), which state:

(5) That particular part of real property on which you or any contractors or subcontractors working directly or indirectly on your behalf are performing operations, if the "property damage" arises out of those operations; or

(6) That particular part of any property that must be restored, repaired or replaced because "your work" was incorrectly performed on it.

As for case law, we did find a duty to defend case with an underlying similar situation with glass/window frames:

Celina Mut. Ins. Co. v. Gallas, 2017 U.S. Dist. LEXIS 12166.  In this case, workers were instructed to clean window glass using a certain product, and in doing so got the product on the window frame and windowsill, causing damage. A suit was filed against the company for the damages. While the insurer at first agreed to defend with a reservation of rights letter, it later stated that it did not have the duty to defend because the policy did not apply to the loss as it was excluded under the "your product" "your work" exclusion.