Help to identify He111 piece

[gedburke3]

Dear all,
I have a small part from the site of a Battle of Britain Heinkel crash.
Unfortunately I am unable to post a picture of it.
I am hoping that somebody will be able to identify the piece from my description and let me know whereabouts it would have been originally located on the aircraft.

It is 2.5cm wide and 7 cm long.
There is a rectangular aperture in the middle which is 2cm long and 0.5cm wide.
There is a round hole, presumably for a screw, at the top and bottom.
At the bottom of the aperture is the word EIN and below this a serial of numbers L3*817. (I can't confirm the digit marked as * due to damage).
At the top of the aperture there is the following: 0V.25A.

I feel that its most likely use is as part of an electrical component and presume that a switch would have been located in the aperture.

I would appreciate any assistance that you may be able to offer me.
Kind regards
Gerry