A Line Mechanic reports he installed an incorrect Emergency Locator Transmitter (ELT) on a B737 aircraft while completing the emergency equipment portion of a jobcard.

Narrative

My job was 'emergency equipment.' Part of my duties are included in the maintenance jobcard. The aircraft I worked this particular night was one of the older B737's in the fleet. As I was checking the FWD Emergency Locator Transmitter (ELT) located on the right side of the cabin; I found this ELT to be missing the hold-down tape for the antenna and the string wrap around it was loose and coming undone. I noticed that the jobcard had just been revised and these revisions were pertinent to the ELT. I read the revision to determine the Part Number (P/N) for a replacement ELT. From the information on the jobcard; it states to no longer use Locator XXX. There is a note on jobcard at Step 5.C.2; that indicates the use of Transmitter YYY. This is what I ordered from Stores and installed onto the B737 aircraft. When filling out the FAA-8130 serviceability tag; I thought the ELT I removed was a Locator XXX; and that is what I put on the FAA-8130 tag. I found out that I should have used a Locator ZZZ instead of Transmitter YYY during the company investigation.