hfbrooklyn:
... but my heat-shrink tubing is too small to fit over the connection.
If this was for a serious, long-term application, the obvious answer would be to go out and buy the correct heatshrink.
However, for a temporary rig at 12V, it will no doubt be just fine. The only significance of the amperage is the likelihood of the connections heating and melting the tape, in which case it will be very difficult to prevent failure short of constructing it properly. 
JohnLincoln:
If it was not suitable for insulating electrical joints, then it would not be called/sold as electrical tape!
You are kidding, are you not? 
Vinyl tape is not legally supposed to be used by electricians in any installation. Never mind what it is "sold as".