My friend bought a replacement trans for his 1999 Dodge Dakota. I never saw the car, but I guess it's a 46RE. Anyway, he told me the new trans (from a 1996 Dakota) got a speedometer connection, but the original trans on his 99 Dakota got no speedometer connection, he said it's taken from the rearend?!
Why is that? Does he has the wrong trans or is that maybe also a RH/RE difference?

Might find some help here;
http://dodgeram.org/tech/specs/Ramspecs.htm

Shouldn't matter, should it? If the '99 Dak is anything like the '01 Durango (which I have), the speed is picked up by a sensor which detects the motion of the "tone ring" attached to the ring gear on the rear end.

All he should need is a plug for the speedo cable on the trans. Or just get a plastic cap (like on A/C hoses) to place over the cable attach point on the speedo gear housing.
-Marq

'98 was the first year the speedo input is taken from the rear axle. I imagine the reason was to save money since the rear end had been sending speed data to the ABS for years so why not combine the two.

I agree with john Kunkle. It should be fine to put it in as long as it has the round plug (RE).