It is the A & B terminals. You can jump them with a paperclip. Just make sure it doesn't touch any metal on the engine and ground out.

find the diagnostic connector right next to the computer jump terminals A+B (right next to each other) black/white and a white/black. set to 8 degrees and done

maybe someone could come over and do it for you. would that be ok

I have a suggestion, if you don't know how to do it and do not have a manual don't do it!

It is the Data connector in the stamped steel box on the pass side top of the motor. Unplug the cover on the data connector. It will have two rows of 4 I think. You will jump I believe AtoB but i also need to get the book out. I use a laptop or DDT to do timing. The proceedure is to run the motor @ 1600-1800 then jump the terminals to put it in base timing mode and set the timing to 8 BTDC. This is all off of memory. Let me get the book out in the AM unless someone beats me to it.

Short A and B on the data link connector(like the other guys said, can use a small paper clip) Your year should be a mefi 3 and once in "set timing mode" it should raise the rpm by itself. If it is mefi 1 you will have to raise the rpm manually, do not go above 1600 rpm, ~1200rpm is fine... and yes as previously stated...8 degrees btdc.

I looked it up in the service manual. the proceedure for using the merc timing tool (jumpimg A&B) is to jump A&B then run the engine to 1800 rpm's +or - 200 rpm, and set the timing to 8 deg BTDC, remove the jumper and return the throttle to idle.
It will not automatically run the idle speed up on the 502. You need to do it manually. In service mode the 7.4LMPI would automatically increase the idle. I was pretty close for memory but wanted to be sure so here it is. Good luck.