Just got through building the MAX232 ALDL Interface and hooked it up to laptop with Moates software and nothing. I am using the cig lighter adapter to bring in power and ground to interface. Do I still need to ground the A Pin on ALDL? ALso, do I need the resistor between A & B? Right now the only wire I have going to the ALDL is to Pin M. Also, Radio Shack was out of the 2N3904 so the pack I got says BC547. Would this cause a problem?

 

Yes.
Possibly, are the BC547's NPN?

 

What is the purpose of grounding the A pin on the ALDL, isn't it a ground anyway? Also yes the package was Radio Shack Part# 276-1617 and it says NPN-Type Switching Transistors. It contained 15 different transistors with 3 or 4 of each number. 2N4401, PN4141, MPS6514, and BC547. I am going to try the other Shack tomorrow and see if they have the 2N3904's in stock.

 

Yes, pn A is ground, but it is ECM ground, you need to make sure you are getting a good connection to the ECM ground.

 

Got the 2N3904's from the Shack today and scrapped the MAX232 and built the two transistor interface. Works great!!