CD Box Test / Starter Wires Hookup

I am in the finishing touches of a 1980SC restoration project that I bought in boxes and as this is my first porsche hope these questions aren't too stupid . In one of the boxes were 2 CD units , friends helping and even the local dealer suggested the obvious (put one in and if it doesn't start put the other one in ) but I can only guess that one is bad so they threw a good used one in the box . Is there some way/shop to test these units ? I read in an earlier post about a SCR trigger diode short ?
Also I have looked in all the books and on Pelicans motor drop pictures and cannot figure out where thick yellow/thin yellow-blue line wires hookup on the starter-solenoid ( spade terminals oriented top/bottom )? Again the obvious was suggested (if it doesn't turn over reverse the wires) dooh ! There must be a better way .
Thanks in advance and by the way this is a great forum some of my really simple questions were already answered .
Mike

Mike, I have a 1978 911 SC. If the CD system is the same on your vehicle I can give you the terminal Number and what it goes to:

31/1 - Ground on Vehicle
TD - Tachometer
31 d - To Distributor Pulse Generator
A - Transformer plus (+)
15 - Term. 15
7 - To distributor pulse generator

You may be able to check the unit with an ohmmeter. Clip one probe to the box and check the terminals with the other probe. You should get either no reading or a high resistance reading with the exception of terminal 31/1 which is the ground terminal. If you get a zero (no resistance) to any other terminal than that indicates the box may be bad. Record the information and check the other box and compare. Good luck.

Thanks Stormcrow the test results from both cd units are reading identical with both 31/d terminals reading as a ground/dead short ? It may be the ground for the Distributor Pulse Generator ? Well almost time to try and start it , either they both work or .....
Your info should be posted on FAQ , very helpful I'll see if I can add to it thanks again . Mike