There are a couple different information threads for 1990 DSM engine harness but nothing for 91-94 DSM engine harness and nothing that was complete with all the information in one area. So here is a complete post on all the wiring you will need.
You can either cut the two CSM connectors and splice them directly to the DSM harness or you can make a jumper harness if you want like Chris sells.
These are the CSM side connectors you are going to splice the DSM connectors to. The larger one is C-19 and has 15 spots with pin 6 being empty from the factory. The smaller one is C-17 and has 4 spots. Most will have 4 wires (thick BY, thick BW, thin BW and a YG), but as you can see, the auto cars seem to only have 3 wires (missing the starter wire, BY).
These are the DSM side connectors you will be cutting and splicing to the CSM connectors. The top one is C-67, the lower left is C58 and the lower right is C-59.
Engine bay wiring
DSM C-58 = CSM C-19
1-LW = 10-LY
2-L = 9-L
3-BW
4-G
5-W = 4-W
6-LY
7-LB
8- EMPTY
9-YG = 8-YG -- not needed unless you want your brake fluid sensor to work
10-BR = 12-BR
11-LB = 11-LB
12-GW = 15-G
13-RL- BCK LGTS
14-R- NEUTRAL SW
15-YG = 5-YW
16-LO
17-LR
18- EMPTY
DSM C-67 = CSM C-19
6-Y = 3-Y
7-W = 2-W
13-RG = 13-YL
14-BR = 7-WG
DSM C-59
1-W
2-BY = CSM C-17- 3- BY THICK
3-L
4-YW = CSM C-19 - 14-YW
5-BW- THICK = CSM C-17 -1 - BW THK
6-BW- THIN = CSM C-17 -2- BW THIN
A/C wiring
This section below is for people who want AC with the swap. Here is what you will need to do with the wiring.
CSM 19 - pin 1- BY = CSM 17-pin 1- YG
This will bypass the refrigerant temp sensor located on the compressor. DSM compressors didn't come with them so I feel comfortable not hooking it up. If you don't feel comfortable doing it that way, you could use the emissions plug (4 wire plug for evap purge, etc) and borrow two wires to go to the temp sensor which would be on CSM plug A-22 pin 1 and 4.
The rest of this wiring will be on the underhood side, in the engine bay.
DSM connector A-08 - pin 2 - GW = CSM connector A-22 -pin 6 - G
This will provide your dual pressure switch input.
CSM connector A-22 - pin 2 -BW- needs to be grounded. It originally goes to the ECU which then grounds.
Here is a picture of the A-22 connector (the unplugged one, it is on all CSM engine harnesses, whether you have A/C factory or not) on the stock CSM engine harness. What I did was clip it and splice it into the DSM engine harness so that I could keep the A/C wiring harness 100% factory.
Here is where the A/C fusebox/harness will plug in near the driver headlight.
Here is the important part of the AC wiring diagram.
The arrows on the top of both diagrams point to the connection from the AC control unit to the dual pressure switch. The circled areas from the pressure switch to the clutch relay shows you the difference between the way the wires are run on the DSM vs the CSM (CSM is a lot simpler). The bottom arrow on the CSM diagram is just to point out the A-22 plug and the wire that needs to be grounded.
DSM a/c
CSM a/c
This is what a slightly cleaned up and reloomed dsm engine harness will look like with CSM connectors all wired in. I eliminated the defrost relay and an emissions plug (4 wire plug) sense I won't need either of those. I didn't take the time to shorten wires on this harness but you can definitely do that if you want.
Starter wiring
Here is the starter wiring diagram for CSM. As you can see, circled are the connectors you will need to use.
For the starter wiring, you need to run a wire from the BY wire on C17 to the engine bay and connect it to the single BY connector on the stock CSM starter harness. That will get your starter turning over.