Figuring out the Engine Harness

I spent a few hours looking at the engine wiring harness and all its connectors to see how I could effectively attach signals to drive dashboard lights and gauges. Bob Bath calls this the "snake," but I like to think of it more like a nine-headed Hydra.


Here's a photo (click to enlarge) of the wiring harness I removed from my Civic DX. I cut off the C118 connector because the wire to the sensor was too hard to remove. You're wiring harness may differ slightly. I figured out the connectors based on the description on page 23-16 in the Helms manual. That's my cat's tail in the upper right corner of the photo.

Important signals in main engine wiring harness:

• C104 blk/wht - "start" signal from ignition switch to activate the controller (through C124) (note: interlocked by clutch pedal)
• C108 yel/grn - coolant temperature sending signal to temperature gauge in dash (through C126)
• C110 yel and grn/blk - backup light switch (through C126)
• C112 yel/wht, yel/blu, blk - speedometer pulse signal (through C126)
• C118 yel/red - goes to oil indicator light on dash, pull to ground (through C126)
• C119 wht/blu - goes to battery indicator light on dash, pull to ground (through C126)
• T101 wht - High current alternator output that could come from DC-DC converter directly to fusebox and primary battery connection

Don't care connectors (can cut off, if desired):

• C101, C102, C103 - main ECU connectors
  
• C105 - coolant temp switch (to activate radiator fan)
  
• C106 - ignition coil (note: this is used in CivicWithACord, but T101 is suggested instead)
• C107 - TDC/CRANK/CYL sensors (to ECU)
• C109 - coolant temp sensor (to ECU)
• C111 - oxygen sensor (to ECU)
• C114, C115, C116, C117 - throttle position and other signals (to ECU)
• C120, C121, C122, C123 - fuel injectors (from ECU)
  

I think I'll hang onto the harness for a few more days before hacking it up in case I come up with any "bright ideas" for how I can use the "don't care" wiring to link items under the hood to the (now unused) ECU connectors in the passenger compartment.

Next up: thinking about the battery racks