Thursday, July 3, 2008

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

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