C101

[Jean]

early cars don't have a check engine light, so you just run one wire to control the bulb from the dme/harness. the other end for the bulb goes to switched power.

[NC325iC]

sounds good, thanks for the help nando and jean, hopefully this thread will answer questions for others

[Mike]

Vehicle speed is for cruise control correct? My 11/88 325i swapped to 5 speed does not have cruise control operating and want it working.

[nando]

I don't think so, the CC has it's own computer seperate from the ECU.

[NC325iC]

Instrument Cluster

Blue Connector is C1
White Connector is C2

I will take speed signal from the cruise control output, the green connector

there is a check engine light but i dont know what controls it i will likely snip the ground wire and run a new wire to the ECU

Is the ODOmeter driven by the speedometer signal?

[nando]

the odometer is driven by the speedo itself, which takes it's signal from the diff, and then outputs a separate conditioned signal for the CC, OBC, and ECU.

[NC325iC]

awesome thats what i was hoping, i just replaced the speedo in the cluster with a new one with good gears and correct(er) mileage. since the old odo didnt work i wasnt sure if it was hooked up (the cluster has been swapped to an i cluster previously)

[peete]

what does the ECU use the vehicle speed signal for? is it necessary for me to run that extra wire?

It's used for the service indicator, and maybe more. It will also show up when you plug in a Peake reset tool.

[NC325iC]

the service indicator is completely inside the Instrument cluster if im not mistaken.

[nando]

yeah, the speed signal is an output to the ECU, and there aren't any other communications to the cluster other than RPM and fuel rate.

[NigelStu]

Awesome - This is a huge help. I finished swapping the mechanicals this weekend (87es M/T to 'is' M/T using an 87is head/intake/etc and engine harness with 053 ecu from an A/T car), and after a no-start problem now have a headache from trying to find all of the C101/104 connections in the ETM.... It seems they forgot to add the C101 pin-out to that manual.

2 Clarification question
- does the C104 -> C101 splicing need to happen for the starter to crank and fuel pump to turn on? (I have not spliced in 104 yet, as I needed the info in this topic. And currently there is no voltage to ecu pin 27 with key on)
- are all '87MY C101 connectors that are round the same? I read up a bit on early to late models; updating a square C101 to round for proper swap, but both of mine are round. Also, pin 20 and 12 don't match - 'e' body side has a pin in 20 but not in 12, 'i' harness side has a pin in 12, but not in 20.

[NigelStu]

I've answered my own question for the C104 splicing, not necessary to make starter crank (but the starter signal wire does need to be plugged into the correct spade, the bottom one, not the top... doh!)

My second question still stands.

[TobyB]

Bump for big thanks-
there are more answers in here than I had questions...

and yet,
turns out I needed these answers!

You guys are the best <snif>

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