C101

[NC325iC]

So i took some time to search through 3 ETM's for a decent C101 Pinout and here is what i came up with, if anyone can fill in the blanks that would be great, any added knowledge would be helpful.

Formatted as follows

Pin#. Function - Engine side color, Body side color - basic function (notes)
if the wire is the same color on both sides there is only 1 color listed

1990+ 325i
1. Charge - Bu - ?
2. oil level - gn/yl, bu/bk - signal
3. .
4. coolant temp - br/vi - signal
5. oil pres - br/gn, bk/br - signal
6. oxy heat - gn/wt, gn/yl - +12v
7. ignition coil - gn - +12v
8. fuel rate (econo)- wt/bk, yl/wt - signal
9. tach signal - bk - signal
10. oil level - bu, vi/gn - signal
11. inspection reset - wt/gn, wt/bu - signal
12. check engine - gy, br/bk - signal
13. fuel relay - gn/vi, vi/red - +12v
14. speed - bk/wt, bu/yl - signal (from instruments to ECU from cluster C2 Pin 10 bu/yl)
15. unloader - bk/gn - signal
16. srs - wt/bkv -not used
17. ABS Communication - bk/yl - signal (325ix only)
18. starter - bk/yl - +12v
19. .
20. ABS power - rd/yl - +12v

1988-89 325i
1. Charge - Bu - ?
2. oil level - gn/yl, bu/bk - signal
3. .
4. coolant temp - br/vi - signal
5. oil pres - br/gn, bk/br - signal
6. oxy heat - gn/wt, gn/yl - +12v
7. ignition coil - gn - +12v
8. fuel rate (econo)- wt/bk, yl/wt - signal
9. tach signal - bk - signal
10. oil level - bu, vi/gn - signal
11. inspection reset - wt/gn, wt/bu - signal
12. check engine - gy, br/bk - signal
13. fuel relay - gn/vi, vi/red - +12v
14. speed - bk/wt, bu/yl - signal (from instruments to ECU from cluster C2 Pin 10 bu/yl)
15. unloader - bk/gn - signal
16. srs - wt/bkv -not used
17. ABS Communication - bk/yl - signal (325ix only)
18. starter - bk/yl - +12v
19. .
20. .

1987 325i
1. Charge - Bu - ?
2. oil level - bu/wt, bu/yl - signal
3. .
4. coolant temp - br/wt, br/vi - signal
5. oil pres - br/gn, bk/br - signal
6. oxy heat - gn/wt, gn/yl - +12v
7. ignition coil - gn - +12v
8. .
9. .
10. oil level - bu/yl, vi/gn - signal
11. inspection reset - wt/bu - signal
12. check engine - br, br/bk - signal
13. fuel relay - gn/vi - +12v
14. speed - bk/wt, bu/yl - signal (from instruments to ECU from cluster C2 Pin 10 bu/yl)
15. .
16. srs - wt/bkv -not used
17. .
18. starter - bk/yl - +12v
19. .
20. .

1986 325
1. charge - bu - ?
2. oil level - bu/vi, bu/yl - signal
3. .
4. coolant temp - br/vi - signal
5. oil pres - br/gn, bk/br - signal
6. Idle control - gn/yl - +12v
7. ignition coil - gn - +12v
8. .
9. .
10. oil level - bu/wt, vi/gn - signal
11. inspection reset - wt/bu - signal
12. .
13. fuel relay - gn/vi, vi/rd +12
14. .
15. .
16. srs - wt/bk - not used
17. .
18. starter - bk/yl - +12v
19. .
20. .

Tach signal - C104 Pin 1
Fuel Rate - C104 Pin 3
Speed - Instrument cluster C3 Pin 26 br/rd?

1985 325e (square)
1. Charge - bu - ?
2. oil level - bu/vi, bu/yl - signal
3. .
4. Coolant temp - br/vi - signal
5. .
6. Idle - gn/yl - +12v
7. Fuel Pump - gn/vi , vi/rd - +12v
8. Starter - bk/yl - +12v
9. .
10. Ignition Coil - gn - +12v
11. .
12. .
13. .
14. .
15. Oil Level - bu/wt - signal
16. Oil Pres - br/gn, bk/br - signal
17. Inspection Reset - wt/bu - signal

Tach - C104 Pin 1
Fuel Rate - C104 Pin 3


+12v means that when the car is running there will be 12v on that wire
signal can mean a variety of things whether its grounded when the switch is activated or it puts out an actual signal

[nando]

1990+ 325i/ix:
20 - rd/yl - ABS power (from main relay)

325ix:
17 - bk/yl - ABS communication

M3:
19 - Oil temperature gauge

[NC325iC]

so for the ones that arent occupied are they just empty pins?

Im wondering where the story of the +12v to a grounded wire comes from on the motronic 1.3 swap cause i dont see an issue with me using my '89 harness on my '86 based on the ETM diagrams

does the eta check engine signal run through the C101, cause its not shown in the ETM

[NC325iC]

I may as well include some explanation here, im wiring in an engine from an 89 into an 86. I know its been done before and i know its probably be explained but after reading x many threads where people try to explain it i still cant get the info i need, so...

since the 86 has the C104 connector in the glove box i will not need the tach and econo signal to go through the C101 but through the C104, as this connector is in the glove box it makes the most sense to pull it from the motronic connector, so:

Tach signal - Motronic Pin#6 (bk) connect to C104 Pin 1
Econo signal - Motronic Pin #32 (wt/bk) connect to C104 Pin 3

[nando]

so for the ones that arent occupied are they just empty pins?

Im wondering where the story of the +12v to a grounded wire comes from on the motronic 1.3 swap cause i dont see an issue with me using my '89 harness on my '86 based on the ETM diagrams

does the eta check engine signal run through the C101, cause its not shown in the ETM

yes, pin 3 is never used, and 17 and 19 are only ix/M3. the+12v/ground issue is pin 20. on early cars with ABS relays it's a ground (I think), on late cars without ABS relays it's +12v. 89's have ABS relays so it's not an issue, I think it changed in 1990 or possibly 91 (wouldn't be too hard to check in the ETM).

[NC325iC]

C104 Pinout for pre 88 models

1 - tach
2 - +12v from OBC Relay or Main Relay
3 - fuel

[NC325iC]

yes, pin 3 is never used, and 17 and 19 are only ix/M3. the+12v/ground issue is pin 20. on early cars with ABS relays it's a ground (I think), on late cars without ABS relays it's +12v. 89's have ABS relays so it's not an issue, I think it changed in 1990 or possibly 91 (wouldn't be too hard to check in the ETM).

Cant find any mention of pin 20 in any of the ones ive looked at except for 1991 where it is +12v from the main relay to the ABS hydraulic unit.

I guess ill snip it just to be safe.

[nando]

it would only matter for you if one of your harnesses was from a late car (I believe it's 1990 production, so 1991 MY).

[NC325iC]

You sir are correct pin 20 on this harness that i have (which is unknown model year actually) is empty so nothing to see here

[NC325iC]

my 86 body side has 11 occupied pins so i guess my pinout for the 86 is correct

[NC325iC]

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

[nando]

I don't know for sure - but it's just one wire, why not hook it up?

E36 ECUs go into limp mode without a speed signal.. no idea how the E30 ECU is affected.

[NC325iC]

alright so here it is in short

Swapping in a pre '91 engine harness into an '86 with round C101 is as easy as hooking it up and making 3 connections in the glovebox.

1) Tach signal - Motronic Pin#6 (bk) connect to C104 Pin 1 (gn or gn/bk)
2) Econo signal - Motronic Pin #32 (wt/bk) connect to C104 Pin 3 (wt)
3) Speed signal - this one is a little more involved, run a wire from the back of the cluster connector C3 (yellow) Pin 26 (br/rd) or C6 (green) Pin 1 (bu/yl) to Motronic Pin #29 (bk/wt) for speed input to ECU

other than that for this specific application there should be no other problems.

For a 91+ harness (with C101 Pin 20 occupied) the wire for pin 20 should be clipped just to be safe, in addition to the 3 wires above

the only thing that i have not answered yet is the Check Engine Light which with this current wiring setup will not be functional, it will probably require running another wire from the cluster to the glovebox

[nando]

do early cars have a CEL? I guess they must, but the diagnostics is pretty rudimentary.

[NC325iC]

I donno, hadn't thought about that. It wasn't shown in the ETM even in the cluster section. Maybe I'll put in a little light in the glove box or something.