Dubai944

I am currently rewiring my race car and removing the factory central electric box. The ABS is the one system I was concerned about rewiring incorrectly so I have kept the factory wiring in tact and seperated the relay from the fuse box. Power, ground and a trigger from the stop light circuit is all I need to rewire the relay in it's new location.

I have seperated all the ABS wiring wth the exception of one wire, the Black/Grey wire that runs from Pin 15 on the ABS Control Unit to D45 on the central box, and I can't figure out what this wire does from the wiring diagrams, so I am not sure what it needs to connect to when I seperate it. The pics below should explain what I am looking at. Can anyone help?

Van

What is M67?

Dubai944

M67 takes you to the detail for D44 which runs back to the alarm control unit in one direction (I doubt that is relevant). In the other direction D45 & D44 are joined and connect on to D+ [H43] which I think is the important link. I'm still trying to figure out what D+ [H43] is. I'm not sure how to read that and where that takes me in the wiring diagrams.

Dubai944

Does anyone have a pin diagram for the ABS Control Unit that identifies what pin 15 is?

Yarf

Look at the instrument cluster wiring for the M46 +D input, Maybe ABS warning light?
what model and year is your car.

Dubai944

1990 S2

The ABS warning light comes from Pin 29 on the ABS Control Unit via a white wire which I have already identified.

Yarf

H43 D+ shows Alternator D+/61 with a back reference to J69 D+. This could be a safety issue, if the Alternator is not outputting then the ABS is inhibited. This is only a guess on my part.

Dubai944

Yarf, thanks for pointing that out.

So if the wire at D+/61 on the alternator is 12V from the ignition, then the join at the central box is just a junction for 12V from the ignition to various units including the ABS Control Unit and the alarm control unit.

I wonder why the ABS control unit also needs a permanent 12V feed from the ignition.....it gets power from the relay every time the brake lights are switched? Interesting.

So in theory I should be able to supply the black/grey wire with 12V from the ignition and hopefully the ABS will be happy. Either that, or it will blow up the control unit

Yarf

It looks like D+/61 is a unique alternator regulator output that is used by the ABS, Alarm and Alternator Charging Indicator, there may more I have looked at all the possible connections. You should probably maintain this connection it may be part of some fail safe logic. But this is only a guess on my part.
Good luck.

Julian Allen

Pin 15 gets power from the alternator (D+, the small blue wire terminal off the alternator)--it's telling the ABS brain the engine is running. I guess the logic is, no alternator power, no running engine . . . no running engine, no need for ABS. In the test plan there is a specific test which shows the (test) LED lighting with the engine off, then extinguishing when the engine is started (with a note sometimes the throttle has to move first!). Like Keith said, the other use for this "alternator sense lead" the the warning light for the alternator.

Dubai944

Got it. Thanks for the help guys.

Dubai944

Resurrecting an old thread, but I finally got around to completing my rewire with the exception of the ABS.

Previously established that the ABS input at pin 15 connects to the alternator D+ circuit (charge warning light) in the factory wiring. The reason being for the ABS to know if the engine is running or not for some purpose.

I have since read elsewhere that some ABS systems are prone to generate low voltage faults if they do their start up logic check while the engine is cranking, so starting the ABS with a relay triggered from D+ delays the ABS system startup until after the engine is running avoiding the problem. I presume this is how this system works also.

So it seemed simple to connect the ABS pin 15 wire to the D+ circuit, but then I thought about the D+ circuit (which in my new wiring is simply from the alternator to the battery via a charge light as shown below). As I understand it the idea is the light comes on when there is no output at D+ (engine off or alternator faulty) and goes off when the engine is running and D+ outputs a balancing voltage to the battery voltage. I also understand that the alternator monitors the load at D+ to regulate output to the battery. All good.

Then I started thinking what happens if you connect an external circuit like the ABS input? Doesn't this screw up the load balance between the alternator and the battery by providing an alternate ground? Probably overthinking this but now I am completely confused. Where in my simple alternator D+ circuit should I connect my ABS wire??

Julian Allen

I think you put the ABS first, then a diode between every other place you use it (I have only used it as an alternator warning light). The diodes keep any current from back feeding the ABS brain.

Rokket

http://www.dropshots.com/SteveA#date...06-06/22:06:11

I was removing my AC/ heater box from my 944TS race car. I cut a few of the wires off but apparently damaged-cut the ABS Harness in the process.

I can't get the ABS light to come on when I pull the manual ABS kill switch (Worked before AC removal) and it appears that one of the white wires from terminal #29 on the control unit is shorted out between the 4-pin harness and the ABS Hydraulic unit.

So, I am going to remove & Isolate the entire ABS from the main harness. My dilemma is trying to figure out what "KL 15" and "KL 50" are in the ABS diagram in the Central Electric Board, and where to pick up the Stop Light signal.

I will run a new lead to the ABS Light (white wire term #14) in (the Instrument Cluster) because I have an open circuit between white wire #29 on ABS ECU and (Term #14).

Any Tips or Experiences would be helpful.


Rokket Horton,

Yarf

KL 15 is the ignition switch terminal 15 which is 12vdc with the key in the on position, relay G2 is activated by this signal and the relay is labeled G2 Term 15 on the electrical diagrams, G2 pin 87 is 12vdc when the key is in the on position. KL 50 is terminal 50 of the ignition switch which is 12vdc when the key is in the start position. KL50 is connected to the DME /ECU pin #4 and the solenoid on the starter.