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Cruise Control, Tach wiring:

(contributed by Laurence Chapman, Buggy222)

HUGE Thanks to Laurence for putting together the writeup on this!!

I have connected cruise control on my GTM. I did not want to have a non working stalk on the steering column. This is in no way a criticism of the FFR instructions or process. They aimed to get us a straightforward build as soon as possible and I am sure none of us would have wanted to wait any longer to get started.

I just want to share what I have found for the benefit of the other builders out there, I will document below what I had to do to get cruise control working.

The work falls into 3 areas.
1) Connecting the stalk to the correct pins at the fusebox or round plugs on the engine harness
2) Setting up the cruise disengage wiring and switches.
3 Making sure that the PCM is getting a Vehicle Speed Signal so it will engage, and knows what speed to maintain.

I have mine working, and had provided instructions to Pete Dove, who has confirmed that his is working also. My donor was 2001, his is a 2003 harness, but from what I can find, the cruise control function is the same from year to year.

The wire colors should match from one end to the other, so I suggest you find matching wire in the donor harness and keep the wire color consistent from origin to destination.

1) Connecting the stalk . 4 wires in their own plug at the steering column.
Cruise ON/OFF Grey wire to fusebox connector C2 - pin C4. (C2 is the middle plug on the fusebox). 12V when cruise in ON.
Cruise control set/coast. Dark blue to fusebox C2 - pin A4. 12V when cruise is ON and button is pressed.
Cruise resume/accel Grey/Black to fusebox C2 - pin B4. 12V when cruise is ON and button is pressed.
Battery positive feed. Pink to an ignition source. The painless harness has a cruise control wire you can use. It is pink 957.

2) Setting up cruise disengage wiring and switches

From the donor harness, there was a second switch at the brake pedal, which went in the hole above the location FFR describes for the brake light switch. This switch is used to disengage cruise control when the brake is applied. It may have had one or two plugs in it, but you want the plug closest to the brake pedal. This has 4 wires. You only connect 2 of them.

The purple wire goes to fusebox C2 pin B6.
The pink wire next to it needs 12V ignition source so you can use the same source as you used for the cruise control stalk. The purple wire should have 12 volts when the brake is not pressed, and drop to zero when pressed.

You need a similar set up to disengage cruise control when the clutch is pressed. If your donor was a manual, you should have the correct switch. If not, you will need to acquire this switch.

You will have to add a bracket to locate this switch in the same way the brake switches are located.

This plug has two wires.
The pink wire needs a 12v source.
The grey wire goes to C150, pin S. See below for help in locating C150. There are two grey wires next to each other at this plug. You want the one next to the black wire. This wire should have 12v when the clutch pedal is not pressed.

The regular brake switch has 3 wires (pink, white and light blue). The light blue wire is used by the PCM to check continuity in the brake light circuit. I don't think you actually need it for cruise control to work, but you do need it for ABS, and you might get a trouble code without it, so I connected it anyway. It goes to fusebox C2 pin F1. You will find that when you have no bulb in your stoplight, this wire carries about 4 volts, which is the PCM checking continuity.

3) Making sure that the PCM is getting a Vehicle Speed Signal
The FFR instructions have you splitting the VSS yellow wire, and using a white (alternator) and a green (power antenna) wire from the painless harness. I found that although the green wire gets the signal to the speedo, the white return wire did not get the right signal back to the PCM, so the PCM did not actually have the Vehicle Speed Signal.

There is actually a Vehicle Speed Signal wire at both of the round connectors. I used Connector C150 (the orange tape plug), pin L. This is the dark green/white wire next to pin M that FFR uses for the OBD signal. See below for pin positions, there are a number of dark green/white wires, so take care to get the correct one. On Connector C142 (blue tape) it is pin E (green/white also). Use either one.

You can leave the yellow VSS wire alone, and pick up the signal using this green/white wire. I ran it to the speedo on the green power antenna wire. The green/white VSS signal is the one that used to run to your donor's instrument panel. It pulses to ground, so it need a 12V source (with a resistor). I used any 12v ignition source, through a radio shack 5K resistor (but anything greater than 1K will work), and connected that to the green/white wire so there was 12v available to be pulsed to ground. Now connect your speedo signal to the green/white wire, after the resistor, so that the speedo can sense the pulse to ground, but is not getting the full (un-resistored) 12V. The resistor only needs to be 1/4 watt or more.

That is it!! Happy cruising - Laurence.

P. S. When I ran mine to test cruise control on engine stands it seemed to engage, then accelerate and then disengage. The manual says that if it senses too much acceleration while trying to control speed it will shut off. So road test it before concluding that you did something wrong.

As an aside, the method just described to connect the VSS signal to the speedo can also be used to connect the Engine Speed Signal to the tachometer, and avoid the use of the Tach adapter. The ESS signal can be found at fusebox C2 pin A3.

For reference, this is what is at C150 on my harness.

A Red/black A/c Pressure signal
B Grey 5v reference
C Black A/c pressure ground
D Orange/black Traction control signal
E Tan/black. Traction control
F-K not used
L Dark green/white VSS
M Dark green Serial data signal
N Dark green/white A/c request signal
P Dark green/white Engine oil temp input
R Black Ground
S Grey cruise control release signal from clutch
T Grey extended brake travel signal

From Pete Dove’s email:

Yes I decided not to go the route of taking a signal off the coils through the tach adaptor. Instead I hooked into the white wire - engine speed signal (circuit 121). You can hook into it at the PCM Connector C2 Position 10 or you can hook into it at the fuse box Connector C2 Position A3. Now you also have to connect a positive 12 volt wire with a 3.3k ohms resistor (minimum) in line with the 12 volt wire where it connects to the white wire. The white wire is then connected to the signal terminal of the tach. It will definitely work. If you want to stick with the tach adaptor approach you need to be sure that you are connecting both left and right coil banks through the adaptor. The instructions as provided by FFR were wrong (at least for 2003). They said that you need to cut pink wires in A6 and F2 in FB Connector C1. For 2003 the wires you need are A6 and E2. F2 is a injector wire which caused my engine start problem. You need to check for your year, but just remember you will need the left and right bank coil wires. The other thing I believe that you need to switch the tach for 4 cylinder operation (because the signals are coming from the coil banks in parallel - in other words working like a 4 banger). There are two tiny black switches that can be reached through one of the panel light holes in the back of the tach. See GAJC post above on how to set switches.

Chris, I-Squared
Pin 10 of the PCM delivers tach information. You don't need a tach adapter for this application. As Henry references; The drive circuit from the PCM is called "Open Collector" that means that it needs a resistive load tied to 12 volts to make the Collector of the transistor to do it's job. Our addition to the comment above is that the + 12 volt source for the resistor should only be energized when the ignition key is on.

The Ohm rating on the resistor is a fuction of what the Tach needs for a signal. Typically only a few milliamps at 12 volts (nominal). A 3.3k Ohm resistor will deliver 4 milliamps at 13.8 volts (what your care really runs at when the alternator is functioning). That value will keep the PCM happy and not stress the circuit. Use a 1/2 watt resistor for mechnical reasons... Just for clarification the circuit is as follows...

(Switched +12)---(resistor)---(Pin 10 of PCM). It can all be wired with 22 gauge wire...

Tach attaches to the junction between the resistor and pin 10


Note that for this to work you must set the tach for 4 cyl. There are two tiny dip-switches inside to the left of the hole for bulb access. You need to access them through this same hole and move them both down. I hooked up the resistor at the back of the gage, crimping it togeter withe spade terminals for signal and power wires.

From GTM4

A lil more detial on our set-up

There are two switches on the bracket that FFR supplied. One is for brake light and cruise disengage from the brake pedal movement. The other is for cruise disengage from clutch pedal movement. Both operate on the initial movement of the pedal.

There is a further OEM switch that can be mounted on the footbox, which operated only when the clutch is fully depressed. This is the starter engage switch. The circuit is complete when the switch is depressed. It can be used to operate a relay and connect the purple starter wire


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