Guys,

What wire coming from the PCM is for the tach?

I'm working on an auto start for my truck and I'm not sure what wire to use for the tach signal.

The paperwork I have says pin #27 on the C2 connector, and it is grey/black.

None of the 3 plugs have a grey/black on pin 27.

I'm assuming C2 is the middle plug, but I can't find info on that for sure either.


I searched looked through the FSM... All 2900 pages of it, and no luck.

 

8w-30-39, lists the crank shaft sensor signal wire from ECM to PCM as an 18 ga. Grey w/Black wire. I imagine that would be a constant voltage signal since its from on computer to the next, not a pulsing voltage like that off of the sensor itself, but theres only one way to find out.

 

I found the pinout for the PCM in the FSM after I had posted that.

There is a grey/black wire that is marked at crankshaft position sensor.

As far as I know, the tach gets the signal from the CPS, so going to tap that wire and see what happens.

I read a bunch of info on the tach operation, but the fail to mention how it gets it's signal.

One interesting tidbit, the odometer only goes up to 499,999 and it will just lock in at that mileage. Wonder what you have to do then?

 

this is from directechs.com that we have at work...


Diesel tach wire is gray/black. The wire is located on the center of the firewall. There are two black plugs, the wire is in the top plug without the white insert

I used this location when i did my Remote starter on my truck... the wait to start light wire is up there as well but it is in the other plug! ... good luck!

i listed all the info below for a 98


Chris

Item Wire Color Polarity Wire Location
12 Volts red and pink/black + ignition harness
Starter yellow + ignition harness
Ignition dk. blue + ignition harness
Accessory black/orange + ignition harness
Second Accessory black/white + ignition harness
Power Lock orange/purple 5wi driver door harness
Keyless models use positive trigger for lock, and 5-wire for unlock. Can also find wires at the central timer module to the right side of the steering column, lock is orange/green, unlock is pink/green.

Power Unlock pink/purple 5wi driver door harness
Keyless models use positive trigger for lock, and 5-wire for unlock. Can also find wires at the central timer module to the right side of the steering column, lock is orange/green, unlock is pink/green.

Parking Lights (+) black/yellow + driver kick panel
Headlight lt. green/black + steering column
Left Front Door Trigger yellow - driver kick panel
To avoid dome delay, use tan for the drivers door and black/lt. blue for the passenger door. Both wires are located at the central timer module to the right side of the steering column. Use both wires and diode isolate each.

Factory Alarm Arm arms with lock
Must see a ground on the tan drivers door trigger wire while locking to arm the factory alarm. This only works if the vehicle does not have delayed domelight.

Factory Alarm Disarm lt. green/orange - driver kick, door harness
Tachometer black/gray ac ignition coil
Diesel tach wire is gray/black. The wire is located on the center of the firewall. There are two black plugs, the wire is in the top plug without the white insert. The tach wire can also be found at the ECM on the passenger side firewall in connector C-1, pin 8.

Wait to Start orange/black - center of firewall
There are two black plugs, the wire is in the top plug without the white insert. Also refer to DirectFax document 1090.

Brake Wire white/tan + brake pedal switch
Horn Trigger black/red - steering column
Wipers red/black and red/yellow + steering column
Left Front Window (Up/Down) lt. blue - white A driver window switch in door
Right Front Window (Up/Down) brown/white - purple/white A driver kick, door harness

 

Just for FYI, the wire for the crank signal is the correct one.