Victim:
2004 Dakota 4X4 QC
4.7 v8 - AT

Problem:
Cruise control lights up on dash but won't set.

Tests To Date:
3rd brake light was burnt out - Replaced = No fix.
Clock spring removed & tested - 100% working order.
Cable from servo to TB in working order.

Brake light switch removed and checked for continuity - 100% working order...BUT...After reading this post and trying the tests, I think my switch is toast.
Link - Dakota cc will not...

TODAYS DISCOVERY:
A hole was found in the servo...Should this unit be sealed?

 

The hole is your likely problem. The actuator works by vacuum. With that hole it can't pull a vacuum.

 

I just disconnected the vacuum line to the servo and got a blast of released air. I take that as a good sign of no leak.

I bought a new switch, it's in way better condition than mine plus I wondered what the black lever on the side was. The instructions state it's an adjustment once the switch is installed. If the lever is moved it's time to pull the switch. Mine was moved...I'll post my findings after a test drive.

 

Haven't had a chance to test drive yet (repainting my front bumper valance) so in the meantime I checked for power to the servo. Still no power to the servo...Just wasted $30 on a new brake light switch.

If I jump the brake light switch #1 & #4 I get 12v to the servo. I can hear a click from inside the dash when I push the brake switch. I think it's a relay but Chiltons doesn't show one. Anyone have a clue where the relay could be? By me jumping the switch am I bypassing the relay?

Thanks.

 

There is a switch at your brake pedal that could be sticking or out. However when mine failed the dash light wouldn't work either.

 

Thanks but you must not have noticed I mentioned the brake switch multiple times in my posts.

It's not urgent that I have it. I hate being stumped and just would like to solve it.
Can anyone answer this regarding the brake lamp switch?
"Try jumping terminals 1 and 4 together and then see if you have power at the cruise control servo."4-V32 20YL/RD SPEED CONTROL SUPPLY


I get power to the servo when jumping so I know the wiring works. I bought a new switch and it didn't solve my issue.

 

At least in the earlier Gen 2's there are no relays in the system.

Does your 2004 have a brake interlock switch that you have to press to put it into gear? That would likely be the relay you hear clicking.

I still think you have a bad servo. Where did the "blast of released air" come from? The hose or the actuator? The valves in the servo would be closed with power off but there is a reservoir under the cowl for the vacuum supply. That's likely the "blast" you felt although in either case it should be air going in, not out. The power for the servo is from the PCM. Everything else is in the servo.

If you didn't have the "set" light then I'd be looking elsewhere.

Do you have a wiring diagram? I don't for '04 so am looking at an '01. Rockauto shows the same switch from '01 and '04 so we can assume the pinouts are the same.

I think you are using the wrong pins on the switch.

Pin #4 is from the PCM - the supply for the speed control servo - not to the servo. Pin #1 is the +12v for the brake lights. The '01 wiring diagram matches what you posted for the brake light switch.

What do you show for Pins 2 and 3? They both should be listed as "output." Pin #3 goes to the servo in '01. Pin 2 would be to the brake lights.

 

Yes thanks.

The blast came from the little hose to the servo...Good point. Regardless I'm not getting power to the servo at the blue wire with red tracer.
Servo plug pin #3-V30 20DB/RD BRAKE LAMP SWITCH OUTPUT.

I just did a continuity test on the blue wire with red tracer from the brake plug to the servo plug. It's not a faulty wire, I even cut it where it comes into the engine bay and the signal died. That confirms I found the correct b/r wire. I think it has to due with the brake plug pin 4-V32 20YL/RD SPEED CONTROL SUPPLY.

Correct, I should have used #3.

2-L50 14WT/TN BRAKE LAMP SWITCH OUTPUT
3-V30 20DB/RD BRAKE LAMP SWITCH OUTPUT
4-V32 20YL/RD SPEED CONTROL SUPPLY
5-Z2 18BK/LG GROUND
6-V40 20WT/PK BRAKE LAMP SWITCH SENSE

 

Was the truck running when you checked pin 3 at the servo? Did you have the cruise control enabled as well?

 

The ignition was in the run position.
No I did not turn on the CC...If that works I'll be happy but pissed at the same time.

I'll be right back.