1996 F150 XLT
5.0 E40D
2WD

I have read every thread and piece of information I could find on this, on every Ford truck enthusiast website that exists (seemingly).

My father passed away last year and that is how I got this truck. I worked on the Cruise Control on it once before, because the servo was bound up, and we fixed that together. That is not the problem now.

Both tail lights and the third brake light function properly.
The horn functions properly.
No ABS or SRS lights are on after you start the truck.
The Master Cylinder brake switch has had the recall done and is a closed circuit at rest (although, I can't get it to open when I hit the brakes?)

I have also replaced the servo with one out of a 98 or 99 crown vic with no change.

I've tried following a couple of online wiring diagrams, but they aren't very intuitive and the pin-outs and descriptions are different for different years, and I can't figure out what I should be checking.

Based on that, I *think* that the clock spring is bad, since I do not get voltage to that pin when I hit the ON button on the steering wheel. However, since I don't have an SRS problem and the horn works fine - I am not so sure.

I would really love a definitive test or answer before I just start throwing money at it (the servo was 10$).

Any thoughts or opinions are appreciated.

 

I know Ford just sent out a massive recall on all the OBS '93 + trucks for a problem related to a fire hazard. I don't think they'll touch it since you modified it, but worth checking. Go to the ford dealership near you and have them look up vin or do it on Ford's website.

 

The OP already stated that recall has already been done: "The Master Cylinder brake switch has had the recall done"

That has been an on-going recall for years. I just received a letter from Ford again about that recall for a truck that already had the recall performed and it is long gone from my stable. Their record keeping sucks...

 

I seen that, I just remember seeing something about the actual unit under hood or wiring to/from. I'm not 100% sure what the latest recall is as mines a '92 and completely vacuum controlled and I beleive in '93 it went to electronically controlled with vacuum disable

 

You are correct. The electronic cruise control came out in 1993. The Brake Pressure Switch is located near the RABS hydraulic unit. The 1994 and later trucks have BPS on the master cylinder.

If the OP cannot see the ON switch supply voltage as stated then they should verify power is getting to the switch. If it is then the cause is most likely the clock spring.

But I am concerned the BPS power never drops when stepping on the brakes. The BPS is a safety in case the BOO switch is faulty. There may be more than one problem.

 

I am not sure that I was testing the switch right. I was just checking continuity on it, and it was good. I stepped on the brakes and there was still continuity, but the engine was off, so there was no brake-assist, and I'm not sure whether I was putting 5-10 lbs of pressure on it or not. I would think it was way more than that, but who knows. Also, I was alone, and had the wires stretched around while I was in the cab pressing on the brake.

Most importantly, I read that the switch would fail open.

How would I verify power getting to the switch? Wouldn't I have to pull the airbag and steering wheel to check that?

 

These diagrams may help you out:







Since the horn works I would say you are getting power to the speed control button assembly. Pin 6 of connector C219. The Speed Control functions leave on Pins 2 & 5. The tests in the Troubleshooting Hints will verify continuity back to the button assembly.





Power is always applied to the BPS, you cannot measure continuity unless you remove the fuse. Your meter acts as path to ground...

 

I was talking about the Speed Control Deactivation Switch on the end of the Master Cylinder. It is supposed to be the most common fault, according to my reading, but everything said it failed open.

I just disconnected the connector and checked the switch itself and it has continuity across the leads regardless of whether you are pressing the brakes or not.

So, either is has failed closed somehow (which shouldn't affect the operation of the cruise control), or you have to have the engine running - to get brake-assist to put enough pressure on it to open it.

Thanks for the diagrams, I'll try the resistance tests and see what I get there.

 

aka Brake Pressure Switch (BPS) in the diagram.

The Recall harness adds a smaller inline fuse to the BPS circuit. The membrane between the internal switch and the brake fluid is known to leak. Brake fluid is conductive. A 12VDC 15 Amp supply and conductive fluid create heat. Heat starts fires.

 

I have the recall - with a big harness and 2 inline fuses (both good, I checked them yesterday).

I will replace that anyway, cause it is old and decrepit looking and I've been replacing little things as I go and trying to get everything working right. That switch is cheap and easy, and I don't like that I can't get it to open.