Loss of Speed Control

MattR wrote:
It turns out the brake light bulbs were not burned out but they were making poor contact. I rotated them until they made better contact and now my cruise control is working. Thank you everyone so much for all of your suggestions!

THat will do it .. yes. Glad I suggested checking the brake lights.

Folks so you knwo here is how it works

The Cruse control has wires connected to BOTH SIDES of the brake light switch It looks for 12 volts across these two wires.

IF 12 volts is present then
1: The brake light fuse is good
2: The brake light lamps are good
3: The brake light switch is OPEN (Pedal in the UP or released position)

When you "Touch" the brakes this switch closes and the 12 volts goes away. So the cruse control say "AH. he wants to slow down) and releases the throttle.

thanks for the post back. Learned something but will probably forget before I get a chance to apply it. :W

It turns out the brake light bulbs were not burned out but they were making poor contact. I rotated them until they made better contact and now my cruise control is working. Thank you everyone so much for all of your suggestions!

Check the "clock spring" under the steering wheel.

Look up this site for good cruise control information, wiring diagrams and parts lists. thorssell.net

Check your brake lights to see if they are stuck ON.. Beyond that it depends on how the speed control works, since there are two or 3 different systems and I only know one of 'em.. I will say no more till I know more.

By "the sensor on the brake", do you mean the pressure switch on the brake master cylinder? If not, check that, assuming you have it. There was a huge recall on many of them, involving the installation of an inline fuse to prevent fires should they corrode and fail (as they were on an always-hot circuit), so check that inline fuse too if you have it...and enquire about the recall if you don't. I'm not sure if '91 is included in the recall or not; I do know my '98 was and has the modified wiring harness.

I had that happen on a newer F250. it shot ***** while going down a slight long grade, as i recall the speedo also went out. i don't know about your year but this one had a sensor that plugged into the rear diffy that gave the input for the cruise and speedo. Changed it and all was sell.

alfredmay wrote:
Older Ford vehicles used manifold vacuum to operate cruise control. I used to tow with a Ford van and my buddy had a Ford class C. We both would lose cruise going up long grades. Look for a vacuum leak. I believe the vehicles also used a vacuum storage canister....... check that too.

Those sound like excellent ideas... if I had any idea how to do it :-)

The sudden and complete loss of the system makes me think that it isn't a vacuum leak from my understanding of how these things work (unless it was huge leak like a tube coming loose from a fitting). Nevertheless, I did look over any tube I thought could be part of the system as well as any canister I thought could be holding a vacuum... nothing obviously leaky. The speed control system stopped working while almost coasting downhill at 55mph or so, although there had been long grades prior to that.

Older Ford vehicles used manifold vacuum to operate cruise control. I used to tow with a Ford van and my buddy had a Ford class C. We both would lose cruise going up long grades. Look for a vacuum leak. I believe the vehicles also used a vacuum storage canister....... check that too.