I have a 70/71 half ton short bed six cylinder. in the speedometer cable there is this part the cable screws in both ends and two wires run from it. it carrys a D0OF part number I trace the wires.part way there is a box under the dash about 2x3x1 1/2 black top cream sides in color and then a pad on the driver side door Jan about an.inch in diameter. all three pieces carry the D0OF prefix. any ideas??

 

I found one of those on a parts truck and after some lengthy discussion on another forum, it was concluded that it was part of an emissions device, can't remember sure what though. I think it's basically just a hall affect device that sends a square wave signal.

 

please explain hall device

 

'Hall' effect or sender is a signal generator akin to a trigger wheel and shutter as used the pertronix ignition set up... the trigger can be a light or a magnet.

 

It is a cruise control speed sensor. At one time your truck had add-on cruise control. After the D0OF on it there should be 9E731. The box under the dash is the cruise control module. It should have 9D843 on it.

 

oh,cool cruise control?? whats the pad that is,in the door jam?? it does not have a plunger or anything I can see. I have a 78 usual that,has,factory cruise but never knew it could be on the old ones.

 

It's the same sensor as used later for cruise control, but it is for emissions, same as the silver button thing in the door frame. That's a temp sensor. There is a module on the firewall that takes these inputs and plays with the ignition timing to help with emissions.

 

It's not for dealer installed Cruise Control, as it wasn't offered for these trucks.

It has something to do with emissions (electronic spark control). There's a parts catalog pic of the whole enchilada, but I haven't been able to find it yet.

D0AZ-9E731-A .. Speed Sensor / Obsolete ~ 1970/71: See parts catalog applications.

 

Hey Bill. One example is illustration section 120.1...page 7.

 

Geez Louise, why didn't I think to look under 12000? I looked in 7000, A7000, 9000 and found nada.

Here's this pic and another...

 

If my memory serves me right it only allows the vacuum advance to operate when the truck ls in high gear.

 

ok this truck has points in it did it used to be a transistor style ignition like on some of the 427 galaxies. and why are they on this truck and not others I have owned. sorry to ask so many questions but I love this odd stuff. now I have a 78 or 79 lariat 8)at appears to have factory cause. the controls are in the horn button bar

 

I think in 71 they were still using breaker points.

 

DuraSpark electronic ignition introduced in 1974, but not all vehicles came with it until 1976.