Help identify this weird speedometer “thing”

[SSG_Karg]

I’m replacing the speedometer cable in my 72 Duster. Does anyone know what this weird thingy is that is is inline of the current cable. It has a single electrical wire coming out of it that has never been plugged into anything. I know I can omit it in the future and replace it with a one piece cable. I just wanted to see if anyone knows what the hell it is. Can’t find any reference to it in the FSM. It’s mounted to the inner fender apron below the master cylinder.

 

[RustyRatRod]

Looks to be part of some sort of cruise control. Factory or aftermarket, I don't know. But that appears to be a "universal" style bracket on it, so maybe aftermarket.

 

[nutz]

yes speed sensor ...seen after market like that
was that an option on that car

 

[SSG_Karg]

yes speed sensor ...seen after market like that
was that an option on that car

I have no way of knowing if it was factory installed or aftermarket. No build sheet. I’ve owned the car since ‘98 and it looked like it had been there forever even back then.

 

[nutz]

it dose look factory was that bracket bolted down
would the speedo cable reach without it
any signs of a switch mounted somewhere

 

[SSG_Karg]

it dose look factory was that bracket bolted down
would the speedo cable reach without it
any signs of a switch mounted somewhere

It was attached to the inner fender with 2 factory looking sheet metal bolts. The cable would screw together if you eliminate the cylinder because it has a male end and female end. No sign of any switch or even the female wire that it would plug into.

 

[nutz]

just thinking if its factory then the speedo cable wont reach the trans
maybe a speed warning
is it auto or man ...dose it have a seat belt warning light

 

[SSG_Karg]

just thinking if its factory then the speedo cable wont reach the trans
maybe a speed warning
is it auto or man ...dose it have a seat belt warning light

Originally an auto trans. No seatbelt light.

 

[townsend]

Emission control device used on some 72 models.
Go to chapter 25-7 in the 1972 factory service manual (automatic transmission) for more details.
Also look in the Chrysler parts catalog section 21-84-1, text page 21-5.
Part numbers:
2985875
3592372
2985878

 

[rbkt65]

also could be a emr light (emission reminder light or like cop cars have on them or an hour meter)

 

[SSG_Karg]

Looks like @townsend is absolutely correct.

FSM states that it was part of an emissions control system installed on vehicles sold in California.

 

[nutz]

what dose it do retard timing when hot and at a certain speed ..

 

[67Dart273]

If you don't have emissions cert in your state, and are not meticulous about "restoration correct" I would yard it out and use a 1 piece cable.

 

[SSG_Karg]

what dose it do retard timing when hot and at a certain speed ..

The way I understand it from reading the FSM, essentially it prevents the distributor from adding vacuum advance at a certain engine temperature and road speed. The speed sensor was plugged in to a control module that included a temperature sensor. The “package” included a 185* thermostat and a special camshaft that had increased overlap.

 

[nutz]

The first computer control dist.
Im sure 90% were tossed in the first five years