I could use help identifying this little box with wires attached on the upper firewall of a 71 Challenger. It's on passenger side has mopar emblem and 3656 078 1602 on it. I hope I got the pic on here.

NOX...emissions

Yep - it's part of the NOX system that came on some cars

It's extra weight. I could get rid of it. Shine it up and sell it for big bucks! Thanks.

It measures the air temperature in the cowl and sends the info to a controller that retards the spark under certain conditions.

John -I thought your were BS-ing me. I bought the car from California. There is info in my shop manual under Cleaner Air System for California cars using thermal switch, vacuum switch, control module, solenoid vacuum valve. I never looked in this section before. Thanks, I'm learning once in a while ! The other pieces of the system are long gone, as well as the 318 that was in there originally. The plan will still probably be to get rid of this last piece of the NOX system. Very good.

One part of that NOX package is a speed switch mounted on the trans speedo connection, it provides a ground at 40 MPH....useful for OD conversions and other mods that are speed related.

Good information! That will be long gone on my car with any small block stuff that was original. It's a 440 car these days which is how I bought it. I was wondering about creative uses for some of the pieces in the NOX system. The temp switch might come in handy to keep a car running right, idling right , etc.

john, it's hard to tell from the pic [my old eyes], but is that the 7/8"x20 [?] speedometer cable thread on both ends ? what years were those used and do you have a part # ? also, are there other applications in other years and makes that uses a similar part ?

I've got one laying around I can measure the thread (and look for a part number on) if John doesn't chime in, but imagine he might before I get out to the garage this morning.

Yep, standard speedo threads at each end. I believe these were used in '71 and '72 only on cars with the NOX reduction package.

P/N is 3438494

Had a 71 Imperial that had that on it

thanks john ! now i can search for one. [seems i need another project just to make sure the ones i have don't get done !]

oz, what kind of wrench does your gizmo take at the transmission end ? it looks odd shaped, like you need a spanner type to tighten it to the speedometer gear housing ? or maybe it's my eyesight again ?

Just the angle of the picture, it is just a normal hex.