What is this?

[tucsonjwt]

I am in the process of reattaching everything under the dash and came across this. A yellow plastic box marked AC and a three wire harness coming out of it going to what appears to be a small light (?). Does anyone know what it is and where it attaches? I have an 83 C20. Thanks

[sweetk30]

look like the optical sensor for the back of the speedo for VSS input for cruise / or other functions .

if it has three wires ( red / ? / green ) on it i see in the back ground thats what i guess it is .

and it looks a little screwed up also like its been ground up . . . or could be the angle of the pic .

[SunSoaked]

Red/black/green wires. As k30 said, it's the optical sensor that attaches to the back of the speedo in guage clusters. Mine drove the cruise control, which I recently removed when I put the Vintage Air system in.

[tucsonjwt]

Thanks for the information. I see that the part number on the yellow module is AC 25007227 and may still be available as NOS, and it is called "sensor buffer." I do have cruise control and it works only intermittently, but I don't know if this module is ok or not. My sensor has no apparent physical damage, unless there is supposed to be something attached to the end of the black part, which looks like a small light or two?

Where does this actually connect to the back of the speedometer in the gauge cluster? Is the little light (?) in the black part supposed to attach to the speedometer at the instrument cluster somewhere? If so, where does it attach? The yellow module is just supported with a zip tie, and the black part is hanging loose under the dash. I did not notice this sensor when I removed the instrument cluster, and I did not notice anything on the speedometer gauge or speedometer cable that looked like it was missing anything.

[tucsonjwt]

The wires going to the yellow module appear to be black, pink, and yellow. The wires going to the black piece appear to be green, red and blue (or black?) The black piece has a different part number (25007166 2402 - made in Mexico.)

[tucsonjwt]

I found a listing for this part number online which states:

"Choose from Digital or Analog. Color is light green for analog Yellow for digital. Original GM AC Delco. 25007227 Digital dash unit. ( yellow ) 25007463 is for analog gauges ( green ) Part number 25007463 is for analog gauges. Part number 25007227 is for digital dashes and fits just about everything with digital dash."

I have analog gauges, so is this the wrong one? Did GM trucks ever have digital gauges?

[SunSoaked]

If I recall, all you will see is a hole (may not be round) that those lights see thru. That plug will be held in place with a small screw. It's like a reluctor ring, it's just measuring the rotational speed of a spinning disc (or whatever is in there?).

[SunSoaked]

The wire colors may vary slightly. Mines an 85. All my red wires look pink, black look brown, etc. Lol. That sensor uses photodiodes, just like a CD player.

[hatzie]

As has been said that's the Optical pickup for a VSS signal to the Cruise III Cruise Control. There should be a hole next to the speedo cable to insert that sensor on most 82 and later clusters.

The Yellow or Green box is a VSS buffer/amplifier. Not sure where Digital vs analog comes from. Yellow and Green do the same thing. The output signal is a square wave with a frequency of 0.556 Hertz/MPH.

Some of the cars used the signal for the early electronic fuel injection so the boards have two output connections. I believe the 87 and later trucks had a pass-through gear drive VSS in the transmission but don't quote me on that.

Download the Cruise III textbook from my manuals post. There's a bunch of info there. If your Cruise III is otherwise knackered good luck finding parts.

[tucsonjwt]

Thanks for the info. I notice that the cruise control manuals are through 1982, then start with another manual at 1984. The cruise control III does not show my particular cruise control stalk control (mine does not have the intermittent wiper control on the stalk.) Is there a separate manual for the 1983 cruise control only?

[tucsonjwt]

If the VSS must be connected to the speedo in order for the cruise control to work, then why does my cruise control sometimes work without being connected?

[tucsonjwt]

I am posting pics of the back of my speedo head. Can someone indicate where the VSS "bracket" to connect the VSS would attach? Should there be a bracket held down by the silver colored screw to the right of the rectangular window? Thanks.

[USSkoval]

That screw is not the original type, but that's what will mount your optical sensor to your speedo.

You said when your cruise works, it doesn't maintain speed if something like a hill causes the truck to lose speed. That's because the sensor hasn't been mounted up, so the truck doesn't know it's slowing down.

[hatzie]

Originally Posted by tucsonjwt

Thanks for the info. I notice that the cruise control manuals are through 1982, then start with another manual at 1984. The cruise control III does not show my particular cruise control stalk control (mine does not have the intermittent wiper control on the stalk.) Is there a separate manual for the 1983 cruise control only?

That textbook is what's available. They might've published one for 83 but I do not have a copy.
The wiper control has no bearing on the operation of the cruise control. IIRC the 1983 wiper switch is on the Dash. The set resume etcetera on the cruise control switch should operate the same as the later switches in the cruise III textbook.
The 1983 service manual probably has a section on cruise control. If the 83 system is very different from the 84 and later it will be extremely difficult to get parts for it.

[USSkoval]

I'm very curious now, what does the '83 cruise control stalk look like? Is it just a single SET button on the end like the older models, or was there also RESUME/ACCEL like the '84 and later multi-function switch?

[hatzie]

Originally Posted by USSkoval

I'm very curious now, what does the '83 cruise control stalk look like? Is it just a single SET button on the end like the older models, or was there also RESUME/ACCEL like the '84 and later multi-function switch?

83 is a transitional year for the interior controls.
If it's Cruise III with a column mounted dimmer the stalk should look just like the later ones without the wiper controls.
I don't have the wiring diagrams in front of me and I don't remember if the 83 dimmer is on the column or on the floor.
If the dimmer is not on the column the switch stalk probably looks like the late 70s very very early 80s Berlinetta Camaro with the last of the cruisemaster systems that had resume.
A picture would be darned intresting.

[USSkoval]

Originally Posted by hatzie

83 is a transitional year for the interior controls.
If it's Cruise III with a column mounted dimmer the stalk should look just like the later ones without the wiper controls.
I don't have the wiring diagrams in front of me and I don't remember if the 83 dimmer is on the column or on the floor.
If the dimmer is not on the column the switch stalk probably looks like the late 70s very very early 80s Berlinetta Camaro with the last of the cruisemaster systems that had resume.
A picture would be darned intresting.

'83 still had the floor dimmer for sure.

My '79 Camaro had cruise control, but the PO sold the turn signal stalk out of the car, so I don't know what that looks like either, lol.

[hatzie]

Originally Posted by USSkoval

'83 still had the floor dimmer for sure.

My '79 Camaro had cruise control, but the PO sold the turn signal stalk out of the car, so I don't know what that looks like either, lol.

Floor dimmer and dash wipers with Cruise III should likely look like Dakota Digital HND-3.
This is the stalk you use to do a clean retrofit of the T400 and 90's GM cars electromotor cruise control boxes or the better Rostra units into the 70's trucks and cars without multifunction turn stalks.

[tucsonjwt]

I will post a pic of the cruise control stalk for my 83 soon. (It has been very cold and raining for the past several weeks in the AZ desert and I have to work on my truck outside, so I have not been doing much on the truck lately. This is very unusual weather for my area, and I can no longer handle cold weather.)

Yes, 83 is apparently a one year only cruise control set up. If you look in the truck parts catalogs (LMC, Brothers, Classic Parts, etc.) you will find that there are cc parts through 82, then parts for 84 and up, but no 83 parts. I think my intermittent wiper module may also be a one year only part - I did find a NOS module but it was inoperable. The intermittent wiper control is on the dash - a small dial with an arrow on the switch.

The headlight dimmer is on the floor.

My cc setup has a push button on the end of the turn signal stalk to engage the cruise control, and the normal settings for resume, etc. I don't know why the 83 is different, but it may have to do with the wiper control on the turn signal stalk.

I am curious to see what happens when/if I get the VSS attached to the speedo head. As I mentioned above, the cruise will work when driving on a flat road with no a/c on, but will not work under other conditions. I have replaced the servo and the vacuum lines, but the circuit board in the red plastic box under the dash and the turn signal stalk are no longer available.

[hatzie]

That intermittent control you're describing is 78-83. Several outfits repop the controller. The controller uses common through hole discrete components so it's fairly easy to repair if its' not working... usually they need the electrolytic capacitors replaced. The switch isn't as easy to find but it's not impossible either.

I've had a minute to look at the 1983 GM CK Light Truck service manual.
Your Cruise III is a one year only stalk in the trucks. There's a line drawing of the turn/cruise stalk in the service manual. It looks just like the Dakota Digital HND-3 pictured above. I'd bet the HND-3 stalk will work on your rig.
Some of the CruiseMaster transducers had resume... they used the same switch. The 78-81 CK trucks with the 350 Oldsmobile Diesel had CruiseMaster with resume.

It is Cruise III tho. Not sure if it's an orphan early system like the 77 & 84 wiper delay modules or not. It sure looks like the same unit as the one on my 85.

1983 is Cruise III so the Cruise III textbook information will apply.
Download the 1983 Service manual and open PDF page 1462. Pg 1462 is the beginning of the 1983 Cruise Control service procedures.

[tucsonjwt]

I am attaching a pic of the cruise control/turn signal lever on my 83.

As I stated above, even without the VSS attached to the speedo head the cruise will work on a level road without the a/c on, and will disengage when the brake is depressed.

Regarding the cruise control circuit board in the red plastic box under the dash, several years ago I contacted Dorman (who makes aftermarket cruise control boards) and was told that they do not sell a board for my truck, but they offered to send it to their supplier and have them try to rebuild my board. That sounded iffy to me, so I declined their offer. Plus, I am sure that a one off custom board would not be cheap, especially without the OEM engineering available.

I did see a youtube video of a guy who replaced the capacitors on the small circuit board in the intermittent wiper module and he showed that the intermittent feature worked after he was done. I did not see any comments that the intermittent feature worked in the long term. I am not an electronic tech, so I would not attempt to rebuild it myself, and I would not spend $100+ to have someone do it. I would be more inclined to go back to a normal 2 speed wiper.

[tucsonjwt]

An interesting side note on my cruise - I have had a few different shops look at my malfunctioning cruise control over the years and they all have told me that it was working fine, even after I had explained the conditions under which it would not work.

[hatzie]

No reason it wouldn't work for several years after you recap it.
Replacing old dried out electrolytic caps is a time-honoured way to restore electronics back to operating condition. Since it's a through hole board it's bloody easy to do. Just don't use one of those 150 watt soldering guns and pipe solder