Speedometer/Odometer issue, thought it was anold yellow box calibrator but it's actually Superlift Truspeed.

[Gman094]

Recently bought my buddy's 96 80 series that has 4.88 gears and 35's. He's had intermittent issues with the speedometer the last two years where he'd be driving at like 30mph and the dash is reading 120mph. Bought the car on Saturday and have driven maybe 120-150miles since then but because the speedometer isn't functioning right, it's causing the odometer to roll over at like 5x what it should be. My friend said he had a yellow box installed behind the glove box about 16 years ago and I'm thinking the yellow box may be fried at this point. I ordered the lutzauto calibrator(before I knew he had the yellow box) because it seems like an easy install. Trying to decide what the best course of action is, whether to leave the yellow box in there and install the lutzauto when it arrives or remove it completely and install the lutzauto piece. The yellow box is 16 years old at this point so it wouldn't surprise me if it just died. Any thoughts/recommendations would be much appreciated.

-Will

 

[80t0ylc]

Recently bought my buddy's 96 80 series that has 4.88 gears and 35's. He's had intermittent issues with the speedometer the last two years where he'd be driving at like 30mph and the dash is reading 120mph. Bought the car on Saturday and have driven maybe 120-150miles since then but because the speedometer isn't functioning right, it's causing the odometer to roll over at like 5x what it should be. My friend said he had a yellow box installed behind the glove box about 16 years ago and I'm thinking the yellow box may be fried at this point. I ordered the lutzauto calibrator(before I knew he had the yellow box) because it seems like an easy install. Trying to decide what the best course of action is, whether to leave the yellow box in there and install the lutzauto when it arrives or remove it completely and install the lutzauto piece. The yellow box is 16 years old at this point so it wouldn't surprise me if it just died. Any thoughts/recommendations would be much appreciated.

-Will

Yeah, you need to find the Yellowbox control unit. It's adjustable, but it's possible to be malfunctioning if there is that big of miscalculation. Definitely disco the adapter harness at the transfer case. and reconnect the OEM harness. to see if the Yellowbox is the culprit. Your ECU uses a speedometer input, so the erroneous mph will affect your 80's performance in fuel mileage and engine smoothness.

Edit: Corrected speedometer connection to drive train.

 

[Gman094]

This may be a silly question but I thought the yellow box was installed behind the glove box and not under the car by the transmission. I have to look around tomorrow to see if I see it. Assuming it’s the yellow box, I imagine the OEM harness will work but still be off but by a smaller amount, is that a fair assessment. I need to look at the wiring guide for the yellow box tomorrow and familiarize myself with where it’s located.

 

[80t0ylc]

This may be a silly question but I thought the yellow box was installed behind the glove box and not under the car by the transmission. I have to look around tomorrow to see if I see it. Assuming it’s the yellow box, I imagine the OEM harness will work but still be off but by a smaller amount, is that a fair assessment. I need to look at the wiring guide for the yellow box tomorrow and familiarize myself with where it’s located.

For my Yellowbox, (approx 8 yrs old) there is a control unit mounted ideally somewhere in the cab. A harness (3 or 4 conductor cable) goes from the control unit though the floor to the transfer case where the OEM speedometer connector is. My '94 is on the driver's side (IIRC). The Yellowbox harness end has an adapter that you install between the OEM speedometer connector and the transfer case connector. You can just pull the Yellowbox adapter out and replug the OEM speedometer cable back into the transfer case and see if you get a more reasonable reading on your speedometer.

My Yellowbox is currently disco'd because it got damaged and I just haven't repaired it. I live with the incorrect MPH, because my GPS gives me the correct speed. I'm running 35's with 5-29 gears, so the Yellowbox was nice, but not totally necessary. Although for best performance, you do want to have accurate mph fed to the ECU.

Edit: The speedometer connector is on the transfer case which is directly behind the transmission. I just seem to remember it being on the driver's side near the rear of the case.
2nd Edit: Corrected location in previous edit and text of post.

 

[80t0ylc]

Confirmation - The speedometer connector on my '94 is on the transfer case near the rear output shaft, driver's side. If you ignore the dirt and minor fluid leaks in the following pics, it might be helpful if your '96 is in the same place. Also, the skid plate is custom fabbed by @CreeperSleeper and will be different than the OEM skid plate.

Edit: went back to previous posts and corrected the location reference.

 

[efjayatee]

I went the lazy way. Im on 4.88 w/37s and I use a digital GPS speedometer pod off Amazon $37 cigarette plug. Calibrated to goggle map mph.

 

[Gman094]

Confirmation - The speedometer connector on my '94 is on the transfer case near the rear output shaft, driver's side. If you ignore the dirt and minor fluid leaks in the following pics, it might be helpful if your '96 is in the same place. Also, the skid plate is custom fabbed by @CreeperSleeper and will be different than the OEM skid plate.
View attachment 4180458
View attachment 4180459
Edit: went back to previous posts and corrected the location reference.

Would you mind taking a photo of the OEM harness that the yellow box is plugged into. Mine looks identical to the photo you posted but just want to make sure I’m plugging in and unplugging the right stuff.

 

[80t0ylc]

Would you mind taking a photo of the OEM harness that the yellow box is plugged into. Mine looks identical to the photo you posted but just want to make sure I’m plugging in and unplugging the right stuff.

OK, stick with me on this. As I said, my Yellowbox is disco'd currently. So I'll try and explain the pics and pdf file included. The pdf (2 pages, BTW) is the instructions that were included when the Yellowbox was purchased for your convenience, in case you don't have access.

This pic shows the tag that was on the bag that the Yellowbox came in plus the connector that was ripped of the harness when it got snagged and broke.

This pic is the end of the harness from the control unit that plugs into the transfer case. Imagine (if you will) the connector shown in previous pic, on the end of the loose wires in this pic. So what you have on the end of a healthy harness, is 2 connectors. To install the Yellowbox, you 1st remove the existing OEM speedometer cable connector from the transfer case and install it into a connector on the Yellowbox harness. And the other connector on the Yellowbox harness will go into the connector on the transfer case that the OEM speedometer cable was originally in. This makes for an awkward harness bundle that needs to be tied up, out of harm's way (ask me how I know...lol).

 

[80t0ylc]

BTW, if this harness bundle that's near the transfer case connector has been damaged in any way, it may be the problem with your Yellowbox.
Edit: one last thing, it seems that even the wind can pull at this harness. So even if you don’t off-road, tie it up securely. I thought I had it tied up securely, but found out the hard way that the wind just going down the road 70 mph will give trauma to the harness.

 

[Gman094]

This photo above is a little misleading because the wires from the side plug are separate from the plug that you see in the top on the back.

side view similar to the front.

This is where I'm a little confused, the red/black/white wires don't connect to the big white plug you see. The red/black/white wires go behind it and end somewhere that's harder to get a picture of. Part of me is wondering if the wiring was spliced in order to put the yellow box on given how old it is. I wasn't sure if the harnesses were released when this vintage of yellow box was released.

 

[80t0ylc]

Yeah, sorry I couldn't help, but it would be nice to get a schematic and version of Yellowbox that you have. Mine is version 5 and is advertised as plug and play, meaning no mods to OEM wiring were necessary (other than the connector shuffle - which is no big deal). If you're sure it's a Yellowbox, you might reach out to them at yellr.com on the email link to get some help. They're in Australia and IIRC it took several weeks to get the unit when I ordered it almost 10 yrs ago. But they replied back to me next day when emailed.

 

[landtank]

Back in the day I wrote a procedure for installing a yeller box behind the glove box. The idea was to keep it out of the elements.

It was openly available on the site so it’s possible it was used for the install.

Erratic speedo is a bad connection. I’ve seen it a few times and I’m sure the box is fine.

 

[80t0ylc]

@Gman094 You might want to check out this thread (Lutz Auto) if the Yellowbox doesn't pan out. Looks similar hardware and price, plus easier to calibrate than Yellowbox. I just ordered a pin kit to fix my Yellowbox setup since the wires got pulled out of the connectors. I've been meaning to fix this since it happened a couple yrs ago and this thread motivated me to "get r done". Thanks and good luck on your setup!

 

[Gman094]

@Gman094 You might want to check out this thread (Lutz Auto) if the Yellowbox doesn't pan out. Looks similar hardware and price, plus easier to calibrate than Yellowbox. I just ordered a pin kit to fix my Yellowbox setup since the wires got pulled out of the connectors. I've been meaning to fix this since it happened a couple yrs ago and this thread motivated me to "get r done". Thanks and good luck on your setup!

It’s funny you mentioned that because I had ordered the lutzauto piece Monday as I was trying to figure out the yellow box issue. I think the challenge I’m having is that it feels like whoever installed the yellow box to begin with may have spliced wires rather than use a harness. If that’s the case then it makes things a little complicated and im not entirely sure how to fix it yet.

 

[Gman094]

Back in the day I wrote a procedure for installing a yeller box behind the glove box. The idea was to keep it out of the elements.

It was openly available on the site so it’s possible it was used for the install.

Erratic speedo is a bad connection. I’ve seen it a few times and I’m sure the box is fine.

@landtank Do you remember how long ago you wrote the procedure? Just trying to narrow down how far back to look. This is a picture of behind the glove box and I didn’t see a yellow box but I’ll look again.

 

[landtank]

The yeller box would be up on top of the AC box that you can see in the picture

 

[Gman094]

The yeller box would be up on top of the AC box that you can see in the picture

@landtank thanks, I looked and the plot thickens. Trying to figure out the best way to remove this thing and just go with the lutzauto option.

 

[landtank]

That was the Cadillac of speed calibration back in the day. You could calibrate for 2 different sized tires and with a flick of that switch change the Speedo to match the tire you were running

I still don’t thing it’s in that box.

 

[landtank]

that happens to be my first 80 bought in 2000 from dentist.