Speedometer correction!

[7783911]

also, which one is best for 77 targa with 915 transmission..sounds like the 2 wire splice is?

Yellow Box v5 - with Splice Wiring Harness
Yellow Box v5 - with Custom Plug-n-play wiring harness*
Yellow Box v5 "2-wire" - with Splice Wiring Harness (vehicles with inductive coil sensors only)

[spuggy]

The Yellow Box has a little brain in it. Needs power (5V or 12V), and ground. Intercepts the speedo signal, corrects according to the switch settings and outputs the corrected signal to the instrument. Very simple, very robust.

Everything you need in terms of connections is right there at the back of the instrument, no need to run any wiring anywhere. Dry, safe, concealed and protected nestling in the dash.

The Yellow Box has a detachable harness plug with 4 wires coming off it. Installation manual here https://yellr.com/yb4_insta.pdf

Couldn't be much simpler, if you can make crimped or soldered connections. Easily reversible, no need to cut factory wires.


Disconnect the speed sensor connection to the speedo, use as input to the Yellow Box (i.e. put a male spade on the Yellow Box harness wire and plug the harness female spade into it). Put a female spade on the Yellow Box speedo output, connect to the speedometer terminal you just plugged into the Yellow Box. That's the intercept part done.

12V power and ground are right there on the back of the speedo; I just put female spades on the Yellow Box wires and used a male 2:1 female piggyback on the speedo terminals to supply both the Yellow Box and the original connection for both power and ground.

Mark the tire (driven wheel). Measure one full revolution on the floor. Figure out the standard tire size for your speedo part #, calculate rolling diameter of that. Figure out the %-age adjustment between what you have versus what the instrument was designed for. Look the number up in the table, set the DIP switches. Pretty sure my adjustment factor ended up being nearly 15%.

Drive the car. Check speed against a GPS or laser speed-trap, fine-tune until happy (e.g. adjust for any calibration error on your specific instrument, or calculation error earlier).

I was happy as soon as I could drive the indicated speed limit and not get passed by every other car on the road - or drive with traffic and not have the speedo telling me obvious lies... The instruments themselves seem to be pretty accurate, up until it's a moot point/you're not really looking anymore... They just had to make them read fast for legal reasons (like everyone else).

[7783911]

Thank you...sorry but a couple of more questions

which yellow box is the correct one to order? other then that which is the correct sensor wire to use since this picture shows two wires in

[horolicious]

I just had my speedometer calibrated by police. I was going 81mph in 50mph zone. The speeding ticket states I was going 81, although I did not disclose the number to the office.

4

[7783911]

sorry, based on that picture..

take power from 2:30 o clock with piggy back connector
take ground from brown (2 of them) at 5 oclock
but this picture indicates two sensors..i assume #1 (B/R) is the target wire?

[911 Rod]

What do these things cost?

[7783911]

I am seeing about 100$

Official home page of the Yellow Box Speedo Recalibrator

[spuggy]

Originally Posted by 7783911

which yellow box is the correct one to order?

I'd order

Yellow Box v5 "2-wire" - with Splice Wiring Harness (vehicles with inductive coil sensors only)

"reed switch" == "inductive coil sensor". No idea what the difference is between v4 and v5 - there's only v3/v4 instructions, so probably just build differences. I've got the v4.

Originally Posted by 7783911

which is the correct sensor wire to use

The sensor is a reed switch closed (making the circuit) when the magnet is over it, and open otherwise.

According to this



one connection at the speedometer is instrument ground, the other is terminal 31b. Pretty sure I connected the Yellow Box to that.


From https://yellr.com/yb_home.htm

[7783911]

Thanks ALL

I ve ordered and looking forward to posting success