View Full Version : Who Has Installed Mark's Speedo Correction Box?

01-09-2008, 08:48 PM
I received it as a gift, bought from Slee. Athough the physical installation looks straightforward after readng the distructions, it is very confusing to figure out how to calibrate it using the many dip switches. I want to use my GPS which others have done. I searched Mud with no success. It looks easy to calibrate it using a percentage of change based on old vs new tire size, but I want it exact. I know the approx. size of the stock 275/70, but want to use the GPS.

Has anyone installed one? The first conversation with someone at Slee was not helpful. I guess I have to drive up there. I don't want to install it until I understand it. I want to be able to return it.

I have installed 2 Truespeeds on my Superduty trucks in the past and a knob was the only thing to turn instead of 8 or more switches in a row.

01-09-2008, 09:32 PM
I used the Yellowbox and from the install instructions, it looked similar. Take the glove box out and splice the box into the speedometer wire, than tie into another for power. Then set the switches to match the ratio of the difference you need.

01-09-2008, 09:50 PM
Ken, this is a plug and play Unit for the 80. The "plug" is the easy part.

01-09-2008, 10:12 PM
Ok, this is different than the truespeed Christo use to sell that hooked up like the Yellow box


Seems fairly simple for the switches, you use the table. Scroll down to page 6 of the document and use th pattern for either the 33" or 35" tire depending on what you have to give you the right ratio. Are the switches not labled to match the heading?

What is the issue?

01-09-2008, 11:47 PM
I think I figured it out. For example, If I am Showing 70mph on the speedo and the gps indicates 66, then I divide the two, equalling 1.06. Then I look up the closest number in the table and it will indicate which switches to turn on an off.

01-11-2008, 02:11 PM
An update: This is an extremely easy to install and calibrate speedo correction unit. In fact, you don't even need to drill a hole (in the body) to route the wires to the speed sensor plug near the T-case. The hole is already there in the form of a factory rubber plug that you can drill or cut out. The plug is on the top of the tranny tunnel and you have just a few flaps of carpet to pull back. The unit will mount to the side and to the front on the center console. It will not get kicked by any feet, it is high enough.

Mark's box thru Slee is 100% plug 'n play and takes no more than 30 minutes to install and calibrate with the GPS. It may take less time if you are not running back inside to get :beer:.

01-11-2008, 04:04 PM
Thanks for the update. I'm going to have to add this to my list.