This tech page addresses setting up a Defi-Link system toallow control of 2 EGT gauges while only interacting with one visiblecontrol unit.

NOTE: This tech page does NOT address installing the gauges inthe car. There will be a separate page to address this in the future.

The modular Defi Link system starts with the control unit. All theelectronic sensors are connected to the control unit, and the gaugesare then hooked up to the control unit in a daisy-chain. Replay (3minutes), peak hold, warning are all activated through the controlunit. The new Control Unit II also features a differential fuelpressure mode, which displays fuel pressure relative to manifoldpressure (for 1:1 rate fuel pressure regulators). (0.)

The problem with the out of the box Defi-Link setup for V enginecars is that only one EGT gauge is supported per control unit. The onlymechanism for using 2 EGT gauges is to buy a second control unit forthe one gauge, which then has synchronization problems, i.e. you wouldhave to press Peak on each control unit to see the peak values for allgauges.

This tech page will address linking two control units together suchthat a button press on the first unit causes the same button press onthe second, which will allow synchronized operation of the second EGTgauge and allows only one unit to be visible.

Tools

• 1. Multi-meter with continuity and DC voltage capabilities
• 2. Solder (resin core)
• 3. Soldering iron (not a soldering gun)
• 4. Wire strippers
• 5. (optional) 75ohm crimpers. I used them as 'pincers' tohook/unhook the Defi-Link wiring harnesses as the clips are very small.
• 6. Philips head screwdriver
• 7. High speed rotary tool with grinding bit
• 8. (optional) cutting disk for rotary tool
• 9. (optional) SuperGlue
• 10. (optional) drill and very small drill bit
• 11. (optional) needle file

Parts:

• 2 Defi-Link EGT gauges (and optional other gauges)
• 2 Defi-Link Control Unit II boxes
• 2 RJ-45 female connectors (purchased mine from Radio Shack, $4.50 each)
• 1 appropriate length of Cat 5 cable with male connector ends (from Radio Shack, 3 feet, $4.99)
• (optional) additional length of Cat 5 cable used to strip apart for wiring inside the Control Units
• (optional) small momentary switch to cut the 'Warning' signal to the other unit
• (optional) toothpick (for extending the momentary switch button)

Procedure:

NOTE: The procedure for wiring each unit is identical. In mycase, I wired one unit with the external connector on the left and thesecond unit with it on the right. Therefore in some of the referenceimages you may see the wires going the opposite direction. Theprocedure is the same.

1. Lay out your work area. For full testing, you will need thecontrol units, a battery, the provided harnesses and gauges. In theexample shown on this page, you will see a Boost Gauge, a Fuel Pressuregauge, and two EGT gauges. (2.) shows area after everything is complete.

2. First verify that everything works. On the first control unit,plug in the sensors for one EGT gauge and any other additional gauges.This is needed so that the gauges will not go into an error mode whenpower is applied. The plug locations are noted on the top of theControl Unit case. Plug the gauge harness into the unit and run it tothe first gauge. For each additional gauge, run the provided harnessfrom the prior gauge to the additional gauge.

3. Plug the second EGT sensor into the second Control Unit. Plug thegauge wiring harness into that control unit and connect it to thesecond EGT gauge.

4. Plug both power harnesses provided into each Control Unit.Take the power wires (red, white, and orange) from each harness andtape them to the positive terminal on the battery. Take the groundwires (black) from each harness and touch/tape them to the negativeterminal on the battery whenever you want to apply power. If all workscorrectly, you will see the gauges go through their opening sequence.

5. Once correct function is verified, remove power and remove thecover on one of the units. There are 5 visible philips head screws tounscrew and then the unit will come apart into 4 pieces, the top cover,bottom cover, button panel, and breadboard. (3.)

6. You will see 6 buttons with red pushbutton fronts on thebreadboard. On the other side of the board you can see 4 solder pointsfor each button. With the buttons facing you, the front left solderpoint is the signal post that we will tap into. (4.) shows signal posts indicated with red circle.

7. This step assumes you are using some Cat5 cable as the source forthe signal wires. If you use some other wire, apply the sameprinciples. The benefit of using Cat5 wire pairs is that each wire iscolor coded making it easy to match up to the other side and to theRJ45 connector. Take a length of cat5 cable and split the insulationoff of it to expose 4 2 wire pairs. Untwist the pairs and choose 6wires to use (one for each button). The color choices are irrelevant,but make sure that you match the button/color combinations on bothunits. In my case I used the brown, orange, green, blue, green/white,and blue/white wires. You can clip off the other two wires as they willnot be used. (5.)

8. Decide which side of the unit you want the connector on and laythe wire out accordingly. Make sure that the wires are long enough forthe last wire to reach the furthest button post. Start with the closestbutton and solder the desired color wire to the post. (6. shows the farthest three posts soldered.)

NOTE: The rest of this tech page shows the RJ-45 connectorattached near the front of each unit. After attempting to mount thevisible control unit in the center console area, I discovered there wasno clearance and had to move the RJ-45 connector to the rear of theunit. Decide where you ultimately want the visible unit mounted and usethat information to make a decision about where to place the RJ-45connector on the unit.

9. Continue with the next closest post, etc. until you have done all6. Pull the wires tight (remove slack) and decide where you want theRJ-45 connector to extend out of the unit (front/back/middle/etc). (7.) shows completed unit

10. To allow the wires to run properly without interfering with thecase, you need to dremel a small amount out of the breadboard to allowthe wires to seat inside it. This shows a chunk out of the left side ofthe breadboard. If you wired the opposite way, simply dremel out thatside. There should be plenty of room but be careful not to dremel outinto any of the traces on the breadboard. As well, on the left side, becareful not to dremel into the holes that are already drilled in thebreadboard. (8.)

11. To expose the wires outside of the unit, dremel out a smallhalf-moon hole in the upper cover for the wiring to run through. Ifound that a round sanding bit on the rotary tool (see image 1.) worked very nicely for this. (9.)

12. Take the six wire ends and position them in an RJ45 femaleconnector. The one that I bought from Radio shack had color codesaround the outside that I used to match up the wires. This guaranteedthat I would get proper connection between the two connectors. It alsocame with a small plastic tool to punch the wires into the connector. (10.)

13. At this point, it's probably wise to make sure you haveconnectivity. Use a multimeter in continuity mode, and touch one probeto each soldered connection while touching the other to the leadsinside the female RJ45 connector. You should hear a tone for each onewhen you hit the right combo. If not, verify all of your solderconnections until you do get tone for each one.

14. Put the button panel back into the base cover. Drop thebreadboard in. There is a guiding pin on the front left side that thebreadboard has a hole for to line things up. Make sure the wires youhave attached are feeding through the dremeled out gap on thebreadboard and then put the top cover on. If everything is donecorrectly, the wires should feed through the hole you drilled in thecover. I left a small run of insulation around the wires, allowing theexposed wiring to be somewhat stiff. The unit is now complete (11.)

OPTIONAL STEPS

As it stands now, there is only one problem with the hack, which hasto do with setting the warning mode. Warning mode works in a roundrobin fashion. This means that each time you press the warning button,the unit will cycle to the next gauge that is attached to it. Forinstance, in my case where boost, fuel pressure, and one EGT areconnected the unit will move from EGT -> fuel pressure -> boost-> back to EGT as I press the button. Once the desired gauge isselected you use the up/down keys to change the warning value for thatgauge.

The reason that this behavior is undesirable with the hack isbecause only one gauge is connected to the hacked unit. Since pressingwarning on the main unit triggers the same keypress on the second unit,that second EGT will ALWAYS be in warning set mode when you press thewarning button, such that if you cycle to boost on the main unit andstart changing it's value with the up/down arrows you willsimultaneously be changing the setting on EGT 2.

Without following the optional steps, what you will need to do isset all of your gauges on the main unit (while EGT 2 changeswilly-nilly) and then finally cycle to EGT 1 on the main unit (EGT 2will still be in warning mode), zero them both out to get EGT 2 matchedup and then set them to the proper level. This is perfectly doable, butI thought it would be painful over time, if you need to frequentlychange warning levels on the other gauges, so I came up with a solution

To solve the problem, we simply need to interrupt the signal goingto the warning button on the second unit such that it is triggered onlywhen we want it to be. This is done by wiring the Warning button signallead from the main control unit through a momentary micro-switch andthen on to the RJ-45 connector. This will then only allow the signal totrigger warning mode for the second unit when the microswitch ispressed in conjunction with the warning button on the main controlunit.

If you do not want to wire a momentary switch, simply followsteps 6-14 for the second unit and then proceed to the TESTING section.If you do choose to install a switch, follow all steps 6-13 for thisunit EXCEPT for the Warning button lead.

15. I snagged a small three-way momentary switch from Frye's for $1.49. (12.)This switch takes voltage from one side and passes it through one leadwhen not pressed and through the other when it is pressed. This willrequire extending the button so I broke the top of the switch off toget at the small button inside it.(13.) If you buy a switch,make sure that it is relatively small form factor, especially inheight. In this case, the switch assembly will be placed on the bottomof the case underneath the breadboard and behind the other buttons sothere is enough clearance. Verify clearance of your switch before proceeding!

16. Remove the button from the switch and dremel it in half. Theback half will go back into the switch and the front half will be onthe Control Unit faceplate (14.) 1=original button. 1.1=back half and 1.2=front half after dremeling.

17. Take a toothpick or some other small rod that can be used as abutton extension. Cut the toothpick to have a flat end and supergluethat end to the back of the visible part of the button.

18. Next choose a place for the button to appear on the faceplate. Ichose beneath the 'Warning' button so I could roll my finger on both ifneeded to activate the warning mode on control unit two, giving mesingle finger operation. I used a small modeling hand drill to drill ahole in the approximate position that the button would be placed. BeVERY careful in deciding placement here as the buttons on the faceplateare attached by a small run of plastic (see rear of plate). If youaccidentally drill through that you will ruin the faceplate. There arealso LED conduits that have to be considered, which limits youroptions. (15.) inset shows the hole after completion)

16. Remove the button from the switch and dremel it in half. Theback half will go back into the switch and the front half will be onthe Control Unit faceplate. (14. 1=original button. 1.1=back half and 1.2=front half after dremeling.)

17. Take a toothpick or some other small rod that can be used as abutton extension. Cut the toothpick to have a flat end and supergluethat end to the back of the visible part of the button.

19. Dremel out the plastic on the rear of the faceplate to giveclearance for the small button to fit. Be very careful not to dremelall the way through and stay well clear of the thin runners for thefaceplate buttons. (16. shows completed dremel work)

20. Take a needle file and use it to carefully enlarge the hole. (17.)

21. Continue with the file and create a hole sized for the button front to be able to come through and move easily. (17.) (inset) Work carefully and don't rush this part. If the hole gets too big you've just ruined the faceplate.

22. Take the button/toothpick combo and verify that it seats in the newly created hole properly. (18.)

23. Take the bottom case and determine required placement of theswitch based on where you drilled the front panel button hole. You willprobably have to dremel off some of the plastic supports to make roomfor the switch (yellow area in 19.). Make sure you do notremove the square support that separates the differential pressure LEDfrom the rest of the panel (red square in 19.)

24. Put the front button panel with the extended button/toothpickcombo installed into the bottom part of the case. Use this to determinewhere to mount the actual switch and superglue the switch into place.If done properly you can then trim the end of the toothpick to fitinside the switch assembly to press against the back half of the buttonthat we dremeled off before, causing the switch to trip. (20.) shows glued and working button assembly

25. Solder connection from Warning button to one pole of themomentary switch. I used a long length of one pair of the cat5 cable. Iwrapped the wire around the center pole to hold it steady to the switchand kept some excess coiled up in the case to allow the breadboard tobe removed in the future and set to the side since the momentary switchis glued directly to the case. (21.)

26. Solder connection from other pole of momentary switch and run itto the RJ45 female connector and punch in. I used the same tactic hereas I did in step 25. (21.)

27. Dremel the breadboard and case as explained in steps 10-11. Putthis unit back together with the momentary switch installed. (22. shows completed primary unit with exposed momentary switch button)

28. Plug Category 5 network cable into both RJ45 connectors to connect the two units together.

29. Power up the units as explained in Step 4.

30. Verify that pushing Peak on one unit causes all gauges to go into Peak mode.

31. Verify that pushing Record on one unit causes all gauges to go into Record mode.

32. Verify that pushing Play on one unit causes all gauges to go into Playback mode.

33. Verify that pushing Warning causes the first gauge on unit oneand the EGT gauge on unit two to go into Warning set mode. If momentaryswitch was installed, the EGT gauge on unit two should NOT go into warning set mode.

34. If momentary switch is installed, hold momentary switch whilepressing Warning should cause EGT on second unit to go into Warningmode.

35. On any gauge in warning set mode, verify that the up/down buttons move the warning level on the gauge.

36. Get the EGT on unit two into Warning mode (Step 33 or 34) andthen verify that pressing the up/down buttons on the primary controlunit cause the EGT warning levels to change.

(23.) Shows the final configuration of the three gagues inthe 300Degree pod (boost gauge is on the A pillar) with a singlecontrol unit visible where the stock clock was. The second control unitis hidden behind the gauges in the console cavity.

Originally published 02-27-2004