UPDATE: I'm no longer using the Holley EFI 553-103 5.7" Touchscreen LCD unit, but I'll leave this page posted for informational purposes.
I'm currently using the Holley EFI 553-106 7" Digital Dash Touchscreen, and the Holley EFI 553-108 3.5" LCD Touchscreen simultaneously.
The dual 4-pin Molex Mizu-P25 connector, easily allows multiple Holley EFI devices to be connected onto the CAN1 Bus/power circuit.
One Holley EFI device connects to Switched +12V, Ground & CAN Bus (LINK), and the next device simply plugs into its dual connector.
https://forums.holley.com/showthread...2052#post92052 (My Digital Dash & 3.5" TSLCD Tripod/PanaVise Swivel Pedestal Mounting)

Currently, the Digital Dash has more utilities & tuning capability than the 3.5" LCD Touchscreen; it can switch Global Files, but it also has
virtual switches (LINK). The 3.5" LCD Touchscreen can quickly switch Global Files (stored on SD Card), update ECU firmware, temporarily
disable Idle Spark control (check timing synchronization), perform TPS Autoset calibrations, change Rev Limiters Main/#1/#2, change
Timing Retards #1/#2/#3, idle speed RPM & IAC Ramp Down parameters, Electric Fans #1/#2, disable Closed Loop and/or Learn, disable
Advanced ICF Tables, 10 Input & 10 Output I/O Monitors, Multi-Gauge screens, and basic tuning changes in all ICFs. Both units datalog.
This is how I mounted my Holley EFI 5.7" Touchscreen LCD. The beauty of the PanaVise "mobile electronics mounting" pedestal, is I can swivel
the TSLCD 360° (limited to the slack in the wire harness). I can swivel it up, down, toward the driver or passenger. I custom made the horizontal
strut for vibration support. The other cool thing is, the PanaVise top mounting pad has the same bolt pattern as the Holley 5.7" TSLCD center
four threaded holes. That's nice for a quick & easy installation. Shorter pedestals and windshield suction mounts are available too. I'm glad the
5-wire harness is very long, because I didn't have to lengthen it to reach the EFI harness.
UPDATE: It's now a custom tripod I made using the same PanaVise swivel pedestal (LINK).

5 wires:
1 battery +
1 battery
1 switched 12V
2 CAN Bus

The CAN Bus wiring should look exactly like figure 3, on page 3 of the 5.7" Touchscreen LCD manual:
http://documents.holley.com/199r10524rev4.pdf (5.7" TSLCD Manual)
You must have ECU firmware version 330 or higher for the touchscreen to function properly.
https://www.holley.com/document/tech...0.2_update.zip (Holley V2 5.7" TSLCD Updates)
https://www.holley.com/products/fuel.../parts/553-103 (5.7" Touchscreen LCD)

PanaVise web pages:

Click image for larger version. 

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Holley 553-103 5.7" LCD Touchscreen external dimensions:
5 1/16" height
6 1/2" width
1 3/8" depth

Holley 553-108 3.5" LCD Touchscreen external dimensions (for comparison):
2 7/8" height (2 15/16" mounting sleeve height)
3 3/8" width (3 5/8" mounting sleeve width)
3/4" depth (1" mounting sleeve depth)

Holley 553-106 7" Digital Dash Touchscreen external dimensions (for comparison):
4 5/8" height
7 1/2" width
1" depth

Holley 553-112 6.86" Pro Dash Touchscreen external dimensions (for comparison):
3 7/16" height
7 9/16" width
1 1/4" depth

Holley 553-111 12.3" Pro Dash Touchscreen external dimensions (for comparison):
5.81" height
13.44" width
1.25" depth

• Touchscreen "Switch Panel" setup instructions for user created I/O:
Create an Input in the software's Inputs/Outputs ICF. (Example: "LCD Switch Input")
Assign this Input in the Pin Map's "View LCD" screen.
Create a corresponding Output in the software's I/O ICF. (Example: "LCD Switch Output")
Configure the Output by using the created Switched Input Trigger and select Enable.
Assign this Output in the Pin Map's "View Outputs" screen.

Touchscreen "Switch Panel" setup instructions for preexisting software I/O:
Enable the predefined Input in the EFI software.
Assign this Input in the Pin Map's "View LCD" screen.
Assign the corresponding Output in the Pin Map's "View Outputs" screen.
Configure the predefined Input & Output Type in the software's Inputs/Outputs screen.

http://forums.holley.com/showthread....7745#post57745 (Virtual Switches Setup)
http://forums.holley.com/showthread....8389#post58389 (How To Create A Custom Input/Output)

• The 3.5" & 5.7" LCD Touchscreens can also quickly & easily change Global Files by storing them on the SD Card. And
now the Digital Dash is also capable of storing/changing Global Files, except it's stored on a USB flash drive. I have the
Digital Dash & 3.5" Touchscreen units, but I store my "known to be good" & "emergency" Global Files (LINK) on the 3.5"
TSLCD, because it conveniently holds the SD Card inside. I actually prefer it over the 558-407 Multi-Map Selector Switch.