davebhm Posted July 21, 2023 Share Posted July 21, 2023 I've got zero experience with van modifications but I am about to purchase a Transit Connect (2019), I'm having a leisure battery and split relay installed in the rear of the van. I've been told the CAN Bus network can be complex but I would like to run an additional switch to power the wipers and the fans/heaters from the leisure battery whilst the ignition is turned off. To clarify I want to be able to turn the wipers/blowers on and off from a switch in the rear of the vehicle and I want this to be powered from the leisure battery whilst the vehicle ignition is completely off. Does anybody have any experience running separate or additional switches to power equipment from alternate power sources? Would be keen to know if anybody has any advice, knowledge of problems I need to be aware of or equipment I should look out for? Quote Link to comment Share on other sites More sharing options...
Don Ridley Posted July 22, 2023 Share Posted July 22, 2023 The wiper circuit is complicated. The switch sends a LIN network signal to the body control module (BCM). The BCM sends a LIN signal to the wiper motor. The BCM is looking at a lot of information to determine how to control the wipers like the rain sensor, requested speed etc.. You will not be able to control the wipers unless the BCM is running. You will have similar problems with the fans and heater since the BCM controls them also. You best bet is to add battery capacity that will power the entire vehicle. There may be problems with the battery nonitoring system (BMS) if your model year has one. The BMS monitors the battery state of charge and turns off components if the charge is too low. It won't know you have multiple batteries and may not function properly. Quote Link to comment Share on other sites More sharing options...
Bert Remington Posted July 22, 2023 Share Posted July 22, 2023 (edited) Quote The wiper circuit is complicated. Yes it is. The LIN https://en.wikipedia.org/wiki/Local_Interconnect_Network is non-CANbus and it may be difficult tracking down the message descriptions and finding interface devices. Probably better to control the BCM, etc via the HS and/or MS CANbus. I discovered two devices to accomplish this: Ford's Generic Function Module (Upfitter) and Intermotive's UIM, both of which require external software to program. Your first step will be purchase of a Wiring Diagrams manual, 1 1/2" of thin paper. Daunting... What Climate Control are you getting? Edited July 22, 2023 by Bert Remington corrected typo Quote Link to comment Share on other sites More sharing options...
Bert Remington Posted July 22, 2023 Share Posted July 22, 2023 Here's a bit more explanation of the LIN/windshield wiper motors relationship (at least from my 2020 Wiring Diagrams). The motors basically have three wires: Ground, Power, and LIN. When a "Wipe" command is transmitted via the LIN, the motor operates. I believe for simplicity and failsafe reasons, it only operates for one sweep else "Wipe Start" and "Wipe Stop" commands would be required. The rear wiper motors take the more traditional three wires: Ground, Power, and Start Wipe. They seem to be controlled by the BCM but it isn't clear. The Climate Control circuit is more complicated. Quote Link to comment Share on other sites More sharing options...
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