Brake Controller Ground and Sharing Power Wire for an ETBC7 Hardwire Installation

Updated 10/02/2017 | Published 09/30/2017

Question:

Looking at installation instructions for ETBC7, Im wondering why the ground wire for the brake controller has to be connected to the battery negative, versus just chassis ground same as done for ground in the 4 way and 7 way connectors. Connecting the controller ground to battery requires running one extra wire through the firewall, versus just using a chassis ground point which are typically plenty under the steering wheel. Also, if installing the 4 way and 7 way wiring at the same time, can I use ONE 10AWG wire running from the battery + terminal, vs 12AWG for the 4 way and 10AWG for 7 way? Since the 4 way and 7 way are never used at the same time, this seems fine. As far as fuses go 10A for 4 way and 40A for 7 way, I can put them in the trunk in parallel after splitting the 10AWG, or I can put them sequentially - 40A under the hood, and then 10A in the trunk for the 4 way. Again, electrically this sounds fine as the 4/7 way are never used at the same time, and the 4 way controller uses very little current. There is some inconvenience with having fuses in different places.

asked by: Alex

Expert Reply:

Brake controllers require a fairly substantial ground which can be achieved by connecting the controller ground to the negative battery terminal. In some situations a chassis ground is fine but if you are running wires through the firewall anyway might as well go for the best ground location available.

If you are installing a powered 4-Way wiring harness first it is permissible to have one 12 volt power wire for both it and the 12 volt wire on the ETBC7's 7-Way adapter. A 4-way by itself does not use 12 volt power. On powered versions of 4-Ways the 12 volt power is what is powering the trailer lights (instead of the trailer lights pulling power through the vehicle tail light wiring). So in this case they would be used at the same time assuming you choose to use 1 power wire for both functions.

You would want to have the power wire split somewhere with the 40 amp circuit breaker on the line to the ETBC7 power wire and the 10 amp fuse for the 4-Way's power wire. Where you place them is up to you. You just want to make sure that the 4-Way is fused separately.

expert reply by: Michael H