Is a Relay Required for Normally Closed Installation of Brake Light Relay on a 2015 Jeep Cherokee

Question:

on 2015 jeep Cherokee latitude that has push button start do I need P/N Rm 790 on install of the brake light realy in normal closed wiring ? Thank You

asked by: Michael S

Expert Reply:

To determine if you need to use diode # RM-790 on the normally closed installation of the brake light relay # RM-88400 perform this test:

Start the engine and turn on the headlights. With a volt meter, such as # PT89ZR is you need one, test the tail light wire for 12 VDC+ current at any point between the splice made into the tow bar wiring you are using and the brown wire in the relay kit and the tail lights.

If the volt meter does not register voltage, a diode is not needed.

If the volt meter registers 12 VDC+, a diode is required.

So basically, the normally closed installation is as follows:

1.Remove the green wire from the kit. If you are using a Roadmaster Even Brake supplemental braking system, set this wire aside to use later.
2.Locate the brake-light-switch wire in your towed car.
3.Remove the brake light fuse.
4.Cut the brake light wire a few inches away from the "cold" side of the brake light switch.
5.Attach the relay to the wiring for the RV braking monitor. The diagram above shows where the blue wire attaches the relay to either a Roadmaster Even Brake or BrakeMaster system. The green wire may be needed here.
6.Connect the black wire of the relay to the brake light wire near the brake light itself using the included blue butt connector.
7.Use a voltmeter to identify the wire in your aftermarket light harness that is conducting the tail light signal. Typically, this is a brown wire.
8.Using a 16 - 14 gauge butt connector (sold separately), attach a section of 14-gauge wire (sold separately) to the end of the red wire. Trim the new 14-gauge wire and connect it to your aftermarket wiring harness.
9.Start your engine and turn on your headlights. Test the tail light wire with a voltmeter. If your voltmeter doesn't register any voltage, move on to step 10. If 12V DC registers, you will need to install a single diode (RM-790; sold separately).
10.Ground the white wire to your towed car's frame.
11.Secure the relay with the included wire ties.