Is the trailer hitch on G1 R1S "grounded"?

[Rivian Owner]

If you suspect the LEDs aren't conducting enough current to trigger the detection comparator in the Rivian you can get a 20 or 50 watt 20 ohm resistor and put it across the hot to neutral (ground aka return) wire. The resistor will increase the current flow enought to be detectable. You may be able to use a higher resistance (more ohms) and lower wattage resistor, but I don't know the Rivian's current detection threshold so some testing would be required. Also keep in mind that if you don't use a resistor with a sufficient wattage, the resistor will get hot and could burn you or your trailer, which is why I suggested a large wattage rating. If you find the resistor works you can wire it into the wire harness (proper attachment and insulation required) or look for one of the commercially available resistor kits made for this issue..

As for why the lights work when the trailer is on the hitch, as you suspect, the hitch is adding a return path for the current, so most likely you have a fault in the return path; either replace connections until things work, or use the ohm meter function on your multimeter to verify low resistance at each connection.

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[srjordan7251]

The trailer lights now work – sort of.

I confirmed the lack of continuity between the trailer’s tail light ground and the trailer plug ground pin. So without a working ground, the lights won’t work.

My conclusion (consistent with Zoidz’s advice) is that the trailer’s ground wire is no longer making an electrical connection where it is screwed to the bottom of the frame of the trailer. (The ground wire there is exposed and a little loose, connected via a rivet. At that location the frame has 20+ years of rust and corrosion. The lights were all using the frame as the ground, so they will not work if the frame doesn’t have a good electrical connection to the plug’s ground wire.)

Zoidz and “Rivian Owner” also noted that the hitch can sometimes prove an addition ground path to the towing vehicle, but I’m using a new hitch for the Rivian, and I’m guessing the nice thick black paint on the hitch is eliminating any electrical path through the hitch.

Side note: I did not try to determine if indeed the Rivian’s hitch is grounded to the vehicle’s frame. It strikes me that maybe it isn’t since unlike on an ICE vehicle, maybe you don’t want an electrical path through the Rivian frame onto a trailer, giving the EV’s HV battery.

As a temporary solution for the trailer, I added a wire from the light’s ground to the ground wire in the junction box (after confirming continuity on the ground wire between the junction box and the trailer plug). So I now have a path from the light’s ground to the plug’s ground wire. That direct ground path is working for both tail lights and all the marker lights, which are all grounded to the walls of the trailer.

My wife is now happy we can go pick up a new 11 year old Boer goat, who will be a companion for our recently orphaned and very lonely 12 year old Nutmeg. Once the old goats are happy, I’ll have a professional reconnect the plug’s ground wire to the frame (and also replace some of the unbelievably questionable wire connections I discovered).

Thanks for all the advice.

 

[Dark-Fx]

As a temporary solution for the trailer, I added a wire from the light’s ground to the ground wire in the junction box (after confirming continuity on the ground wire between the junction box and the trailer plug). So I now have a path from the light’s ground to the plug’s ground wire. That direct ground path is working for both tail lights and all the marker lights, which are all grounded to the walls of the trailer.

It's pretty trivial to just slap a new self-tapping screw into the trailer frame IMO. Just make sure you're staying away from any edges or welding.

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