Troubleshooting Wiring on a 1990 Toyota Pickup While Installing Curt # C55379 Harness

Question:

I have a 1990 toyota pickup, and an old trailer with just the 2 lights in the back. I bought the C55379 converter and connected everything as per the instructions. I dont have turn signals or brake lights, Ive checked the grounds and they are on bare metal, I have .3 ohm between the trailer and the truck.the light sockets on the trailer have been cleaned and are in good condition, Ive been using my hazard signal to test the lights on the trailer. If I unplug the trailer, turn on the hazard lights and plug the trailer back in the lights work, if I tun them off and back on again with the trailer still plugged in they dont work.The tail lights work, but not the signal lights or the brake lights, I get the signal to the tralier light when I have the wire disconnected via a wire nut but voltage goes to zero when I reconnect it.I also ran all new wire for the trailer. Any help would be great.

asked by: Paul H

Expert Reply:

I have some suggestions to help troubleshoot your wiring issue with your 1990 Toyota Pickup and the Curt Harness # C55379.

Make sure your truck is running when you are testing the trailer lights, not just having the truck in the accessory mode. By having your truck running your trailer will be receiving maximum voltage because the alternator will be running.

Check your trailer connector with a circuit tester such as # PTW2993 to verify that you are receiving voltage on each pin. If you do not receive voltage on each pin, you will know where your problem lies.

If you know of another vehicle with a 4 way connector in working order, have them hook it up to your trailer and see if the results differ. This will help you determine if the problem is in your truck or your trailer.

You can run a jumper cable from the battery to each of the functions of the trailer to verify that each of the lights is working and receiving voltage. This is to determine if the voltage you are receiving from your vehicle is the issue.

On the connector portion, a pin may not be registering voltage if it is either bent or corroded inside the casing of the connector. You might want to check for either damaged or corroded pins within your connector.

Since you ran all new wire through the trailer, you might want to check to make sure that there is not a small cut or a possible frayed wire in one of the lines which is creating a shorting issue.

Lastly, I know you said that the grounds are on bare metal, but, you may want to check and make sure that the bare metal does not have rust which will interfere with signal. A rusty hitch ball can also prevent the trailer from grounding properly as well.

I have attached a FAQ regarding troubleshooting with wiring installations.

expert reply by: Lori W

Mark D.

6/28/2020

Trying to get the 55379 to work on my 98 Tacoma. The only way the trailer lights work is when I disconnect the connector from the truck lights (either the truck lights work or trailer lights work but never both together). Thanks

Chris R.

7/2/2020

I'm a little confused. Are you saying that the trailer lights DO work when disconnected from your Tacoma? I'm not sure where the harness would be getting power in this scenario.

Mark D.

7/2/2020

@ChrisR When I first connected the 55379 as per the instructions, only the truck lights worked. So I tried connecting the 55379 plugs only into the trailer plugs (my non-technical attempt at troubleshooting) then the trailer lights worked (but obviously not the truck lights). Update: I reattached my ground (aggressive sanding at the connection point) on the truck and all the lights work! Thanks!