Trailer Electrical Tester

**IntheGroove** · Feb 8, 2021, 09:51 PM

I needed a tester for working on electric parts on trailers. I didn't care for the commercially available units so I made one with parts I had on hand. Inside the box are two automatic-reset circuit breakers, one for the lights and one for the brakes. A 30 amp relay for the brakes. A solid state flasher. I mounted a voltmeter and a amp meter. The voltmeter will check the test battery or the battery on the trailer. The amp meter is for checking the brake coils.

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It will test all electric functions of a trailer, Lights, Brakes and Battery
I made a 25 foot extension for the trailer that can also be used on the tow vehicle with the plug-in tester so I can test from the driver's seat or under the hood where the fuses and relays generally are.

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Most trailers don't have backup lights put some trailers with surge brakes use a solenoid in reverse to stop the brakes from engaging, also will power-up backup cameras.