What Vehicle Side Trailer Connector Pairs With Trailer 4-Flat Wishbone Wiring Harness
Updated 01/12/2026 | Published 08/28/2024
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Question:
Hello i was hoping you could help or give me insight but i have a boat trailer that has a 4 flat wishbone so it got 5 wires running to it. On i truck i have just a standard 4 wire flat connector. When i connect i get everything but running light , and Ive tried looking for a solution but nobody talks about the vehicle end. So my question would be what kind of plug do i need on my truck to get the running lights on the trailer working , thanks.
asked by: Austin
Expert Reply:
Hi Austin; the 4-flat on your truck is what you need. Since the running lights aren't working on your trailer something else is wrong and you will need to do some troubleshooting. The power from the running light circuit on the vehicle side 4-way should run to both running light wires on the trailer side since they're tied together through the 4-way.
Make sure the connectors on both are clean and undamaged. Assuming they're in good shape I would test for power on the vehicle side with a circuit tester # PTW2993. If you have power here the problem is on the trailer. If not, you need to check the vehicle wiring for a short or bad ground. If you find you need to replace the 4-way you can use the # C59236 assuming this is on your 1999 Silverado. If you have the factory connector then you can use the # C55515 instead.
On the trailer side start by checking your ground connection. After that, begin testing behind the connector and work your way back until you locate the problem and repair it. You can also replace it with the # A35W42B.
Product Page this Question was Asked From
35 Ft 4-Way Trailer Wiring Harness - Wishbone Style - 42" Ground
- Trailer Wiring
- Trailer Connectors
- Trailer End Connector
- 4 Flat
- Plug and Lead
- Optronics
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Robin H.
1/12/2026
Hey Austin, did testing the running light circuit with the circuit tester help you track down the issue on your boat trailer? Knowing what you found could really help others trying to troubleshoot a similar wiring setup.