Trailer Light Conundrum

Hey folks,

I have a bit of a conundrum with my attempt to hook up my new trailer lights to my 1998 Hiace AWD KZH138 campervan.

The new trailer has a 4 way flat hookup and the JDM electric hookup on the Hiace is a 7 round pin. I bought a standard (for North America) 7 pin to 4 pin adapter and all the lights on the trailer work (running lights, left turn & right turn signals) except for the brake lights.

It's a head scratcher as the adapter retailer (and everyone else that I have spoken to) insist that the brake lights share the connection with the left/right turn signal wires - in other words, if the turn signals work then the brake lights should work as well.

All the fuses in the Hiace show as good, although I have not found a dedicated trailer electrics fuse.

I came across the schematic below which seems to show the brake lights on a separate pin altogether (lower center pin) - if this is indeed the hookup that was installed in JDM then my adapter will not 'capture' the brake light signal.

Has anyone else come across this issue and, if so, how did you resolve it?

Cheers for any help or suggestions.

Yes you will need some logic circuitry to mix in the brake signal, I think you US folks are the only ones in the world who double-up the function of brake and indicator lamps. I'm not sure if a few diodes would do it as I'm not quite sure how your system works; how do the turn indicators work when the brake is applied? I don't think your system is even legal here although I could be wrong on that.

The issue would seem to be incompatibility between the JDM trailer electrical hookup and the US manufactured trailer. Brakes and turn signals work fine on the van, I may just have to have the van trailer electrics rewired to solve this.

That would be the easiest route. It could likely be done with a few relays but you still wouldn't have the correct operation of the lights and the turn signal lamps would be the wrong colour (here they must be orange or yellow while the stop lights must be red).
Nice LED lamp assemblies are cheap and a bit of multicore cable won't cost much.

I have a KZH. I found the trailer plug wiring was piggybacked off brake /turn/tail wiring high up behind a panel driver side above rear vent. Ditch your idea of using an adaptor. Disconnect wiring at JDM plug. Get a $4 12v test bulb tool. Connect to your preferred US/AU towbar plug....using your 12v test bulb tool.

@geoffreyKZH138V there is nothing wrong with his connector or how it's wired, it's just that he is trying to adapt to the odd US system where brake lights are shared with the direction indicators. We all use a 4 wire system as does his van, they use a 3 wire system which is what his trailer currently has. There is no way of directly connecting the trailer to the van, some relay or electronic logic is required to make the conversion. Rewiring the trailer to 4 wire and replacing the lamps with nice new LED fittings is the way to go.

Here is a circuit published way back in March 1982 for doing the conversion.
There are many reasons it would not be advisable to copy this now (things the author overlooked and much better devices now available) but it shows the technique.

Many thanks for the assistance, I've got the Hiace at the shop to sort this one out. There are some corroded wires that might be the culprit here.

Just wanted to update with the final outcome: corroded wires were replaced and the problem was not solved, the 7 way electrical trailer hookup just would not send the brake light information to the 4 way North American trailer hookup - likely because of the difference in the way trailer brake lights are wired in Japan vs North America.

The simple solution was to add a second trailer electric hookup on the Hiace, this one a standard North American 4 way hookup that works fine with my new trailer. No problems since then.

Quick intro and 1st post.

Hi, I have a 1998 KZH100 SC G 2BY FC43.


Wanted to add this to the posts for others to find for future wiring needs. UHaul carries a 3 to 2 wire taillight converter for $20 that are needed to install for trailers.


It seems I can't post links for 7 days, so here's the information, just correct the www to view information.

w ww.uhaul.com/MovingSupplies/Wiring-Lights/Tow-Vehicle-Wiring/U-Haul-4-Way-Flat/?id=13684