The following procedure will allow you to easily add the necessary wiring and connector to your Miata for towing a trailer.
Tools necessary for installation:
Instructions (click on wiring diagram at right)
I've discontinued using converters for Miata trailer's lights. Doing that adds simplicity and dependability for NA Miatas, and most likely others as well.
After hours of use on long highway drives I've had two different brands of converters fail. An engineering evaluation of a similar third one revealed it was also destined to thermally fail destructively over time from being electrically loaded by my trailer's regular full-size automotive type lamps. My trailer is larger than those small tire-hauling type trailers with their small light duty lighting.
To completely resolve a converter failure from possibly ever being a problem again, I just discontinued using one. Instead I installed a set of dedicated turn signal lights on my trailer.
With those and other trailer lighting circuits no longer shared ones, they can then all be individually directly connected to Miata's rear lighting that's all individual separate circuits too. Unlike turn signal flashers used in some other type cars, Miatas use an isolating relay; so, there's no disruption of the Miata's (relay controlled) turn signal flash rate (also for Hazard flashers too).
All the Miata's fuses used for its rear lighting have more than ample electrical reserve capacity for the additional load for trailer lighting, even if full-size regular automotive type lamps are used. Without a trailer light converter if there is an electrical short a car fuse will blow, instead of the predictable risk of the more expensive electronic trailer light converter blowing, and possibly the car fuse blowing too. So, there's no problem at all by just directly connecting all separate-circuit trailer lights in parallel with the Miata's rear lighting circuits. I also discovered it's more cost effective to add the dedicated set of turn signal lamps than a trailer light converter.
The wiring for rear lighting in the NA Miata's trunk (perhaps others too) is in a cable that's run up high just under the car's left side quarter panel. Making connections up there helps keep electrical splice joints out of harm's way.
The car's wiring:
Taillight ..... red/black
Stoplight ..... green
Right Turn .... green/white
Left Turn ..... green/black
Backup ........ red/green
Ground ........ car's metal body
Add a plug-in length of cable for use in extending out of the trunk to connect the trailer. When the cable is not in use it can be nicely stored by simply shoving its end, and most of its length, into the NA Miata trunk's rear trim panel end-opening on the left side.
I've not found selecting the type of trailer plug-in connector to be at all critical. The best way I've found to decide which type to select is by looking at what others I know use so that our trailers can be plug-in compatible with both of our cars.
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29 December, 2007