Coupler Switch Backwards?

[Longhair]

When I hook the trailer up, the truck makes the hitching sound and then goes twice as fast than it did without the trailer.

I thought I had the coupler switch in backwards, so I took it a part only to see it only goes in one way. During bench testing, I had the trottle in 2nd gear and triggered the coupler to simulate the trailer on there only to see the rear wheels speed up until I released the coupler switch. I should add that the sounds also change from an engine with a load (no trailer) to an engine without a load (trailer).

I also switch the green & black wires in the plug and that didn't make any difference.

What can I do to fix this problem?

[Mouton]

The first part of your post describes how the switch is supposed to work. The switch itself just closes as circuit and its cables have no polarity.

What puzzles me is your last observation, that the sound changed from an engine with load to an engine without load when you hooked up the trailer. Is that correct? If so, with all due respect are you really sure about that?
It would indicate a problem with your unit as there is no way the user can create this behaviour. When it goes twice as fast it believes it has a trailer hooked up, if to makes the wrong sound to you it might need to be checked by a Tamiya representative.

[Longhair]

I figured every thing out - the engine sounds were due from the shifter servo being reversed (what I thought was low gear was high gear).

What puzzles me is why the truck would go 2x as fast with a trailer attached than without a trailer attached.

[hydroliftT17]

It’s because the truck need more power when it’s running with a heavy trailer. And for some reason Tamiya felt that we could not control the tractor with “all” that speed when running without a trailer, so they slowed it down. Which is kind of dumb when running an 80T lathe motor… as I’m backing up without a trailer, I have to use 3. Gear :P

[Mouton]

Longhair, glad you worked it out. Reversed servos can play a trick on you since the manuals do not state that servos can move in opposite direction when hooked up to the exact same receiver and transmitter. Futaba and hitec, to mention two manuafacturers, move in opposite directions, thus creating confusion for those who think that everything should be in order.

hydrolift, neither these trucks, nor the MFU were designed for 80T lathe motors...

Keep in mind that it also changes the engine sound and makes it sound a bit more strained when a trailer is hooked up.