Rx400h towing module

[welland]

Yesterday I was checking the wiring to the trailer sockets on my rx400h, which had been fitted some years ago by a previous owner.  I discovered that they were wired into bypass relays that had been spliced into the car's wiring loom.

It just made me wonder about how the electrics work on my car. 

1)Does it have a canbus system?

2) if yes, is there a canbus towing module available?

3) if yes,  aside from the method of connection to the car, what functional improvements does it offer over the  conventional bypass relays?

 

Regards Peter

[Gliderpilot]

I fitted my towbar myself and it was a pain to get the wiring correct. Lexus do sell a kit for the electronics but it doesn't just plug in there is quite a lot of splices to do. Lexus don't have their own towbar but buy in bars from Westfalia and re-badge them, these come with a wiring kit which has a control box. One of the function includes a rear fog light baypass. When you switch on the rear fogs you are supposed to switch them off again strait away but because the main lights are on the trailer fogs will stay on. I've included the instructions for the Lexus electrical kit. To be honest if your electrics are working OK it's not worth changing them. Although there is a CAN BUS on the 400h it doesn't help with the towing electrics.

RX Towbar electrics.pdf

[sando63]

Hello Peter, (Gliderpilot)

I hope you are still towing them large Bailey caravans ? I have read your topic on towing, and one or two say the max nose weight is 80 kg, which I agree.

But nobody says anything about going over the weight, apart from it will cause damage to your rear electric motor. My caravan tows like a pig with 80 kg,

but with 90 kg it's spot on, getting to the point, Do I or Don't I ?, Surely these Lexus Rx400h's can handle 10 kg extra. Also I have my boot loaded to keep

the weight out of the caravan ! I do use spring assistors,  ( appologies for spelling ). Cheer's Peter,

Regards Dave.

[Britprius]

I tow with a 2007 GS450H, and this probably has the same basic lighting system as the RX400H. I wired the electrics myself as the Lexus module was expensive, and still not plug, and play.

I used a bank of 12 volt relays in a plastic box, coils operated from the rear lights, with the contacts fed via a suitable fuses from the 12 volt Battery very conveniently fitted in the boot of the GS. This not only works well for the lighting, but also gives split charging to the caravan Battery with 12 volt fridge operation when the car is in ready mode, and on the move.

It is important for my van to have a fully charged 12 volt Battery because being disabled I have a remote control motor mover fitted to the van. This essential for parking at home, and very useful on site especially as I can drive the van up to the cars tow ball without risking damage to the car bumper.

John.

[Gliderpilot]

On 5/31/2018 at 1:31 PM, sando63 said:

Hello Peter, (Gliderpilot)

I hope you are still towing them large Bailey caravans ? I have read your topic on towing, and one or two say the max nose weight is 80 kg, which I agree.

But nobody says anything about going over the weight, apart from it will cause damage to your rear electric motor. My caravan tows like a pig with 80 kg,

but with 90 kg it's spot on, getting to the point, Do I or Don't I ?, Surely these Lexus Rx400h's can handle 10 kg extra. Also I have my boot loaded to keep

the weight out of the caravan ! I do use spring assistors,  ( appologies for spelling ). Cheer's Peter,

Regards Dave.

No spring assisters and I've not checked the nose weight All I know is that it tows OK up to 60  70 mph. I normally tow at an indicated 60 on cruise control. It's quite solid at that speed. I've heard it said that the 80 Kg limit is because of the strain on the rear motor, I don't see it though, rear suspension yes but the motor doesn't bear any weight just torque when needed which is not very often on a motorway. I stand to be corrected though.

[welland]

On 5/31/2018 at 6:21 PM, Britprius said:

I tow with a 2007 GS450H, and this probably has the same basic lighting system as the RX400H. I wired the electrics myself as the Lexus module was expensive, and still not plug, and play.

I used a bank of 12 volt relays in a plastic box, coils operated from the rear lights, with the contacts fed via a suitable fuses from the 12 volt battery very conveniently fitted in the boot of the GS. This not only works well for the lighting, but also gives split charging to the caravan battery with 12 volt fridge operation when the car is in ready mode, and on the move.

It is important for my van to have a fully charged 12 volt battery because being disabled I have a remote control motor mover fitted to the van. This essential for parking at home, and very useful on site especially as I can drive the van up to the cars tow ball without risking damage to the car bumper.

John.

Hi John,

Sounds interesting..... Did you assemble your array of relays yourself,  or was it purchased as a kit for this purpose?

[Britprius]

12 hours ago, welland said:

Hi John,

Sounds interesting..... Did you assemble your array of relays yourself,  or was it purchased as a kit for this purpose?

I assembled the array of relays myself  quite a simple process. FET transistors could be used just as well to reduce size, but I used what I had at hand, and space to mount the box by the 12 volt Battery is plentiful.
The indicator circuit does require some visual or audible warning of bulb failure on the trailer. This was accomplished by fitting 2 diodes in series in the supply to the indicator relays, and a piezo crystal beeper wired across them. Mounted the beeper up by the woofer speaker so that it could be heard in the car, but not needing a long wiring run. The voltage drop across the two diodes is enough to drive the beeper without reducing the light output significantly at the bulbs.
If you need a circuit diagram I can draw one up. Just ask.

John.