2014 RAV4 - Towing electrics

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Sun 5 Jul 2020 21:36
2014 RAV4 - Towing electrics - jthan

My otherwise perfect (literally!) 2014 RAV4 has been prone to run down its battery prematurely since fitting towing electrics 4 or so years ago. It's only a minor inconvenience (as I now use a battery isolator when parking for extended periods) but ideally I would like to fix the issue one day.

Everything works as it should, and the electrics are Toyota's official kit (bought from Toyota and a plug in fit). However, the kit (despite being Toyota branded) was made by Westfalia, and I've recently noted on the internet that Westfalia acknowledge battery discharge problems with some of their towing relays where only a single 12v feed is used, instead of a permanent feed and a switched feed. I suspect (but am not certain) that the problem might be due to the Toyota installation using only a permanent feed.

In the past, I've fitted generic towing bypass relays to a number of cars (always with a 12v permanent feed taken back to the battery) and never had a problem with any, although the most recent of these was a 2004 C-class. I would be grateful for any thoughts on whether replacing the dedicated electrics kit with an old-fashioned generic bypass relay (powered straight from the battery) would be likely to cure the premature discharge? Or whether that would be unwise with modern electrics?

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Sun 5 Jul 2020 23:08
2014 RAV4 - Towing electrics - elekie&a/c doctor
I think I would want to check the actual battery drain first before condemning the tow bar kit . It is easy to isolate the kit to confirm your findings. If the Westfalia wiring Circuit can be altered, Then I guess this would be easy than a rewire with by pass relays . All the kits I’ve seen have a permanent supply from the battery with no problems. Are you using single or twin electric system, or 13 pin ?
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Mon 6 Jul 2020 19:37
2014 RAV4 - Towing electrics - jthan

Thank you for the rapid reply.

It's a traditional single 7 pin socket and the 12v feed was plug-in near the back of the car; no new wire to the battery.

I won't post a link to the Westfalia's information about battery drain, but putting 'Westfalia towing battery drain' into Google brings it up with the description 'Terminal 15 - Westfalia-Automotive'.

I appreciate the sense in doing a bit of checking next. On the other hand, using the isolator means it's not a major issue to me and I'm reluctant to strip out the boot linings again unless I'm fairly confident that this is likely to be the issue.

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Mon 6 Jul 2020 20:12
2014 RAV4 - Towing electrics - Ian D
If it is the towbar electrics maybe you can fit an isolator to the towbar electrics 12v feed and only switch on when you are using the towbar...
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Sun 30 Aug 2020 21:14
2014 RAV4 - Towing electrics - jthan

Elekie doctor's comments appear to have been spot on.

I did a bit of experimentation today and found no evidence of a problem with the towing electrics - or anything else for that matter! After a settling down period (around 20 minutes), residual current was only about 20mA. It jumped up to (and stayed at) around 500mA with the key fob close to a front door, and it settled around 200mA with the key a few feet further away. With the key taken completely away, it dropped to around 160mA for perhaps 20 minutes; then falling to about 20mA, where it stayed indefinitely (unless I brought the key back, or opened or closed the bonnet latch - then temporarily back to 500mA, etc).

Pulling the towing fuses had no effect at all (although pulling the dome fuse at the 160mA level immediately took the current down to 90mA).

So I'm thinking now that perhaps the only problem is that I don't drive it enough (which, by any normal measure, is true) and that the battery cutoff switch I fitted a couple of years ago is the right solution.

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