Info on trailer wiring ?

[adaviel]

I have a 91 Previa (Canada model).
I'm trying to wire up a trailer hitch connector (US/Canada 7-pin style), and wondered if anyone has any experience with this.
Well, actually, I'm most of the way through the job and was referred to this site from a more general forum, but I'd still be interested.
I found a bundle of unterminated wires behind the left rear light cluster that appear to be what I want, viz.
Green - Tail
Red - Left flasher
Brown - Right Flasher
Yellow - Reverse
Blue - Brake
Black - ??

I'm not sure what the black wire is - it does not seem to be a ground.
I was looking online for some confirmation of this wiring, but could only find a guide to installing a European trailer harness.

[timsrv]

To my knowledge there is no pre-wiring on the Previa for towing. There will be wires going to each light & these can be tapped. There are some differences in wire colors from Canadian to US models, so I won't go into colors. Just pull the tail lights & one by one turn on the lights. Ground is typically white with a black stripe, so the other wire going to the bulb you want is typically the power wire. For the 1157 bulbs you can use a test light to identify the one with power.

One thing to keep in mind is the Previa uses a "3 wire system" & most trailers use a "2 wire system". 3 wire systems have separate stop & turn lamps where the 2 wire systems will use the same lamps for both functions. Assuming the trailer has the normal 2-wire system, you will need a "3-2 wire tail light converter" (http://www.amazon.com/Curt-Manufacturing-58240-Light-Converter/dp/B001EP0GI6/ref=sr_1_4?ie=UTF8&qid=1377839406&sr=8-4&keywords=3-2+wire+converter). The simple converter shown in that link is adequate for trailers with single bulb circuits. If you are towing something that puts a bigger loads on the tow vehicle's electrical system, then it's better to use a "3-2 wire powered tail light converter" (http://www.amazon.com/Curt-56190-3-Wire-Powered-Converter/dp/B004IYB968/ref=sr_1_8?ie=UTF8&qid=1377839728&sr=8-8&keywords=3-2+wire+converter+powered). The powered converter is wired directly to the battery, then uses power from the light circuits only to trigger small relays. This essentially removes the load from the lighting circuit and puts it directly to the battery. This type of module will also give you brighter trailer lights.

If you are towing something that has electric brakes &/or needs a charge line, you will need to add those wires from scratch as Toyota makes no provisions for these. Tim

[Previologist]

I found this uHaul 3 to 2 converter on my van, and it looks quite sketchy. It seems swollen and one of the wires looks like it melted. I didn't realize this converter was was there when I wired up a new flat 4 harness to the wires that I know now come from the boogered converter output. The 4 wires were just cut off very short out of a plastic conduit and hanging exposed behind the hitch area (van came with an aftermarket hitch but I have never towed with it).

2 curious things about the old converter. As I said It looks bloated and possibly like it overheated. Is there actually electronics in these to overheat? The other curiosity is that it has 4 wires going in and 4 wires coming out, plus a 5th wire that skirts right past it (and does not emerge where the other 4 are cut off). 4 in and 4 out seems like an odd configuration for something called a "3 into 2". i"m guessing its a powered converter because it says "high energy", so perhaps it has fried electronics in it. I'm also guessing I will need to replace it before I can tow, but with my electrical problems, I'm concerned. But I'm trying not to get excited that it might be the cause of my problems.


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[timsrv]

Yours actually has 5 wires going in and 4 coming out. The "ground" and the "tail" are likely just wires traveling through the housing. Regardless of how many wires going in and out, the non-powered 3 - 2 wire converters always have one less wire coming out. That converter's job is to take the separate "stop" and "turn" circuits from the tow vehicle (referred to as a "3 wire") and convert to the single stop/turn circuits found on most trailers (known as a "2 wire").

The one in your pictures is not a powered converter as it would need a +12VDC input to power it up. And yes, that one definitely looks fried. The non-powered converters are generally not recommended for normal passenger vehicles as their towing circuits are only meant for single tail lights. The powered ones are best in these applications as they don't load up the tow vehicle lighting circuit. They take power directly from the battery, then route it to where it's needed based on the inputs from the tow vehicle.

The non-powered converters are basically just some diodes. The powered ones are a combination of diodes and relays. I've built these before from basic components, but considering the effort and the individual cost of components, it's better to just go buy a pre-made sealed unit and install......especially if it's going to live in a high humidity environment and/or be exposed to road spray.

BTW, I'd also recommend tracing all those wires back to the original connection points and replacing all the connectors. As bad as that converter looks I'm sure there is corrosion and bad connections. Always a good idea to use dielectric grease & seal your connection points with shrink tubing when they are exposed to the elements. Tim

[Previologist]

I only count 1,2,3,4....oh wait, 5, you're right! My thumb was hidden by my palm...

[Previologist]

I traced the converter wires to their source inside the left rear tail light, and found everything except the ground disconnected. There died my hope for an easy fix to my larger electrical issues. (On the bright side I have both inside rear panels off so I'm able to check all the grounds, which of course look perfect. I disconnected the rear speaker that was still present and working, because I don't want to go back in once I button it up. I am going to go with just 2 door speakers for simplicity of diagnosing audio issues, for now. )

That "extra" green wire actually is bent around from the van side to head toward the trailer harness with the other 4 exiting the trailer side of the converter...but only 4 wires, one green, emerge from the hitch end, so not sure what happens inside the conduit but it doesn't matter. I will replace whatever is in there.

The live cut ends at the tail light were all taped, but they are shown bare here. The brown wire seems to be hiding in this picture.

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With everything else I have to do in the next 2 weeks, and my electrical pulsing still extant, I'm not confident I'll be doing any towing with this vehicle soon. Using a powered converter will just compound the issue most likely.