connecting a trailer harness to a late model car

With my '95 Lebaron, I just connected the trailer harness to the tail and turn signal lights directly** and there was no problem.
Everything worked.
But with late model cars, there are all sorts of extra parts (sensors etc.) between the tail light and turn signal switches and the respective light bulb filaments. Is there ever a possibiltiy of overloading any of these parts, by doubling the load on them, by connecting the trailer lights in parallel with the car's rear lights?
Or can I just attach the harness straight to wires that go straight to the bulbs?
Especially on a 2000 Toyota, which has a bunch of these extra parts.
**well, I used diodes to separate left from right brake/turn signal lights, but that's irrelevant here.
I'm especially concerned because I think I damaged my previous car's alarm by connecting the trunk in parallel with the door locks, instead of adding another relay. I would have thought if the output could handle door lock solenoids on both sides, it could handle the trunk solenoid too, but it seems it couldn't. (I"m going to send that back to the manufacturer to be reset, and maybe that will fix it, but maybe it's burned out.)
Thanks
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On 07/28/2012 07:54 AM, micky wrote:

a lot of modern cars have connectors for trailer lights already built in. you simply buy the appropriate harness and plug it in. check under the carpet in the trunk for a "spare" connector.
--
fact check required

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That's amazing. I posted earlier that if people knew how easy it was to add a hitch, they might sell a lot more hitches, but in a year since I bought this car, I've only seen 6 passenger cars with hitches, 3 of them at a ham radio hamfest. So they add t he wiring but don't publicize how easy it is to add a hitch.

I've been under the carpet, and there is no connector. Thanks anyhow, really. .
Also I thought this was relevant until I read your post a second time, this car had no trailer hitch, and was owned by a little old lady (I think. I have reason to believe what the car dealer told me.) . .
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I have a "Hidden Hitch" on my '99 Camry 4-cyl. The hitch is rated I think, at 2500 lbs. The Camry with automatic is rated to pull 1500 lbs. If I remember correctly, I had Googled for trailer wiring harness for that model car. I was able to buy a plugin harness. It plugged in right before the right taillight. I run the trailer with the headlights on so the trailer can be seen easier. Before I start driving I walk around the car and trailer to see if every light is on. Been working great for years.
I pull a 4 x 8 flatbed trailer. The car users' manual states to run a trailer with the Overdrive switched off. That precludes any long distance pulling, but overall works out fine locally.

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wrote:

Do you remember if the harnes require attaching a wire to ground somwhere, or if the ground was IN the harness?
I didn't want to spend the money for plug-in when doing it myself only involves soldering 3 wires and finding a ground somewhere.

Good idea.

I see it does say that in the 2000 manual also, to prevent overheating iirc,, but I think that may be an overwarNing. (not overwarMing) Once the car is going 60, it's good to be in the highest gear I think, and elsewhere in the same manual it says to use overdrive except in some limited circumstances.
To get to 60, I just accelerate more slowly than I would without a trailer (previous car, but also a 4-speed automatic. There's nothing about overdrive that would be different here)
The trailer provides more drag, but I think it's the speed the car is going that matters most which gear one should be in. At the least this deserves more inquiry.
The previous car, a LeBaron, only accepted a class I hitch which is rated only for 500? pounds. All I had was a simple Harbor Freight 4x8' trailer and a bedroom dresser on it, but I went from Dallas to Baltimore with no trouble. Didn't even realize it was there most of the time. I didn't take xways much, but that's because xways are boring, and I like to see towns and cities. And I can still do 60 most of the time on US Highways that arent' limited access. . On the xway the only thing to see is trees and it's too easy to get up to 70mph without noticing.
The tach should have interesting info too. If it's barely any higher at cruising speed with the trailer than without, I think that means overdrive woudl be okay.
Anyhow, I think it also matters if one has 300 pounds behind him or a traler and 1500 pounds. The lighter the load the farther I would go.

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There was no need to attach a separate ground wire. It was all in the plugin harness. I paid less then $20.00, I think. I don't remember the exact figure anymore.

I think the 4th gear, Overdrive, is activated through electromechanical components (?). I'm afraid I might stress the electronic components if I use the OD with the trailer. Anyone have any other ideas if that could be a problem? :-)
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wrote:

Thanks. I'll look harder for the ground. That would be easier than finding a screw. It's been hot here for months, but it's cooling off some and for sure by September it will be nice out.
I even went to U-Haul to check one kind of connector they used, so I could install the matching one on my car (and also on my old flatbed trailer, which I pretty much gave to a friend, but the thin wiring got ruined while he was using it. )
FWIW I'malso planning to replace that trailer's wiring with the same connector that U-Haul uses, or maybe to put two kinds of connector in my car, so I can use my old trailer sometimes, if only to haul my friends building scrap to my friend's dumpster at his business. He used to have his carpenter do that, but the carpenter quit or got a truck without a hitch.) . ....

LIke a solenoid? Something to pull or release a transmission band?

When you press the button on the shift lever, the signal might go to an ECU, an electronic control unit. Just about everything does these days, even in my 2000 Solara, but the load on the ECU to control a solenoid or any other electromechanical part would no greater no matter what. Not if the trailer were heavier, not if the temperature were higher, not if the engine was not working well. And the load on the solenoid would be no greater. The transmission ECU waits until certain conditions are fulfilled before it upshifts (or downshifts) and one is that the car is -- I don't know how to describe it, but the transmission is designed to shift at the same time a person would shift a manual transmission. If you're accelerating and then back off the acc. pedal, it should upshift then. If you don't back off the pedal it shifs when the car speed is at a certain point for each gear it could be in.
These days, when tthe computer could do it, the car itself could actually relent on t he acceleration for the couple seconds it takes to shift,, but I don't know if cars do that.
The only thing they could be talking about is not the shifting into gear but the running at the high gear.
You know, if you put three 200-pound passengers in your car, that would be the same as towing 600 more pounds, (except for the extra drag that a trailer adds. But the drag a trailer adds depends on the size and shape of the load, not its weight. ) but most people towing only have no one or one other smaller person in the car.

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wrote:

to check *what* kind of connector they used.

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micky wrote:

First find out if the vehicle even has a tow rating. Many newer cars don't. They are just not built heavy enough to handle even small trailers. If it does have a tow rating then there should be a direct fit harness IF it's a popular vehicle. Most of those plug into a connection underneath the vehicle, usually either a separate connector or inline with the rear lights. Depending on the model the harness may be nothing more than some wire, or it could be a mess of relays and add-ons that you need to supply power and ground to carry the load of the lights.
--
Steve W.

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On 07/28/2012 06:26 PM, Steve W. wrote:

popular myth, usually completely untrue.
<http://www.thetruthaboutcars.com/2008/02/the-great-american-anti-towing-conspiracy/
many vehicles sold in other markets have rated capacities which can be substantial, but zero here in the u.s. even from u.s. manufacturers like frod and g.m. that sell in europe with towing capacities, but don't rate the same vehicle here. the festiva for example.

if it doesn't have a built-in connector, you can often get a "t" connector if you look hard enough. it sits between the existing light sockets, and the harness, and takes care of all the connections without cutting or splicing. they usually also split two-color brake and turn signals into the combined red brake/turn used on trailers.
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jim beam wrote:

<http://www.thetruthaboutcars.com/2008/02/the-great-american-anti-towing-conspiracy/
Opinion piece in which the author himself demonstrates why vehicle tow ratings matter.

Doesn't matter what the vehicle may be rated in other countries. What matters is what it is rated for in the location it is used.

That would be the inline type I mentioned. You have to make sure that the vehicle can actually handle the load though. I have seen more than a few problems created from the extra light loading.
--
Steve W.

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On 07/29/2012 03:37 AM, Steve W. wrote:

with respect to legal ratings, agreed, but with respect to engineering ratings, it makes no sense. thus i'm questioning the origin of those legal ratings.
fact is, and i've lived in europe so i've seen this first hand, they use cars for towing all the time. and that's in a place where they have legal restrictions up the wazoo, much worse than here.
the notion that seems to be unquestioningly accepted here, that you need a honking great truck to tow something like a jet ski, let alone a camping trailer, is just bizarre in engineering terms. the only real difference in "capacity" there vs. here, is that almost all light trailers there are braked. here, few are, and if they are, they're usually electric, which is another bizarre anachronism we have given that they don't modulate.
now, if a trailer is unbraked [which i think is retarded since it really messes with dynamics] then sure, a larger heavier towing vehicle makes some degree of sense, kinda. but to blindly and unquestioningly swallow the garbage fed us that a car rated in europe for 3000lbs isn't qualified to tow here is utterly ridiculous.

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Please, all, forigve me for taking so long to get back to you.

Thanks. There aren't many cars I will buy since they have to be a convertible. Before I started shopping, I made sure there was a hitch made for the Solara. I was pleased that it was class II instead of class I like the Lebaron took.

I'll take a look.

Very interesting. If I had two cars, maybe one would be a little sports car, but since I only have one, it's the biggest late model convertible I can find, not counting the Rolls Royce. I woulld like to marry a girl with a pickup truck, but the odds are against it.

Underneath. I admit, I only looked in the trunk, not there. Well, I've looked there but not when I was specifically looking for a connector. My bet is that this is mostly true for trucks and SUVs. Do they really do this for passenger cars? I'll look again when it's not so hot out.
(I've read that trailer hitches used to be a truly optional accessory on SUV's but that they are thrown in almost all the time now by dealers, and if they're going to do that, might as well pre-wire them. OTOH, I've looked for a year now at passenger cars and only seen 6 with trailer hitches, 3 of which were at a ham-radio swap meet. There are probably more in western Maryland and maybe more even farther west. )

Relays would actually be good. If the tail lights are powered by relays, any overload created by the trailer lights would at most damage the relay (but it wouldn't) compared to output straight from some microprocessor, where an overload can damage a transistor in an integrated circuit. An IC that does 20 other things and costs a lot of money to replace. The remedy a taillight powered straight from a microprocessor is to use a relay whose primary doesn't draw much more current than the taillight did (and most won't. Certainly the ones made for autos and auto burglar alarms won't) and connect both the taillight and the trailer taillight to the secondary of the relay.

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