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Old 10-06-2003, 03:14 AM   #1
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Default Trailer Wiring

Grettings! I am a new user to this site. I've been viewing it for quite a while, but never had occasion to post a question. Thanks to all for their contributions.

I have a '95 SSEi. It has the little diagram on the dash board that shows which lights are out when a bulb is bad. I have a trailer hitch on this car and had planned to use it to tow two snowmobiles. I have wired many vehicles over the years, and I think I know what I'm doing but I have spent between 6-8 hours messing with this car to try and get the trailer lights to work. No luck so far.

I bought one of those trailer wire converters that use 12 volts to power it to isolate the trailer wiring from the car but I still get indicator lights showing that I have bulbs out, when in fact I do not have any bulbs out. It also causes the lights to flash REAL slow when I have it hooked up to the trailer. It also seems to make the headlights dim.

Has anybody ever wired a 95 SSEi for a trailer and had success? The shop where I had the hitch installed said they could do it for $250.00. They said they can wire this Bonneville, but it takes a lot more work. They wouldn't tell me how or what kind of extra work it takes to get it to work correctly. Any help is greatly appreciated.
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Old 10-06-2003, 10:01 AM   #2
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I'm the only one here that has a hitch and wiring (besides Terminator, who isn't here much or lately).

I would strongly advise against towing 2 snowmobiles with your SSEi. Granted, it'll be winter, with cooler trans temps, but still not a good idea. What'* the total weight, including the trailer?

The trans is the weak point in your drivetrain, and towing with a FWD is generally not a good idea. I tow a light utility trailer occassionally.

For my wiring, I did just the parking lights and brake lights. Wired directly to the lighting circuit, and my lamp monitor has no problems at all. For your problem, if you plan on using the isolator, I'd be tempted to run a dedicated circuit directly from the battery to power it. Where are you getting power now?
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Old 10-06-2003, 04:31 PM   #3
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wow 250 bones, thats way too much to pay someone to do trailer wiring.

i did the wiring myself cuz i tow a custom build trailer, i also just tapped into the brake lights and backup lights. i dont see how your DIC would know if there was some extra load from the trailer lighting.

if you do want to isolate the wiring from the car, i agree with running a dedicated hot wire from the battery. what you could do then is wire some SPST relays in, using a signal from your brake lights and back up lights to power the coils on the relays. that may do the trick.
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Old 10-06-2003, 06:05 PM   #4
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Quote:
Originally Posted by greyfaux89LE
wow 250 bones, thats way too much to pay someone to do trailer wiring.
Yeah, I think they didn't really want the job.

Quote:
i did the wiring myself cuz i tow a custom build trailer, i also just tapped into the brake lights and backup lights. i dont see how your DIC would know if there was some extra load from the trailer lighting.
Actually it'* the Adaptive Lamp Monitor Unit that watches current flow to the bulbs; the DIC is used simply to display a warning whenever the ALU finds something to complain about. I'm not sure what the problem is with your installation if the connections were done properly, but when you talk about dimming headlights I get a little worried, because the headlights should have _nothing_ to do with trailer wiring, and the headlight circuits don't need to be touched. I'm thinking somebody botched something there.

A basic trailer wiring harness has four circuits: Brown (taillamps), Green (Right brake/turn), Yellow (Left brake/turn) and Black (ground). You only need to access four circuits in your Bonneville, all of which are at the back of the car already: taillamps, brake lamps, left turn signal and right turn signal.

Note that if your trailer has only one brake/turn bulb on each side, you'll need a logic module in the circuit (either in the trailer harness or added to the car trunk wiring) that will interrupt the trailer brake lamps on the signalling side, since the trailer will be using the same bulbs to signal both braking and turns. You cannot simply connect a brake lamp feed and a left-turn feed to the trailer lamp on one side, and another brake lamp feed and right-turn feed to the lamp on the other, because you'll be bridging your brake lamps to your turn-signals that way and your ALU will start screaming bloody murder. If dealing with the separate amber turn signals of the Bonneville is too confusing for hookup to the trailer, just skip it and focus on getting your taillamp and brakelamp circuits working.

Quote:
if you do want to isolate the wiring from the car, i agree with running a dedicated hot wire from the battery. what you could do then is wire some SPST relays in, using a signal from your brake lights and back up lights to power the coils on the relays. that may do the trick.
Sounds reasonable.

What the ALU is reacting to when it gives a warning is a dropoff in power consumption on a lighting circuit or (I think) an imbalance between bulbs on either side. It might be a bad or intermittent connection that'* provoking it, or (in this case) an inadvertent connection between the brake lamp circuit and the turn signals. I know the service manual has some useful explanation on what triggers the warnings but it'* been a while since I looked at that.

In any case, if your headlamps are dimming at any time, somebody has screwed something up; adding trailer lights to the wiring is not brain surgery.
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Old 10-07-2003, 02:24 AM   #5
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Thanks to all who responded!

I think the trailer & sleds would be around 1300 pounds. Maybe you're right. It might be too heavy. I've had a few other people tell me I shouldn't tow with an SSEi. I just don't want to buy another vehicle just to tow my sleds.

Also, I'll admit I really didn't do it correctly. For the power to the converter, I just tapped into the running lights, so actually I would only have trailer lights when those were on. I think I will have to wire it directly to the battery if I chose to use this car to tow the sleds.

A comment was made about SPST relays. I don't know what those are.
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Old 10-07-2003, 02:42 AM   #6
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Single pole, single throw. Just a relay. Use low voltage to switch high voltage.
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Old 10-07-2003, 10:38 AM   #7
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Quote:
Originally Posted by Brutus
Thanks to all who responded!

I think the trailer & sleds would be around 1300 pounds. Maybe you're right. It might be too heavy. I've had a few other people tell me I shouldn't tow with an SSEi. I just don't want to buy another vehicle just to tow my sleds.
Part of it involves properly balancing the trailer so you don't have too much weight on the tongue. The car shouldn't go nose-up when you attach the trailer (and even though an SSE/SSEi with ELC will use its rear air suspension to level itself again, you'd still be loading it improperly that way).

The other part involves inertia and whether you're adding too much mass for the car'* own brakes to stop it safely. I don't recall whether you said the trailer has its own electric brakes as well.

Quote:
Also, I'll admit I really didn't do it correctly. For the power to the converter, I just tapped into the running lights, so actually I would only have trailer lights when those were on. I think I will have to wire it directly to the battery if I chose to use this car to tow the sleds.
I think you'll be fine with the connections you have available in the trunk for tailllamp and braking, as long as you do those right. As I said, your biggest headache will be dealing with the likely mismatch between the car, which uses separate bulbs for turn signals, and the trailer, which (probably) does not. You'll need to either add a logic module to your trailer connections for this (they're cheap) or just ignore the turn-signal connections altogether, whatever you prefer.

Quote:
A comment was made about SPST relays. I don't know what those are.
Single-pole single-throw relays, although if you're just adding a simple trailer with one brake lamp on each side and a couple of marker lights, I'm not sure relays would be needed, since I don't think a simple trailer harness would exceed the capacity of the car'* own lighting circuits.

The general idea with relays is that the trailer would have a separate power supply for its lights, and those lights would be turned on by relays that were triggered by the car'* own lights. If you had a honkin' big trailer with multiple brake lights and markers all over the place, this might be an issue, but a snowmobile-sized job with one big red bulb on each back corner wouldn't need that setup.
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Old 10-07-2003, 12:40 PM   #8
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Quote:
Originally Posted by willwren
Use low voltage to switch high voltage.
Or low current to switch high current.
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Old 10-07-2003, 12:54 PM   #9
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Yup. Using over-simple terms for the......never mind!
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