95 towbar wiring

You should be good to go as is if the trailer has the European lighting system (separate turn indicator wiring) and it only has one set of lights. With the U.S. system I use a simple converter for our small boat trailer. A relay is called for if the trailer has electric brakes. One should not be pulling such trailers with a Saab in any case.

The tow bar wiring in my 95 is spliced into the existing rear lights wiring, without any relays.

The only 'problem' is that I connected +12 V to the free contact on the 7 position plug (to have 12 V in a caravan), but then on trailers with a rear fog light that light comes on.

First question: do you have a "95" or a "1995" or a "9~5" ?

Ahh, it's a 2002 "95", uk spec. What's a "9~5" ?

It's not quite a trailer - a bike carrier with lighting board. So yes, just one set of lights. Separate indicator wiring? Oh, US indicators flash the brake lights?

Either way, no need to worry about bulb checking circuitry or suchlike then? I've read somewhere that there's supposed to be a buzzer in the car to show the indicators are working (european legislation i suppose). Can anyone enlighten me on this, and whether the saab "pre-wiring" addresses this?

Maybe it is better written as 9^5 (=59049), as superscript is a bit difficult to write directly in plain text :-)

Ooops, it was displayed correctly in my newsreader, but the quoting seems to change it back to the original text.

That's one way to distinguish a (9~5) "nine-five" from a ('95) nineteen ninety five model year or the original (95) model ninety five from days gone by.

To answer your question, I don't see any reason from an electrical viewpoint that you can't tap off the rear lights but you should use a relay and grab power from the fusebox - not from the existing lights.

ahha, didn't know there was an previous model of the same "name".

Seems reasonable. Thing is that I don't need to tap into the wiring, 'cos there's already this "pre-wiring" which terminates in a socket by the spare wheel apparently ready for the tow-bar electrics. What I don't know is whether this is simply a tap into the loom as you describe, or whether it's altogether better (eg. already a relay inline etc).

relay for rear lighting on a trailer.. Relays are only used when a power supply is needed for a caravan fridge, etc. The relay only works when the engine is running to avoid a flat battery if you forget to switch off the appliance when the car is stopped. A relay for the connection between the car lights and the trailer lights could be dangerous if it failed plus why have a relay there anyway?

Yes, you *do* use a relay. You do it because the cars existing wiring is only designed to handle a certain amount of current. The relay allows you to add only a minor amount of flow to the existing circuit and then the relay handles the load of the new lights.

This is particularly important in a recent Saab since most of the wiring passes through a computer that controls all lighting. Overloading it is a really bad idea.

As to reliability - you are seriously endangering it by not using a relay. The relay itself will be very reliable and last the life of the car. If you are concerned about failure, you could rig a "light failure" detector to the new circuits but I think it's overkill.

I have just fitted a factory supplied tow bar and its electrical lighting equipment to a two year old Land Rover. The wiring for the trailer lights did not pass through a relay ( or do you mean some type of fuse). I am not familar with the Saab in question but as on the three previous tow bars I have fitted no relay for the lights. What type of relay do you mean, I am interested in a relay of the type you suggest. If the trailer lights overload the cars lighting circuit it will operate an existing fuse.

So does the "pre-wiring" or whatever it is, sitting in the spare wheel compartment ready to be plugged into, already make allowance for this? The saab garage parts counter seemed to think the saab "wiring harness kit" or whatever it is, was essentially just a plug and wires.

Where can I get hold of a wiring diagram for the car ?

rgds, g.

One would have to assume that the later cars do have this engineered in if they have a connector you can plug into. If it's really just a wire and plug then it's pre-designed for the additional flow. I believe the kits for the NG900 and 9~3 include a specific tap that goes back to the fusebox to pick up the power. But, your car may be different.

You can usually purchase Saab manuals on specific aspects (electrical) of the car from the dealer. I'm not sure if they have changed that since going to CD based formats.

You could use any standard automotive relay. But, as I see it, you would need four - one would relay the brake lights, one for the parking lights, and one each for the turn signals. You would have one power source from the fuse box feeding all four but the trigger would be a tap from each of the other circuits.

I would assume that a Saab kit would include a module that would handle all this. I've never seen their kits.Depending on the current flow, they might be able to do it with a solid state module. Or perhaps someone with circuit knowledge would be able to design that.

However, I do know that the wiring for the current lights is fed from an Integrated Electronics module and I would not be comfortable pulling additional power through that.

Talk to the towbar people or the vehicle maker and use the prewired harness they recommend. This is what everyone uses with no problems. The towbar will be specific for the car model likewise the wiring harness. I don't know how competent you are but some people struggle to fit towbars, a lot depends on the vehicle. Generally the towbar supplied by the car maker is easier to fit than cheaper ones.