adding alarm trunk protection to a pontia

I own a 1999 Pontiac Sunfire. Recently I added a K-9 Mundial-SS/LA car alarm. The technician that installed it, told me that he can not protect the trunk unless he put a "pin switch" in the back. (I did not want him to drill any part of the trunk because I don't want any water leak in the future). I asked him if he could jump a wire to the trunk light to activate the alarm, and he told me that that solution was not possible.(He said something about a part of the car being "positive triggered" and the other one "negative triggered". By this I mean the car doors and the trunk). The solution that he offered was installing a mercury switch in the trunk, but it cost more money.

This car had an alarm before and I remember that it had a cable that was jumped from the light to another place. Can somebody help me figure this out so I can do the modification and complete the trunk protection?

If there's a trunk light there must be some kind of switch for it if the light comes on when you open the trunk.
POS switching doesn't matter, most alarm have a spare door trigger wire for POS input or you can switch it with a relay.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Most U.S. domestic trunk lights have internal mercury switches, so they can't be tapped for the alarm trigger.

Use a stick-on magnetic reed or mercury switch. Because they have two wires, they can be wired with either polarity. I see the installer offered you that option. The "costs more money" part is for the time required to run the wire to the trunk. Which is needed for any trigger, even to use the light, if it were possible. Which it isn't.

I'm quite surprised at that we got rid of them in the early 80s, mercury content and they often failed.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

I don't know about current production, but I can think of numerous vehicles I've owned, and still own that have mercury switched hood and trunk lights. A 1999 Sunbird probably does too.

They had them as hatch switches on the 81 on European Ford Escorts, ONE screw fixing, they always failed.
Personally I prefer the Japanese use of a microswitch in the locking mechanism.
My last car had two hall effect switches in the door lock/actuators.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

There are no mercury switches on any late model vehicles. The switch is in the latch itself.

Yes Craig, Japanese fashion using a microswitch.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Black positive in polarity at the light.

I can not think of a reason they would make it positive in polarity. Use a meter to verify.

BMW 5 Series, Mercedes,880s -90s UK Ford Puma, all had POS switching trunk lights, and it's 7:15am on a Saturday morning, why would I know why.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.