02 Ram Diesel Manual Trans Remote Start

I installed an Ultra Start Remote / Auto Start and everything worked for awhile but after several months would no longer go into 'reservation' mode. I am able to start to get it into reservation mode . . . . it will run without the key but it won's shut down. . .   The brain does not seem to see the door open (or close). The Ultra Start System has an input for positive and negative when door opened (as shown in picture of manual). I had the door trigger connected to the negative (green wire) input and it was working originally and I did not change anything. The vehicle diagrams show a tan wire at the door pin with a negative output. Now that it is not working I took the multimeter to it and it is reading .05 (+) volts when door opened (lights on) and 4.4 (+) volts when the door is closed (lights off). Why would it have worked originally? I tried connecting to the positive input (purple wire) with no success. Interesting, both the negative input (green wire) and the positive input (purple wire) from the Ultra Start computer show 3.4 + volts without being connected to anything. Any thoughts?

I suspect that the 5V logic-level on the truck's tan door switch wire is not high enough for the Ultra to detect the door has closed. You need to drive the door switch input on the Ultra to 12 V. You must have been right on the threshold of it working, and it did for awhile, but now it doesn't. I can see this. 5V is close to what the module logic level is (3.4V). You need 2 diodes and a 10.000 Ohm resistor. !/4 watt is fine. Cut the tan door switch wire in two. Connect the band end of both diodes to the switch side wire. Connect the non-band end of one diode to the truck side tan wire. Connect the non-band end of the other diode to the Ultra (+) door input AND one end of the resistor. Connect the other end of the resistor to constant +12 Volt. This mod will drive the door input to 12V when door closed, but the BCM will only see the 5V it does now. Should work.

Thank you. . . . I'll give that a try. The thing I am still confused about is why the readings from the tan line are positive and the diagram shows they should be negative and why it originally worked when connected to the negative input on the Ultra Start.

The tan wire is connected to the BCM. BCM's and ECM's use "Logic High = Yes = High = Binary one". "Logic Low = No =Low = Binary zero". An input is at module voltage (usually ~5VDC) when high, and if shunted to ground, it becomes 0-Volts. So when the door is closed, the tan wire is not shunted to ground, the level is 5 Volt which is a Logic High = "Door is closed". When the door is open, the tan wire IS shunted to ground, the level is 0 Volt which is Logic Low = "Door is open". Hope that makes sense. The work-around I suggested above with the resistor is basically the same thing, but for the Ultra, and the voltage is 12.

CORRECTION: Use the Ultra's (-) NEGATIVE door input. Repeat, (-) Negative. In my post I said (+). This is wrong. Sorry for the confusion. Use Negative door input.