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Transistors have two polarities: N-type and P-Type. In this application you would choose an P-Type.
A FET has three pins: The Drain, the Gate, and the Source. If you look at the little package a FET comes or its data sheet the three are identified as D, G, and S.
You would cut the wire which supplies power from the rear battery to the ABC controller. The feed from the battery would then go to the Source pin, and the Drain pin would go to wire going to the ABC power. There is a wire which supplies switched power to the ABC controller, and you would tap that and wire it to the FET's Gate pin. I could mail you a little "tap" which works by clamping onto a wire.
I don't know if you followed that, but even if you didn't I think you can see it is fairly simple. If you go this route I'm going to draw a schematic with my CAD software.
I was able to follow you. Do you know which wires they are? I have taps here, but i looked at FETs online and they seem like the pins are super close. May be hard to handle or build under the dash. Is there a FET that you know of that is more separated?
You can get a high-powered FET where two leads are about 1/2" apart and its metal case is the 3rd terminal. The ones that I have in mind have pins/leads that are closely spaced, but you can bend them to spread them wide apart.
The attachment shows the power wire from the battery on socket #48 of the large ABC connector and the switched power wire on socket #46.
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I went to mouser.com and through the process of elimination ended up with just one candidate. I've uploaded its spreadsheet. Probably going to need to wire a resistor between the Gate and Source of the FET.
I went to school for hardware design but made a career in programming. So I want to run this by a friend who knows hardware and see if he has a recommendation.
I went to school for hardware design but made a career in programming. So I want to run this by a friend who knows hardware and see if he has a recommendation.
The friend would use a relay. But a relay is harder to wire: The pins are much shorter than the FET and spaced close together. I'd go with the FET. And I would put a 10k-ohm resistor between the Gate and the Source.
I mildly enjoy drawing simple schematics in CAD, so if you would like one just ask!
Here is a drawing. You can use a relay, and its contacts would go to where you see the FET's Drain and Source connected. The relay coil would wire to socket 46 and chassis ground.
I have a transmission controller for Mercedes' old 4-speed automatics (picture). You can see it has a connector which enables you to unplug it from the car. In your case you could have a 2nd female plug with no FET and no resistor but has a jumper installed so that you could restore ABC to factory original.
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Here is a drawing. You can use a relay, and its contacts would go to where you see the FET's Drain and Source connected. The relay coil would wire to socket 46 and chassis ground.
I have a transmission controller for Mercedes' old 4-speed automatics (picture). You can see it has a connector which enables you to unplug it from the car. In your case you could have a 2nd female plug with no FET and no resistor but has a jumper installed so that you could restore ABC to factory original.
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07-04-2020, 11:17 AM
