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Old 11-07-2019, 04:38 PM   #1
krisebra
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Default replace m47 with m46

Hello! im new on the forums, and i tried searching for it, but i am currently working on swapping the engine and gearbox in my 92' 940 from B230FB with m47 to B230ET with m46.
i got everything i need to do the swap, but i wonder how much of a hassle it is to hook up the overdrive on the m46? Do i need to wire up the whole circuit or do i just need to pop in the relay and hook up the gearbox?
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Old 11-07-2019, 11:06 PM   #2
dl242gt
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It's easy to connect up the overdrive. You can buy wiring harnesses from suppliers like Dave Barton to wire up the whole thing. It's nice because you are using all new wire. The overdrive relay and wiring can be setup like it's in a 240. You'll just have to wire in a fuse and connect it to switched power.
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Old 11-08-2019, 04:55 PM   #3
John242Ti
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You can also use the 1975-80 overdrive wiring. You'll need the early shift knob and pattern cap with the slider switch, the early 4th gear switch that threads into the top of the transmission, and the wiring harnesses. The blue wire connects to fuse 11. Yellow wire can be attached where the upshift light is connected (terminal next to the bulb at the bottom of the cluster), then the rest of the wiring goes down to the passenger side of the center dash console. The shift lever harness plugs into the two terminal plug. The red wire from the transmission harness plugs into one of the spots on the two terminal plug. On the transmission, the red wire goes to the 4th gear switch, and the yellow wire on that harness goes to the solenoid. There's a diode attached to it that goes to the other terminal of the solenoid, which has a piggyback terminal for the ground wire. Its purpose is to limit the amount of current that backflows through the harness when you disengage the overdrive.

Anyway, it's a little easier to wire up and doesn't require a relay. The only thing you have to remember is that it will not automatically turn off the overdrive circuit when downshifting, so it will drop into overdrive as soon as you engage 4th, if you forget to flip the switch to "out" from "in".

-J
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1982 242Ti - black, M46. 1985 245Ti - blue, M46. Formerly Blue245Ti, 245GT-Turbo, and, originally 242GT-Ti.
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