BW35 to M46 Swap - Wiring Harness Confusion

Hi there,

I'm prepping to do a tranny swap in my 1980 240 GL and I'm running into some issues trying to figure out how to wire up the Overdrive. Apparently in 1980 cars the OD for the for M46 is on a switch rather than a button found on later models. Also, according to the wiring diagram from that year the it does not have a relay either (not even the earlier blue relay). The M46 that I bought is from a later model (the guy didn't remember by said it was around '85), so my question is how can I wire this thing up properly? Any help would be greatly appreciated.

Cheers

Do you have the push button shifter? You can build a simple latching relay to supply power to the od unit. If you have the sliding switch it's even easier, the power will go through the 4th gear switch as well so od will be disabled in any gear but 4th ( should run either activation switch through the lockout)
https://goo.gl/images/Qqwcns

I currently have no shifter, but I do have the wiring harness. I was thinking about getting the switch shifter to make it closer to stock but not sure if it will work with a newer harness that has the relay plug. This is what I wanted to make sure before I ordered a bunch of the worng parts.

I completely rewired mine. I bought the wiring harness from Dave Barton he makes them. It's perfect. It also has the right connection for behind the instrument cluster. Just use the push button and install the relay. I got my relay from fcp euro just make sure you research the right relay. They're 2 relays 1 for auto and manual. I think the blue one is what you want. that relay and wiring harness is all you need. It's easy to run the harness. took me 45 mins to wire everything up.

what shifter do you have button or switch?


good luck

The transmission I got didn't have a shift knob or button so I was thinking I'd buy a switch to have it as close to stock as possible, but if the button is the easier option then I'll probably just go with that. Do you think Dave's Harness will still work with the old style instrument cluster?

som_brio said:

if the button is the easier option then I'll probably just go with that.

Click to expand...

The relay option is not in my opinion easier. It is much more complicated to wire. For the early setup, the power comes from a fuse to the slide switch, then comes out of the switch and goes to the 4th gear lockout switch on the top cover. From there, a wire goes to the solenoid. Also, there is a branch that goes to the instrument connector.

The drawback to using the old style is that you may have a harder time getting good shift knob parts. The top cover where the switch mounts tends to degrade with age. I am not sure if they are available new.

I have attached a diagram for the relay type. I don't seem to have one for the other

I have just the top part of a slide switch knob with the switch in it that's in good shape, pm me if you're interested, you'll still need the bottom half of the knob though.

I have a genuine Volvo NOS M46 early harness for $55 shipped.

You're gonna need a different 4th gear switch if you plan to use the slide switch with no relay. It needs to be a flow through type instead of making contact to ground. You can't use a switch from an early trans because it goes into the rear housing and not the top cover so the threads are different, not to mention it's NLA. I think a reverse light switch will work, but you'll need to modify the harness to use it.

https://www.ipdusa.com/products/7213/113201-reverse-back-up-light-switch

Thanks for all the info guys I really appreciate it! I'll let you know how it goes when I get around to putting it all in the car. I think I'm going to go for the switch system