Wiring harness!!

It’s a two piece deal. On the right is the section that connects to the fan control switch. The other end of it is a four pronged dongle. In the middle are two grounds (to go to the steering wheel mount), one black(pink/green) wire (that will go to the #12 terminal of the fuse box) and one white/blue wire that gets connected to the 16(?) prong connector that to the back of the gauge cluster (wired to the #12 prong). I think this goes to the dimmer(?)

The wiring harness on the left connects to the fan, the receiver for the four prong dongle thingie, the resistor pack for the fan and a single black(red/green) wire that goes to the A/C thermoswitch (Make a note of this for later).




The old fan connector on the 240D were blade type connectors. The connector for the 300CDs fan is a standard familiar keyed male connector. I rewired it to accept the female half for that connector.




The lights and connectors for the dials were actually on two separate wiring harnesses in the 240D and not on the blower fan wiring harness. I cut them off and then rewired them into a new single wiring harness with an extra connector from the speakers so they would be disconnected separately.




I had converted the 300CD to a manual 4-speed transmission from another 240D. The auto transmission had a light that lit the selector gate for the auto shifter. Since there was no place for this with the manual shifter, the light went unused. I now needed a power source for the mini lighting harness and this is where I tapped into for power.





These are the harnesses for the blower fan resistors. Theres a bit of difference between the two as you can see. The 300CD is a 4 or 5-speed fan (maybe, I never got the thing to work so who knows) with a 6-pin connector. The 240D is a 4-pin connector and is a 3-speed fan system. The 240Ds harness also has the plug go directly to the fan whereas the 300CD the plug is on the main harness of the servo system. The 240D also has one half of the connectors for the A/C receiver-drier (ill get to this in a bit). I simply swapped over the 240Ds wiring harness. I could have done a bit of resistance testing and rewire things, but it was easier to pull the heater/evap box a bit forward to swap the harnesses.




The center vent was kind of a head scratcher.

The center vent in the 240D is located further back on the top of the heater/evap box than the 300CD. Its also actuated by a slide lever and bellcrank system that converts left/right motion to in/out and then finally up/down to open the center vent like a trap door. It’s a pretty clever setup. The 300CDs vent is (as mentioned) closer to the front and is actuated by a vacuum pod (in/out motion opens trap door up/down).

Because of the difference in location. The linkages wouldnt work as everthing was on top of each other. I couldnt swap the vent doors either as they are specific to their respective boxes. Another solution had to be found.

What I came up with was the setup you see above. I pulled the vacuum pod and kept the actuator rod. Then I straightened the manual slide lever actuator rod(had a 40-ish deg bend in it), cut off the clevis at the end and bent the last ¾” 90deg. I cut a new hole for the new revised actuator rod and clearanced the vent flap a bit for it. Finally I cut a small hole in the vents rubber boot so the new actuator rod could pass back and forth through it. After a bit of trial and error with cutting the hole in the rubber boot (I didn’t want to make too big of a hole, just big enough) everything works as intended.




And there it is. Everything is in and the heat works perfectly. I can send heat this way or that way, its awesome! This is lightyears better than the servo driven system.

Is everything perfection though?….No, not everything works.

The two vacuum servos (top of the blower fan and back of the heater box for the rear vents) aren’t working right now. Not surprising as the doorlocks have been wonky for a bit. Before I dreaded the prospect of tracing down leaks in the vacuum system. Now with the rats nest of vacuum lines/dealios gone, things are massively simplified. I feel much more confident in tackling this minor detail now.

Air conditioning….no workie.

I had alluded to this. The system has been without charge for years and the girlfriend doesn’t seem to care much (she used to drive to the central valley of California in the summer like this), so I hadnt really made an effort to get the A/C system functional.

I don’t think there too much to do though. The 300CD has one plug for the receiver-drier and both plugs for the thermoswitch on the main servo harness. The 240D has both plugs for the receiver-drier on a separate harness and one plug for the A/C thermoswitch on the blower harness. The end result when you swap the harnesses is that the conversion leaves one connector on the receiver-drier blank and one connector on the A/C thermoswitch blank. I think this would be pretty easy to figure out what needs to be done there.

In the end, Im pleased with the results. Its already um..eleventybillion times better than the old system(for one it actually blows heat). Was this a silly way of doing this conversion? Yes. I could claim ignorance but I did see Bruce Kennedys suggestion so…yeah. Sometimes we aren’t as good as we can be. It was an error, but hopefully my mistake can be useful to others in the future.

Hopefully this is somewhat clear and I didnt miss anything big.

Cliff notes: swap the boxes.

Gavin