Blower motor switch modification

[B1Toad]

Here is a simple mod which I think will eliminate the small terminals overheating on the mode switch and melting stuff, the first terminal fails because it carries the most current as it also supplies the current for the other controls. (mine melted the yellow vacuum hose as well).

The original circuit path (in yellow) brings the ground from ground point #202 in the footwell to the first terminal on the mode switch. It then passes thru the the mode switch so it can shut the fan off when there is no mode selected as the fan switch is only a speed control and has no off position. So all this current comes in on the black wire, goes thru the mode switch, comes back out on the dark green wire when a mode is selected (all on C3) then the dark green enters the blower switch (thru C1). Here is my plan, new circuit path in blue dashes:

1. Cut the dark green wire between the mode switch and the blower switch and connect the part from the mode switch to #85 of a relay.
2. Connect the other half to #87 of the relay.
3. Connect #86 on the relay to an ignition switched circuit.
4. Connect relay terminal #30 to ground by either tapping into the black ground wire before it enters the mode switch, or run a new ground wire (at least #12).

Now when you start the engine with the mode switch off, the relay coil gets battery power but doesn't close because it is not grounded. When you switch the mode switch to any mode, the green wire grounds the relay which then closes and completes the new ground circuit to the blower switch, directly to the blower switch without passing thru the mode switch. The mode switch will now only see a tiny bit of current since the blower current is now bypassing it and the switch and connections will likely last forever.


What do you think?

 

[B1Toad]

Got er done today, easy mod. I used the cig lighter power for the relay per Mac's suggestion and it made things real easy. I also ran a new #10 from the ground point in the footwell and attached it directly to pin #30 on the relay, which gives me a good source for the blower motor plus eliminates the need to splice 3 wires together at the control. A #12 would work too but it so happens that I have a ton of #10 and hardly any #12.

I spliced a #14 onto the original #12 ground which made it fit a .187 spade connector plus made a section of more flexible wire so the stiff #12 is not pushing and bending on that tiny spade connector on the switch. I used the gold plated .187 connectors because the tin ones are extremely weak, the gold ones are tough and fit tight (I did have to cut off the insulator and use heat shrink instead to fit it next to the adjacent terminal). I kept the other two connectors on the original 3 pin plug by simply slicing off the bad one with a multi-tool and the remaining section still latches securely onto the back of the switch.

When finished I re-taped the harness as best I could and wrapped the relay in a layer of foam to prevent another rattle and tucked it in behind and to the left under the radio where there is a nice little pocket there. I've started labeling my electrical mods because down the road I'll have no clue how I did them.

Everything works as it should and now there is no more heavy current going thru my dash controls. This mod also allows you to keep your old controls if the ground terminal is salvageable since you can clean it up and it will hold up because it will now only see a tiny bit of current and it won't heat up again.