I am trying to put a rear hatch release into a 78.
I have a release motor from an 88, and am trying to figure out how to wire it up.
I have a console switch out of a 944 that I will use.

There are three wires into the motor: red, brown, yellow.

I have checked on my 89 to get an idea of how it should work.
on m 89:
voltage checks:
Red, 12v always.
Brown is ground when the door is open.
Yellow gets 12 volts when the release **** is pulled with door open or closed.


Now the switch has three wires red, white, and blue.

Blue to white is a closed circuit until the button is pressed, then red to blue closes and blue to white is open.

So I believe this will work:
At switch:
Red to always hot.
Blue to the yellow wire on the motor.
At motor:
Red to always hot.
Brown to one of the door(interior lights) brown with white stripe. (grounded when doors are open)
Yellow to blue at switch.

I still need to figure out what size fuses to put in, and where.
I assume I will need a fuse on the red wire to the motor.
And another fuse either on the red wire to the switch, or on the yellow wire to the motor.

Any comments, suggestions, or corrections welcome!

 

Pictures of the switch:

 

Do you also have the receiver that the motor mounts to ? Also as I recall there is a relay involved in the normal circuit that responds to the motor and parks the tab in the closed postion....much as your wiper motor relay does.

 

The hatch release drive unit has three electrical connections:
Red: Power, always hot. This drives the motor to the normal rest position after the pull switch is released, thus the locking flap is retracted so that the hatch can lock in place.
Yellow: Power, applied only while the pull switch is operated. This starts the motor cycle.
Brown: Connected to the switched ground circuit operated by the door and hatch switches, so that the hatch release works only when a door is open.

When a release switch is operated and a door is open, power from the switch runs the release motor to operate the release flap. The flap must be in the rest position for the hatch to lock when it is closed, so a segmented disk inside the motor gearbox conducts power from the yellow (constant hot) wire to the motor until the flap is in the rest position, where a cutout portion of the segmented disk cuts off the power from the yellow wire, stopping the motor.

The switch that you use must be momentary-contact, normally-open, single pole. It should furnish 12 vdc to the yellow wire while operated.

The red wire should be fed constant fused power.

The brown wire should be hooked to the brown/white circuit operated by the interior light door switches. There should be such a wire on the bottom of the hatch lock receiver.

You will also need the later hatch lock receiver.

 

The 78 already has the lower receiver from the 88 (with the actuating arm). I had to modify the hole a little to get it to fit in.
I have the whole ce panel and most of the wiring harness from an 88, but I did not think the rear hatch had a relay, but could be wrong.

My 78 has the connector (yellow) in the console for the sun roof that is wired to the CE panel at fuse 8, and to a white connect behind the rear pass quarter panel. (my car has no sun roof). I am planing on using these.
On a side note it also has a unused blue connector back there. The red and green run he windows, yellow is for the sun roof, but no clue what the blue one would have been used for. (OB have the rear wiper in the pod).

 

Wally,
Thanks, I forgot the PO had cut the ground-to-switched ground wires at the lower receiver. I will repair that and connect into it.
Do I need to put a fuse on both power circuits?

 

No relay on any model year.

Alan

 

You are correct on the switch usage & motor wiring. You need a 1A (or could use a 2A or 3A) fuse for the continual power to the red motor wire and a 5A fuse for the feed to the yellow motor wire via the switch.

Stock the switch is fed from the interior lights supply so you could alternatively pick that up - otherwise you could connect both the wire to the switch and the direct to the motor from the same fuse (5A) on a dedicated always on supply (as you note).

Alan