Reverse switch on th400 transmission

selinoid ? Solenoid Wouldn't think so , but you never know without testing . With the truck running you step on the brake which let's you shift from park into a gear . That part works right ?
Automatic Transmission Shift Lock Control Circuit Description
The automatic transmission shift lock control system prevents the automatic transmission from being shifted out of park position unless you depress the brake pedal with the ignition in run or start. When the ignition switch is in run or start, the current flows from the BU/LPS fuse located in the engine wiring harness junction block through CKT 839 (PNK) to the park/neutral position switch. The park/neutral position switch also feeds the backup lamps portion of the switch. With the transmission in park, the current flows to the automatic transmission shift lock control fuse located in the engine wiring harness junction block through CKT 275 (LT GRN). The current then flows to the stoplamp switch through CKT 584 (LT GRN/BLK). The current continues to the automatic transmission shift lock control solenoid through CKT 1135 (DK GRN/WHT). The ground path is provided through CKT 1850 (BLK) to G203. When you depress the brake pedal, the normally closed contacts in the stoplamp switch open and the current flow is interrupted. When the current flow interrupts the automatic transmission shift lock control solenoid de-energizes. The transmission may then shift to another gear. Once the transmission shifts to another gear (except park), the contacts in the park/neutral switch are open thus stopping the current flow to energize the solenoid when the brake pedal releases.

Should test your transmissions front pump for pressure take the two transmission lines off the radiator and run them into a 5 gallon bucket and start it and look in the bucket and see if you have pressure coming out one of the lines if no pressure or weak pressure front pump is done look for a replacement most older transmission can have reverse and no forward gear due to lack of pressure or low fluid level.

Possible reverse light switch. Or park/neutral safety switch. What side of the case are the wires coming from?

on the side of the box there will be a switch with 2 terminals. ( round object screwed in. It may also be in the back id the box as it is activated by the selector rail that works reverse gear. place in reverse , turn on the ignition and have someone check for lights as you touch the wires to the terminals of the switch. There will be a switch likewise for the transfer case section for the 4x4 light . repeat the operation with the wires to see if the light comes on

You will have to have an adapter plate made, you will need an adapter for the bell housing to the block and the same thickness plate to adapt the flywheel to the torque converter.

Hi Joe,
I found this information from Vince in another site, I hope helps you to find the problem. This information is for a 1997 Dodge Caravan, should be very similar to your 2003 minivan.
The back up light switch is on the side of the transmission by the transmission fluid cooler lines.
REMOVAL
Unscrew switch from transaxle case allowing fluid to drain into a container. Move selector lever to PARK, then to NEUTRAL position, and inspect to see the switch operating lever fingers are centered in switch opening.

INSTALLATION:

1. Screw the switch with a new seal into transaxle case and tighten to 24 foot lbs. Retest switch with the test lamp.
2. Add fluid to transaxle to bring up to proper level.
3. The back-up lamp switch circuit is through the two outside terminals of the three terminal switch.
4. To test switch, remove wiring connector from switch and test for continuity between the two outside pins.
5. Continuity should exist only with transaxle in REVERSE position.
6. No continuity should exist from either pin to the case.

I hope this helps. Good look!

I

You'll have to go to GM for this diagram, but sounds like it's just dirt plugged the movement of fluid to reverse clutch pack. Since Google is your friend, type in "fluid path diagram for a GM TH400 transmission" and see what comes up.

is it a electronic transmission, or manual! this makes the difference! call a ****** shop to get more info on this. good-day!

a np241 from a th400/4l80e would have the 32 spline that is need for a manual trans, one from a 700r4/4l60e is 27 spline input, in 94 the switch was changed and the cam to activate the switch was changed so if you get a 94 np241 you then will need to wire in a 94 switch into the older harness

not a plug , though kinda looks like one , but a neutral safety switch at the transmission (follow the wire to side of trans case)