TH-400 / 200-4R Torque Converter Lockup Solenoid Wiring Diagram
Schematic of a TH-400 torque converter lockup circuit showing vacuum switches, check valve and electrical switches with a numbered legend.
This is a hand-drawn schematic showing how to wire a torque converter lockup circuit for an automatic transmission (the legend references a TH-400 one-wire case connector; the file is labeled as a 200-4R wiring diagram). The diagram traces a vacuum signal from manifold vacuum through (1) a ported vacuum switch that only passes vacuum once the engine reaches operating temperature, then through (2) a vacuum check valve to (3) an electrical vacuum switch that is closed when vacuum is present and opens when vacuum drops. The electrical circuit runs from (5) a 12-volt source that is hot in the run position, through (4) a normally closed brake light switch that opens when the brake pedal is pressed, through the vacuum switch, and into the transmission via (6) a single-wire connector through the transmission housing. Inside the transmission, the wire feeds (7) the torque converter lockup solenoid, which is grounded through (8) a normally open pressure switch. A reader learns the sequence and function of each component needed for manual/automatic lockup control: lockup engages only with the engine warm, adequate vacuum present, the ignition in run, and the brake pedal released, with internal pressure-switch control completing the circuit.
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Frequently asked questions
- What components are needed to wire a torque converter lockup solenoid per this diagram?
- A ported vacuum switch, a vacuum check valve, an electrical vacuum switch, a brake light switch (normally closed), a 12v source hot in run, a one-wire connector through the trans housing, the lockup solenoid, and a normally open pressure switch.
- How does the brake pedal affect the lockup circuit?
- The brake light switch (item 4) is normally closed and opens when the brake pedal is pressed, cutting power to the lockup solenoid.
- What does the ported vacuum switch (item 1) do?
- It prevents vacuum from passing through until the engine reaches operating temperature, so lockup only functions when the engine is warm.
- How does the electrical vacuum switch (item 3) operate?
- It is closed in the presence of vacuum and opens when vacuum drops, breaking the circuit to the lockup solenoid.
- Where does the wiring enter the transmission?
- Through item 6, a TH-400 one-wire connector that passes through the trans housing, feeding the torque converter lockup solenoid (7) and pressure switch (8) inside.
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