1970 Transmission Controlled Spark (TCS) Switch
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Pro
Joined: Mar 2003
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From: Texas
1970 Transmission Controlled Spark (TCS) Switch
What is the part number for the 1970 Transmission Controlled Spark (TCS) Switch located on the passenger side head
UPDATE: GM # 3961573, Its a two terminal temp sensor, with the same dark green wire connected to both terminals
UPDATE: GM # 3961573, Its a two terminal temp sensor, with the same dark green wire connected to both terminals
Last edited by split63; Nov 21, 2025 at 01:09 PM.
Le Mans Master
Joined: Apr 2001
Posts: 5,941
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From: Was New Orleans but swam to Baton Rouge LA
Cruise-In IX Veteran
This is what you are talking about. https://www.lectriclimited.com/trans...-switch-106278
This switch controls the temperature range that will operate the solenoid allowing vacuum advance to the distributor. It also has a switch to ensure the car is in 4th gear for this to activate.
Safety Car
Joined: Dec 1999
Posts: 3,606
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From: PA
TCS is an electric/vacuum system… There are actually two switches; a temperature switch in the head (which is what you are looking for) and an electricity driven (contact) switch in the transmission. This is all tied into a solenoid that that controls distributor vacuum depending upon temperature and transmission gear position. For 1970, the TCS system limits full advance until 3rd and 4th gear, for 1971-1972, full advance is limited to 4th gear.
Regards,
Stan Falenski
Regards,
Stan Falenski
Melting Slicks
Joined: May 2002
Posts: 2,476
Likes: 756
From: Laporte, IN
TCS is an electric/vacuum system… There are actually two switches; a temperature switch in the head (which is what you are looking for) and an electricity driven (contact) switch in the transmission. This is all tied into a solenoid that that controls distributor vacuum depending upon temperature and transmission gear position. For 1970, the TCS system limits full advance until 3rd and 4th gear, for 1971-1972, full advance is limited to 4th gear.
Regards,
Stan Falenski
Regards,
Stan Falenski
Stan
72 was the year the TCS was 4th gear only. CEC for 71 3 and 4th would get Vacuum.
