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Thread: MFI temp switch start and temp switch assist

  1. #1
    Senior Member Chris Pomares's Avatar
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    MFI temp switch start and temp switch assist

    One is -10C to 140C the other is +10C to 140C.
    What wire goes to each post? One has 2 yellow wires and one has one yellow wire.
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    Last edited by Chris Pomares; 06-20-2019 at 04:51 PM.
    1959 Auratium Green 356A Super w/ Rudge wheels
    1970 Irish Green 914-6 w/2.2S
    Current -1967 Bahama Yellow 912 POLO 2cam4 #1
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    Personalized Vintage Porsche's and parts
    I couldn't find the sports car of my dreams, so I built it myself-Ferdinand Porsche

  2. #2
    member #1515
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    What year car? I've only got one on mine.
    David

    '73 S Targa #0830 2.7 MFI rebuilt to RS specs

  3. #3
    Senior Member Chris Pomares's Avatar
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    Henry of Supertech built this 2.4 with mod S cams.
    1959 Auratium Green 356A Super w/ Rudge wheels
    1970 Irish Green 914-6 w/2.2S
    Current -1967 Bahama Yellow 912 POLO 2cam4 #1
    www.reSeeWorks.com
    Personalized Vintage Porsche's and parts
    I couldn't find the sports car of my dreams, so I built it myself-Ferdinand Porsche

  4. #4
    You can't do it wrong, the connectors are different sizes,,,,but the yellow goes to G.
    Early S Registry member #90
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    Fort Worth Tx.

  5. #5
    Member #226 R Gruppe Life Member #147
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    I would ditch the -10* thermo time switches and use the 45* ones. I would also only activate one of the switches, for the cold start solenoid on the injection pump, the upper one. Disable the P circuit in the air filter housing. G

  6. #6
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    I think I would follow gled49's advice , but originally the -10 C is for the solenoid on the injection pump and the +10 C is for the cold start injection or the solenoid on the fuel filter console . You have to determine what relays the red wires go to to pick the correct time delay switch .

  7. #7
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    I took the whole -10* raw fuel prime solenoid off and used a Mercedes transmission plug to seal its spot at the Fuel Console. The raw fuel primer solenoid (top of fuel console) is a fire hazard whether connected or not. It is not necessary unless you use the car in freezing temperatures. If you do, you'll need to inspect very carefully the hoses and squirters- It is a fire hazard that was upgraded in later years into the stacks where it is a little less apt to cause an engine fire...

    Mine is stored away with other obsolete parts that came with the car.

    When I hooked up new my MFI harness I found the ThermoTime switch most forward to the driver was the one used to the rack enrichment solenoid on the 1969 MFI.


    The wire "red with no tracer" actuates the rack solenoid to full rich upon cranking. I found straight spade connectors far easier to install on the Thermo Time Switch and not short to ground when installing the boot.

    If you took the harness apart you would see the yellow wire has a jumper and that is the yellow wire in the second boot. That pair of yellow wires and ground activate the heater inside the switches- The heating acts as a timer for extra fuel on cold start. If the engine is a little warm the switch is supposed to prevent flooding.

    I hooked up the rear Thermo Time Switch that goes to the raw gas prime solenoid- but I taped off its spade connector since that solenoid is removed and plugged on my car.
    That way there is no chance of a short-
    Last edited by G69; 07-01-2019 at 12:46 PM.

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