1972 Electra - HOT and STOP warning light in dash

Discussion in 'Sparky's corner' started by colonel, Jul 12, 2023.

  1. colonel

    colonel Speedjunky

    I ran to the local Home Depot yesterday. It was like 85° F outside, so: hot , but not thaaat hot.

    When I came out and started the engine, the HOT lamp in the dash came on. I checked under the hood, radiator hot, both tubes hot, all belts there, fan works, water in the reservoir. OK. Let the car sit for an hour in the shade, cranked the engine, still HOT. Hmm. Turned on the heater, hot air from the vents, heater hoses hot under the hood, HOT light stays on. Hmmm.

    The manual says, HOT means "exessive temperature". If the engine was like REALY hot, a flashing STOP light would come on. So I limped the 3 mls home to my house at revs slightly above idle and parked the car in the shade. An hour later, the HOT light was out. The STOP light never came on.

    Can anybody give a hint how to test the flashing STOP light? The Fisher body manual doesn´t seem to cover this.
  2. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    I believe its a fairly simple circuit. If you ground the green wire the light turns on. The sensor is nothing more than a thermostatic switch that throws at a certain temp. I think its supposed to kick on a 245°.
  3. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Get yourself a temperature gauge, and/or one of those infrared temperature guns and see what the actual temperatures are. The stop engine sensor that screws into the back of the head measures actual metal temperature, not coolant temperature.
    TrunkMonkey, Eric, 1973gs and 2 others like this.
  4. colonel

    colonel Speedjunky

    Had the same thing happening again today. Didn´t have the time to initiate any diagnostics or repairs since first post.

    Checked temps with a IR temp gun today, were between 140° and 180° F in the radiator, rad hoses, intake and head where the plugs screw in. So I´d say: temp switch or maybe wiring.

    Now, where is the coolant temp switch located, is this the one ("1") to the front of the intake with the "thing" ("2" - pressure actuator?) on top? If so, where to find? RA carries "1 blade" and "2 blade" ones for light or "1 button" for temp gauge. I only have the light.

    (How) does the thing come off and what does it do? Is "4" a hose connector? I found "4a" unconnected and it fits on "4".

    "3" is the oil pressure sender?

  5. DaWildcat

    DaWildcat Platinum Level Contributor

    The only help I can offer is that the oil pressure sender is not on top of the intake manifold, rather it's low on the right side of the block near the oil filter.

    TrunkMonkey likes this.
  6. Brad Conley

    Brad Conley Super Moderator Staff Member

    3 is the temperature sender...turns on the idiot light at 245 degrees. It may have failed so secure a new sender and see if that is your problem. Is the thermostat functioning properly? good to test it too. These are all inexpensive parts so you won't break the bank in replacing them.
    Max Damage likes this.
  7. TrunkMonkey

    TrunkMonkey Well-Known Member

    3 is the temp light sender/wire (that wire is dark green).
    Max Damage likes this.
  8. colonel

    colonel Speedjunky

    So I´ll replace "3" with a 1 blade new sender. Indeed, the wire is DK GRN:



    Can anybody comment on 1 and 2?
  9. Max Damage

    Max Damage I'm thinking about it!

    Make sure the light goes off with the sender disconnected and the connector isolated from ground. If the wire is grounded somewhere else, the light would stay on.
  10. Brad Conley

    Brad Conley Super Moderator Staff Member

    1 & 2 are part of the pollution control system. It keeps the distributor from giving full vacuum advance until the automatic transmission is in 3rd gear. At this point, just make sure there are no vacuum leaks there. We can deal with it later.
  11. GSX 554

    GSX 554 Gold Level Contributor

    The " STOP ENGINE " light that flashes only senses METAL temperature at the back of the head as Larry stated . Hot light comes on first then if it continues to get hotter the STOP ENGINE light will flash . I believe that is at 260-265 Degrees . . The test of it is when the key is in the CRANK position it will light .
  12. colonel

    colonel Speedjunky

    Both lights go on when cranking the engine.

    Drove the car 20 mls each way to the a/c shop. No lights - strange. What did I do? I tightend the gas line fitting to the carb (fuel dripping out) and put the 4a hose on the 4 port of the pollution control system. Can´t belive any of those affects the HOT light.

    Ordered a new sensor anyways and will revert once installed.

    Oh - Ice cold air now :)
    Last edited: Sep 9, 2023
  13. Eric

    Eric Founders Club Member

    You can't just throw parts at it. Shop Manual is most helpful if you have patience and research the systems functions. And in my honest opinion...listen to Larry the Wizard.
    He has helped me throughout the years in getting my Buicks to run properly the correct way.
    Last edited: Sep 15, 2023
    timesublime and TrunkMonkey like this.
  14. TrunkMonkey

    TrunkMonkey Well-Known Member

    Almost everything in a "negative ground" car's system is basically, power is "supplied", but until the "switch" (whatever accessory) is "grounded" there is no completion of circuit.

    In other words, the cigarette lighter does nothing, until you push it in and "ground it" completing the circuit, and the element gets hot and "pushes" the lighter back, breaking the circuit.

    The brake light has a power wire that is not energized until you press the brake pedal, and create a "grounded" (complete) circuit and the brake lights then illuminate.
    Same for everything else. Until the switch or other component completes the circuit by "grounding", nothing happens.

    In the Buicks that had a "HOT" and "COLD" light there was either two switches, or a combination switch.

    The firs had a "COLD" switch that was "grounded" (completing the circuit and causing the light to illuminate) until the car reached the minimum warm temp to extinguish the light, and the typical "HOT" temp light that the sensor was normally open until the temp reached the point to close, completing the circuit and showing the coolant temp was "HOT", somewhere about 245f-265F.

    The "COLD" light was illuminated after start when the engine was "cold" and went out when about the time the thermostat would open, so the car was warm enough to drive, provide heat and defrosting. (one of the elegant, comfort and reassuring things luxury cars were noted for).

    Most (idiot lights) were first "triggered" with key "ON" or in "RUN" during cranking, then, extinguished when the ignition switch was in the "RUN" position. That was a circuit in the ignition switch to provide direct feedback during start to let folks know the circuits were working, and to give positive confidence that if a condition occurred with regard to any of those systems, that a warning would be provided.

    If you can't sort things out, PM me. I will help where I can.

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