Topic: Temp sending units


bgd8953    -- 04-15-2026 @ 11:53 AM
  Hi, I have a 47 ford flat head AB Block with 2 temp sending units, 1 on each head,. The car was converted to 12 volt, it has an auxiliary temp gauge, and only the left side is connected to the gauge, the other is not connected to the gauge. What's the best way forward, any recommendations? Thanks, Don


nelsb01    -- 04-15-2026 @ 4:39 PM
  The first question is...... with your 12-volt system can the individual sending units be connected to each other?

Originally as a 6-volt system, the two were connected, and then the sending unit with the two tabs on it was connected to the temperature gauge in the dash.

I'm a 6-volt guy and am not sure how they should be connected in a 12-volt setup, but I am sure someone who knows will be able to answer.




51504bat    -- 04-15-2026 @ 5:34 PM
  Option one: add a second gauge each with it's own sender.
Option two: an on-off-on 3 position toggle switch to allow you to switch between senders using one gauge.


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bgd8953    -- 04-15-2026 @ 6:42 PM
  I don't believe they can be connected together, it would make life simple though.


bgd8953    -- 04-15-2026 @ 6:43 PM
  Good options, thanks



51504bat    -- 04-15-2026 @ 7:03 PM
  Wiring Schematic

Left Sender (Driver): Wire to Position 1 on the 3-position switch.
Right Sender (Passenger): Wire to Position 3 (other outer position) on the switch.
Center Switch Terminal: Wire to the Gauge "S" (Signal) post.
Gauge "I" (Ignition) Post: Connect to a switched 12V or 6V source (depending on system voltage).
Gauge Ground: Ensure the gauge case is grounded.
Switch Operation: Position 1 = Left Temp, Center = OFF, Position 3 = Right Temp.

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bgd8953    -- 04-16-2026 @ 2:55 AM
  Thanks, much appreciated


JayChicago    -- 04-16-2026 @ 8:36 AM
  From original post: "...12 volt, it has an auxiliary temp gauge, and only the left side is connected to the gauge"

I take that to mean a modern aftermarket gauge. If so, it has its own sender which works on a different principal and cannot be made to work with the original sender.

However, the rest of the original gauge cluster probably has a 12-to-6 volt feed, so the original gauge should be able to work. Need to use an original sender on the right bank.


jamesmundstock    -- 04-16-2026 @ 9:47 AM
  I also have a ‘47 with the 59 AB with 12 volt negative ground. The two sending units connect together then one wire from the drivers sending unit to the factory in-dash gauge. You need voltage reducer at the gauge connection. Mine works perfect and is accurate.


carcrazy    -- 04-16-2026 @ 1:38 PM
  If you want to use your original electrical temperature gauge to monitor the coolant temperature in both heads with a 12V system, you can obtain the proper parts to make that happen with these components.

Dennis Carpenter has the temperature sending units - Right Hand #8A-10884 & Left Hand #8A-10990

Fifth Avenue has the Runtz Transistorized Voltage Reducer #95415G

https://fifthaveinternetgarage.com/electrical_parts.php


bgd8953    -- 04-17-2026 @ 3:21 PM
  Thanks


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