heat senders
- Thread starter 42ford
- Start date
Old Henry
Well-known member
The one with two posts is just an one-off switch. It's on below 212° and off above that to break the circuit to the other one and send the gauge to maximum hot. It can be tested by checking continuity through various temperatures, i.e. clamp your ohm meter to each post, immerse it in water, and heat the water with a thermometer in it to see if the switch opens at about 212°. Whatever temperature that switch opens at is the temperature that the gauge will go to maximum hot.
The other, single post, sender is a little more tricky. It is a variable switch that varies the current passing through the gauge into ground at the sender at various temperatures. An ohm meter would not really test it because it's not actually variable resistance, the switch actually oscillates off and on at various rates depending on the temperatures to control the current that goes through the heater in the gauge that deflects the needle. When in doubt about it I have just replaced it. I have also installed a mechanical gauge hidden in my glove box that measures the left head temperature so that I know more accurately the temperature. See here: http://www.fordbarn.com/forum/showthread.php?t=88541
Here's a diagram of the system to better understand how it works:
Close up diagram:
The other, single post, sender is a little more tricky. It is a variable switch that varies the current passing through the gauge into ground at the sender at various temperatures. An ohm meter would not really test it because it's not actually variable resistance, the switch actually oscillates off and on at various rates depending on the temperatures to control the current that goes through the heater in the gauge that deflects the needle. When in doubt about it I have just replaced it. I have also installed a mechanical gauge hidden in my glove box that measures the left head temperature so that I know more accurately the temperature. See here: http://www.fordbarn.com/forum/showthread.php?t=88541
Here's a diagram of the system to better understand how it works:
Close up diagram:
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