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Junior Charter Member
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Discussion Starter · #1 ·
I'm in the process of wiring the dash and am having some problems with oil pressure and water temp gauges. I'm using the FFR electric classic gauges with the supplied sending units.

First with the water temp. From the gauge, there are 2 wires that go to the sending unit. When Ii heat the sender, the resistance across the wires drops, not to a dead short but low enough that at one point it could trip the fan relay and start the fan. At this point there was no reading on the gauge. If I remove the fan wiring (ground lead to the relay to the high side of the sender - the other lead goes to ground through the gauge), I get a temp reading but no fan. I should note that the engine is not in the car and the gauge is not grounded. But...I can find no connection through the sender (hot or cold) to the case, so the sender does not seem to ground to the engine/chassis. Can I run the relay in series with the sender? I have so far only tried parallel, not wanting to run any exessive current through the gauge.

Suggestions???

Now for the oil pressure. Under pressure (compressed air at this point) the resistance drops. I would like to run a no pressure light but at this point, I can only see the light coming on when the resistance drops which happens when I have pressure.

Any suggestions other than connecting another sender??

The instructions from FFR do not provide much info and the wiring diagram I have shows a single wire to either sender with the housing being grounded to the block.

Here's another. I'm using an SPDT switch for the headlights. Park lights on one side, headlights on the other. Can I run a diode from the headlight wire across the switch to the park light wire (in the correct direction) so the park lights still operate when the headlights are activated.

Thanks guys, I know the answer is out there but after spending the last 3 days on wiring, my head is FRIED!

Peter
 

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Premium Member
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1,947 Posts
The gauges should have seperate senders for them. DO NOT wire the temp gauge to the same sender that controls your fan.

Temp sender works off of liquid temp to increase resistence to ground as it get hotter.
Fan sender completes ground when the switch get to a certain temp.(some are single wire and some have two leads, one goes to ground other goes to fan)

Oil pressure warning light should have a seperate sender that will complete ground if pressure drops below a certain PSI. I believe Jegs or Summit have a kit for this.

As for the headlights I used a completely different system (ISIS) do I cannot help you with that one.
I' sure other will chime in.
 

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Junior Charter Member
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333 Posts
Discussion Starter · #3 ·
TTT

This is a carbed 302 with limited spots to install additional sensors.
 
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