warning light question

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warning light question

Postby vegadude » Thu Sep 19, 2013 8:14 pm

can some one tell me why there is a hot on both sides of the bulb ? this goes for alt,oil and temp
at the bulkead conector the wires from sending units and alt split and go to each bulb witch has a pink on the otherside witch i asume is switched 12v
and the other wires go to fuse panel withc again i would asume is also 12v this is on a 71 vega
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Re: warning light question

Postby cjbiagi » Thu Sep 19, 2013 9:16 pm

You will read 12volts on each side of the bulb until you get a switched ground signal. If you have no ground at the component you will simply read the voltage through the component on each side. I assume you are measuring from each side to ground, correct? Are your bulbs not working?
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Re: warning light question

Postby spencerforhire » Fri Sep 20, 2013 5:53 am

Clyde is correct; the temp and oil senders provide a ground to light the bulbs, and the alternator works a little different but has the same outcome. The alternator is actually turned on by the voltage on the wire coming through the filament of the bulb. Blown or missing bulb= no charge. With key on, engine not running, the bulb lights because it sees ground from the regulator. When the alternator is charging, there's 12 volts on both sides of the bulb so it turns off.
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Note- the very act of listing all of these has made me realize I have some kind of problem.....

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Re: warning light question

Postby vegadude » Fri Sep 20, 2013 10:41 am

i understand that the sender provides the groundd to complete the the circuit so why would there be a third wire wire from ing switch and or fuse box
connected to the ground (sender) side of the circuit ?
i would think it be like this sender to bulb to switched 12v simple serise circuit
not sender to ing switch and bulb to ing switch
why are they also suppliing 12v on the sender side of cicuit
i have never connected a battery to this car its been an 8year restore so i dondt know what works and what doesnt and just dont
want to let out the magic smoke when i aply power for the fist time
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Re: warning light question

Postby dadhad1 » Fri Sep 20, 2013 1:25 pm

Hey Vegadude,
Totally off topic, but can you tell me where to find or send me a high res version of your Avatar?
That pic is so damn cool, it's worthy of a big print, frame, and hang in the garage !

Mike
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Re: warning light question

Postby cjbiagi » Fri Sep 20, 2013 2:20 pm

There is a difference between a "sender" and a "switch". A sender provides a variable resistance for the ground circuit and is generally used with a gauge. Most gauges or similar devices do have 3 wires. One is the 12v, another is a ground, and the third is the variable resistance provided from the sender.
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Re: warning light question

Postby cosvega76 » Fri Sep 20, 2013 4:55 pm

Which sender are you referring to?

The oil pressure sender circuit is unique in the Vega, because of the electric fuel pump. One terminal is connected to the start circuit between the ignition switch and the starter, one is from the oil light on the dash, which is also connected to the fuel pump, and one is connected to the Fuel Pump Run fuse (12v switched). With no oil pressure, the fuel pump/oil light circuit is connected to the starter circuit. Energizing the starter sends power to the fuel pump via the fuel pump/oil light circuit through the Fuel Pump Start fuse. Once oil pressure is established, the oil pressure switch connects the fuel pump/oil light circuit to the Fuel Pump Run fuse circuit.

Since there is power on both sides of the oil light, it does not illuminate. If the oil pressure drops below the threshold, the connection breaks between the Fuel Pump Run and fuel pump/oil light circuits and the oil light is grounded through the fuel pump and/or starter solenoid. Since there is little current supplied because of the resistance in the light bulb, there isn't enough to supply either the starter or fuel pump and does not energize either one.

Believe me, it took me a long time to figure this one out! Pretty ingenious circuit design!


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Re: warning light question

Postby vegadude » Fri Sep 20, 2013 8:48 pm

ok so if im not goin to use the factory fuel pump wiring and im using single terminal sending switchs for oil and water should i diconect those wires?
the alt light i understand the reson for the 3rd wire is so it will still charge even if the bulb is dead or missing
if for any reason nobody uderstands what im talking about look at the wiring diagram at bulkhead conector interior side you will see the wires from the sender swichs slpit off to the ign
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Re: warning light question

Postby vegadude » Fri Sep 20, 2013 11:50 pm

hey dadhad pm me
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