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amp light circuit


steevn

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Hey guys, most the guages in my truck stopped working so I replaced them with some auto meter stuff. After putting in the new guages the truck no longer charged. Thats when I discovered the amp light circuit seen here
http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_charging_1991_2.JPG

Its a 510 ohm resistor in paralell with a light, the total resistance is about 95 ohms. So how much resistance does this circuit need? What does the amp light do? Will I burn out the regulator if I just twist the wires together?
 


RonD

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The resistor in parallel with the bulb is so charging doesn't stop if bulb burns out.

What that circuit does is to turn on the alternator/regulator.
If alternator was on all the time it would drain the battery when engine was off.

So when key is turned on there should be 12v on that line, this turns on the regulator/alternator, and the bulb too, as 12v power passes thru it(or resistor if bulb is gone).
Once engine starts and alternator is "working" bulb should go off because alternator is supplying its own 12v so no voltage is flowing thru the bulb, i.e. both ends of that wire have 12volts.

So yes, if it is the gry/y and lg/r wires you are referring to you can just twist them together, but why wouldn't you want a Battery/Charging light??

Key on >>12v>>>>light bulb>>>>regulator

Pretty simple circuit and can warn you if something is wrong.

The reason the 510 ohm resistor is used is so the voltage will pass thru the light bulb first, lighting it up, it has lower resistance than 510 ohms.
 

steevn

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Thanks, I understand it now. I'm gonna make a new amp light.
 

steevn

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Went to radio shack

destroyed the stock resistor so I got these


Key on engine off

engine on
 

steevn

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The new light only had like 5 ohms resistance so I used 150 ohms for the replacement resistor.
 

RonD

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steevn

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Thanks. It was fun makin it.
 

RonD

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Just noticed the oil pressure gauge is showing over 50psi at idle???
Should be about 8psi.

If it is an electric gauge you need to change the sender on the block to a PS60 sender, the one on there now is just a switch.
 

steevn

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It's a mechanical guage. Could it be from a high idle? It was probably idleing around 1200 to 1400 judging from the back side of the tack pointer, which is normal for this truck. Also the engine was cold when I started it there. A couple days ago it was idling normal and the pressure was alot lower, maybe around 20 or less, I didn't pay that close of attention though.
 

RonD

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General "rule of thumb" is 10psi of pressure per 1,000rpm on an older warmed up engine.

Oil pressure is back pressure not pump pressure.
The oil pump delivers a flow of oil thru the oil filter to the main oil passage, where the oil pressure sender is located.
As the oil flow goes out to the crank, cam and the bearings it is restricted by the size of the gaps, this creates a back pressure in the flow, this back pressure is what you see on an oil pressure gauge.
As bearings wear their gap gets bigger so back pressure(oil pressure) is less.

New bearings can raise oil pressure because gap is tighter.

5psi of oil pressure at idle is fine, because it means all bearings are getting oil because there is back pressure, but because of gravity low oil pressure can cause tapping in valve train, so above 8psi is better.

Yes, cold engine with cold thick oil creates higher back pressure until it warms up and oil thins out to 30w.

Too high on oil pressure can cause less lubrication because of spraying at the bearings, also could be a sign of a spun bearing, oil holes on bearing and journal are not lined up creating a higher back pressure.

Yes, under 20psi warmed up at idle(750rpm) would be normal
 

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