H-Body Start Circuit

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H-Body Start Circuit

Postby zeke » Wed Sep 20, 2017 2:31 pm

Battery power is fed to the car through a fusible link from the large starter solenoid terminal.

When the ignition switch is turned on, power flows to the oil light and to ground through the fuel pump so light turns on.

When ignition switch is turned to start, power flows through the neutral safety switch, or clutch switch, to the normally closed contact (NC) on the pressure switch. Power flows out of the common (C) terminal, through the fuel pump fuse and to the fuel pump - carb gets primed. Power also flows to the S terminal and starter engages.

When the engine starts, oil pressure causes the 3 terminal switch to connect the common and normally open contacts (NO) and disconnect from the NC terminal. Power now flows from the ignition switch to the fuel pump and pump stays running when the key is turned back.

Oil light now has +12 volts on each side - zero volts, and goes out.

In the event of a crash or rollover, pressure switch drops out and power to the fuel pump is disconnected. This ensures that the fuel pump doesn't feed any fire.

For testing purposes, you can jump the pink and dark blue wires at the oil pressure switch connector, fuel pump should run when the key is turned to on. Not a good idea to leave it this way though.
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Re: H-Body Start Circuit

Postby zeke » Wed Sep 20, 2017 3:41 pm

Connector pigtail: STANDARD MOTOR PRODUCTS S956
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Re: H-Body Start Circuit

Postby Monza Harry » Wed Sep 20, 2017 5:00 pm

zeke wrote:Connector pigtail: STANDARD MOTOR PRODUCTS S956
Chris I had posted that up here awhile ago, and then it went missing from RA's site, Glad to see that it has returned! It looks pretty similar to my original one and fit nicely on a replacement Oil pres. sw. [OEM style] With that and some die electric grease one should be "Golden" :th: Harry
I'm not a hoarder I'm a preservationist 78 Monza Spyder (Soon To Be 2+2 with Spoilers)
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Re: H-Body Start Circuit

Postby mikebrow74 » Mon Oct 16, 2017 11:07 pm

Is the Oil Pressure Switch/Sender different for the oil gauge vs idiot light?
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Re: H-Body Start Circuit

Postby zeke » Mon Oct 16, 2017 11:19 pm

An aftermarket oil pressure gauge would need a separate sender unit.
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