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75 Duster - need help

Discussion in 'A Body: Duster, Valiant, Dart, etc' started by jmas11, Jun 5, 2017.

  1. jmas11

    jmas11 New Member

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    Mounted On the inside center drivers side fender wall, between the ign. mod. & another electrical relay, is a 'vacuum actuated electrical switch'. The nipple broke off and I need to replace the unit (no part # on it), and cannot trace the wiring to it's end. Can anyone tell me what this switch is for??
    Appreciate any help!

    thanx
    jmas
     
  2. ImperialCrown

    Level III Supporter

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    Welcome to Allpar. What color codes are on the wires? Is it a manifold vacuum hose and where does the hose go?
     
  3. valiant67

    valiant67 Rich Corinthian Leather
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    Without seeing it, my guess is EGR related.
     
  4. jmas11

    jmas11 New Member

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    Thanks for the quick response!!!
    Vacuum hose, 5/16"id, with white stripe runs straight from manifold to vacuum operated elect. switch .
    Wires on switch (with tan plastic diaphragm cover) are solid black & solid green and plug into relay (that is mounted next to it) . Wire coming out of that relay are solid black and black with yellow stripe and dissappear into the morass of wiring that is hidden from view........
     
  5. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    It could be EGR. Relay would control solenoid opening and closing the vacuum port in the switch.
    Or it could be a purge solenoid, opening and closing vacuum to the evaporative emissions canister, so that under certain conditions, the mixture is enriched by drawing off vapors from the charcoal canister. It should be one of the two.

    But as I recall, EGR had a temperature-controlled vacuum switch that screwed into the head, so that when cold, no vacuum was applied. Will have to look at my old Petersen's book tonight.

    How many vacuum ports are on the vacuum switch, and where do the existing hoses run to and from?
     
  6. ImperialCrown

    Level III Supporter

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    If it is just the one hose and you have fender mounted turn signal indicators, this could be the Fuel-minder switch that lights the LF fender indicator when you accelerate rapidly?
    It was to train drivers to try keep the intake manifold vacuum high and get better mpg.
     
    pt006 and Bob Lincoln like this.
  7. jmas11

    jmas11 New Member

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    Thanx folks - good info!
     
  8. pt006

    pt006 Active Member

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    jmas; The relay you mentioned shows up as a double diode and resistor combination from a 1976 diagram. Possible ?
     
  9. jmas11

    jmas11 New Member

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    Well, since there a was previous owner, anything is possible.
     
  10. pt006

    pt006 Active Member

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    I.C. mentioned a fuel minder switch. This sounds right. You mentioned a relay. The wiring diagram does not show a relay. It shows a double diode and a resistor instead.
     
  11. ImperialCrown

    Level III Supporter

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    The relay or an isolation diode could be used to override the Fuel-minder for turn signal operation. (i.e. - when signaling and accelerating at the same time to pass someone on the left). You couldn't have both systems working at the same time.
     
  12. pt006

    pt006 Active Member

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    The two diodes are pointed at each other, And in between them there is a wire going to the top fender light filament. One diode is fed by the vacuum switch. The other diode is fed by the left blinker switch. So electricity cannot be fed from one switch to another. My guess is that the resistor makes the fuel light dimmer than the blinker light. Not sure.
     
  13. jmas11

    jmas11 New Member

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    The relay I mentioned, next to, and connected to the part in question does have some #'s on it:
    3764343 and below those #'s are 58304. It was hard to make these out - hope they are correct.
     
  14. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    from eBay - "1974-75 Chrysler Plymouth Dodge Fuel Pacer Relay 3764343"
     
  15. jmas11

    jmas11 New Member

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  16. jmas11

    jmas11 New Member

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    Thanx again people!!!
    Found the switch on E-bay, got it yesterday and it works as advertised, although it gets distracting as my foot is usually in the hole quite a bit......
     
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