gearheadstik Posted August 22, 2007 Share Posted August 22, 2007 I'm in the process of doing a little rewiring and would like to find out what the under hood relays are to... There a 4 of them under the relay cover and I think through wiring dia.... They are 2 fuel pump relays, 1 AC relay and I can't figure the other out... It has 5 blue wires and 1 green wire... Is it the ignition relay? Thanks Quote Link to comment Share on other sites More sharing options...
COZY Z COLE Posted August 23, 2007 Share Posted August 23, 2007 Look at Fig.20... EFI relay.....http://www.autozone.com/az/cds/en_us/0900823d/80/1d/1d/80/0900823d801d1d80/repairInfoPages.htm.. LARRY Quote Link to comment Share on other sites More sharing options...
gearheadstik Posted August 23, 2007 Author Share Posted August 23, 2007 DDDDuuuuhhhh... You know I had looked over this already and missed it, Thanks and these are nice and a heck of a lot easier than trying to magnify the haynes manuals. One more quick thing, Why 2 fuel pump relays? I'm very weak on wiring issues. Quote Link to comment Share on other sites More sharing options...
COZY Z COLE Posted August 23, 2007 Share Posted August 23, 2007 If you notice the second relay is connected to the oil pressure sending unit. If my memory is correct it's a safety feature so that if you are in an accident and the engine stops your oil pressure would go to zero and this relay would shut off the relay running the fuel pump. This is so if you have a fuel line break there would be no fuel being pumped from the gas tank in case of a fire. Someone else can correct this if I'm wrong... LARRY Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted August 30, 2007 Share Posted August 30, 2007 If you notice the second relay is connected to the oil pressure sending unit. If my memory is correct it's a safety feature so that if you are in an accident and the engine stops your oil pressure would go to zero and this relay would shut off the relay running the fuel pump. This is so if you have a fuel line break there would be no fuel being pumped from the gas tank in case of a fire. Someone else can correct this if I'm wrong... LARRY IF you mean the single wire oil pressure switch like my 77 has, then that must be wrong. I removed mine to install an Autometer oil pressure gauge with no ill effect. Quote Link to comment Share on other sites More sharing options...
COZY Z COLE Posted August 30, 2007 Share Posted August 30, 2007 78-81NA....When the engine is not running the oil pressure switch is closed and the transistor at the 'L' terminal of the alternator is "closed" and BOTH idiot lights for ALT and OIL are ON. When the key is turned to ON the idiot lights are on and the fuel pump is OFF. The fuel pump only "starts" when the key is turned to Start. These years used three relays to control the fuel pump. If the engine stops / stalls the loss of BOTH ALT and OIL signals simultaneously shuts off the fuel pump. LARRY Quote Link to comment Share on other sites More sharing options...
Stealth-Z Posted August 30, 2007 Share Posted August 30, 2007 IF you mean the single wire oil pressure switch like my 77 has, then that must be wrong. I removed mine to install an Autometer oil pressure gauge with no ill effect. From 1977 back to 1975 the AFM had the safety fuel cut feature. On these years you could turn the key on, remove the plasic cover on the AFM, then rotate the AFM mechanism to turn on the fuel pump. In 1978 they changed the fuel safety cut to route off the oil pressure sending unit. Same principle as the AFM method, no air flow, no need to continue fuel pressure, no oil pressure, definetly do not want to continue fuel! As Larry points out with the alternator & oil signals, there is a redundency in the system. Quote Link to comment Share on other sites More sharing options...
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