Oil pressure safety bypass switch - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Electrical
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 03-23-2010, 09:24 PM
boris_thespider's Avatar
Registered User
 
Last photo:
Join Date: Dec 2009
Location: Lewiston, NY
Posts: 54
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Oil pressure safety bypass switch

I have a low oil pressure safety switch wired into my fuel pump relay circuit. I want to have a momentary bypass switch so the fuel pump can start running before I crank the starter. I wired the bypass switch across the safety switch common terminal (where it attaches to fuel pump relay) and the normally open terminal (where it connects to the ignition hot key). When I pushed the bypass button (with the key in the ON position), my starter turned over?!? When I looked at my wiring diagram, it appears that the bypass connection allowed power to back feed through my solenoid connection on the safety switch and cranked my starter I've seen diagrams that show the bypass switch connected the way I have it, so I think my safety switch/solenoid wiring is messed up. HELP!!! Has anyone ever had their starter turn over when pushing the bypass button?

Mike

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 03-24-2010, 07:44 AM
cboy's Avatar
Member
 

Last journal entry: Finished
Last photo:
Join Date: Jan 2004
Location: Atwater, CA
Age: 69
Posts: 3,915
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
I don't want to mess up your thread but I'm wondering if someone can explain how the low oil pressure safety circuit actually works. I have a wire for the low pressure switch off the ignition switch (79 Ford F-100) but when I test for continuity across all the other pins on the ignition switch, none of them seem to connect up to the wire for the low pressure switch. In other words, I can't see any indication that the wire from the low pressure switch would have any way of preventing the engine from firing or running...or doing anything else for that matter.
__________________
Always learning...and sharing what I've learned. The Scratch-Built Hot Rod.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 03-24-2010, 08:08 AM
delawarebill's Avatar
Registered User
 
Last photo:
Join Date: Mar 2009
Location: delaware
Posts: 1,202
Wiki Edits: 0

Thanks: 14
Thanked 58 Times in 58 Posts
safety sw

i wondering why u just didn't put the sw in the coil side of the relay. that way there is no interuption of power to the coil after the b/p sw is turned off...
an oil pressure sw is used in series of the fuel pump power lines. in the case of veh turn over or accident the motor will turn off and when your oil pressure drops below a point so does the fuel pump... don't need to feed a fire.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 03-24-2010, 08:20 AM
boris_thespider's Avatar
Registered User
 
Last photo:
Join Date: Dec 2009
Location: Lewiston, NY
Posts: 54
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I don't know if this answers your question or not, but the way I understand it... you have a wire from solenoid/starter terminal on the ignition switch that goes the normally closed side of the oil pressure safety switch. When there's no oil pressure, the starter wire is connected directly to the fuel pump(or fuel pump relay). This allows current through the safety switch when the engine is first cranked. Then when you have oil pressure, the safety switch switches to the normally open side which is connected to the "hot" key part of the ignition switch which allows the fuel pump to keep running. Then if you lose oil pressure, it switches back to the normally closed side of the safety switch, killing the power to the fuel pump.

Unless, someone can help me with this bypass circuit... I think I'll just leave the bypass switch out and I'll just have to crank a little longer to get gas to the carb.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 03-24-2010, 08:23 AM
boris_thespider's Avatar
Registered User
 
Last photo:
Join Date: Dec 2009
Location: Lewiston, NY
Posts: 54
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
DelawareBill...
Where in the fuel pump relay circuit would you put the bypass? The bypass switch I have is a momentary on switch... then it returns to the off position.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 03-24-2010, 08:48 AM
cobalt327's Avatar
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 59
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 597 Times in 546 Posts
I'm sure that w/the right switch and wiring, the low pressure switch will work as you want it to.

If the switch doesn't have the capability of priming the pump, you can use a press button, momentary on switch to a relay, wired to prime the pump b/f start-up.

That said- there are a LOT of vehicles, both OEM and "others" that do not have the fuel pump wired to a low pressure switch, w/the exception of nitrous cars that will use such a switch to shut down the engine if the fuel pressure drops.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 03-24-2010, 09:34 AM
cboy's Avatar
Member
 

Last journal entry: Finished
Last photo:
Join Date: Jan 2004
Location: Atwater, CA
Age: 69
Posts: 3,915
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
So if you have a mechanical fuel pump, does the low oil pressure switch do nothing? Perhaps that is why my wire from the low pressure switch seems to go nowhere at the ignition switch.
__________________
Always learning...and sharing what I've learned. The Scratch-Built Hot Rod.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 03-24-2010, 10:56 AM
T-bucket23's Avatar
Hotrodders.com Moderator
 
Last wiki edit: Engine basic condition - how to check Last photo:
Join Date: Aug 2005
Location: Massachusetts
Age: 56
Posts: 5,084
Wiki Edits: 26

Thanks: 7
Thanked 100 Times in 86 Posts
Quote:
Originally Posted by cboy
So if you have a mechanical fuel pump, does the low oil pressure switch do nothing? Perhaps that is why my wire from the low pressure switch seems to go nowhere at the ignition switch.
If you wanted to get creative you could wire it into your ignition feed to kill the ignition if oil pressure was lost.
These circuits were designed for cars with fuel injection that will die as soon as the fuel pump is shut down. A carburetated car will still run until the bowl is dry so it is not as effective.
Killing the ignition would actually be safer.
Also a bypass should be wired to the starter circuit to provide a bypass while cranking automatically.
__________________
Artificial Intelligence is no match for Natural Stupidity



Chet
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 03-24-2010, 03:41 PM
Rickracer's Avatar
ASE Master Tech, Fabricator
 
Last wiki edit: Taurus 2-speed fan control wiring diagram Last photo:
Join Date: Jan 2010
Location: Kissimmee, Florida
Age: 55
Posts: 936
Wiki Edits: 8

Thanks: 0
Thanked 3 Times in 3 Posts
If it's a GM, you could use the outside terminal on the starter to power the pump while cranking,
Reply With Quote Quick reply to this message

Recent Electrical posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Question on oil pressure switch with electric choke grobb284 Electrical 6 05-05-2009 08:33 PM
camaro oil pressure switch? sexypizzaman Engine 3 05-24-2008 12:32 PM
Oil Pressure Switch and Temp Sending unit jvgrago Engine 5 05-23-2008 09:38 PM
Wiring Neutral Safety Switch / EZ-Wire Kit horvath Electrical 15 01-20-2008 12:35 PM
No Oil Pressure!! MartyMart9@aol.com Engine 43 04-26-2005 06:37 AM


All times are GMT -6. The time now is 04:28 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.