I am wiring my electric fuel pump with an oil pressure safety switch, and on the safety switch it says to wire it to the starter as well. However, which wire do i want to hook it up to?? I know there are 3 terminal on the starter, but which one is only hot when the starter is engaged?? The one closest to the block??

Thanks
Chris


[Modified by 74VETTE, 6:04 PM 2/8/2002]

 

I am assuming the manufacturer wants you to wire the oil pressure safety switch into the run wire on the starter, so in case of low oil pressure, it cuts power to your ignition run wire (not the start wire). This would be the purple 12 guage wire. I don't think they want to cut power to the start wire, because you are not going to get high oil pressure while turning the car over.

AC

 

A C, I dont believe it is to cut power to the igntion, but to allow the fuel pump to run (bypass the safety switch) only while starting.......otherwise the fuel wouldnt ever get to the carb....

Chris

 

Chris,
You arte correct the switch is to cut power to the pump not ht e ignition. I have this preasure switch on my 74 with a Holley blue pump. I looked at the directions last night to see if I could tell you how I hooked it up, but I could not remember. I would have to go out and look at the car and see how I wired it. I do remember I hooked up the iginition wire to the fuse box. I just cant remember how I hooked it to the solenoid. If you dont get a response from anyone else I will take the wires apart and take a look. This is a very worth while saftey steep, and the switch works well.
Ed

 

Chris,
I looked at my solenoid and it looks like I have on the S terminal of the solenoid. If you really want to make sure you can give them a call on their tech line 270 781 9741. Holley does not do a good job with their instruction sheets. The graphics are poor copies and do not give you propper detail. You should not have to guess what terminal to hook up to the soleniod. I found an error in their wiring diagram for my Annihilator ignition. Let me know how you make out. Sorry for the poor type job in the last post. I guess it was early.

Ed

 

Thanks ED, Holley directions definitely are weak, but ill figure it out for a good product IMO. Definitely a good "insurance" product in case anything goes wrong.

I dont know what you mean by the s-terminal tho. :troll Im pretty sure its the one in the back of the block cause the main wire frmo the battery obviously has 12V, but it gets itwhen i test the ground to the other terminal to the outside of the motor. Leaving the inside terminal, but ill disconnect the igntion wires and have someone turn it over while i check to makre sure
Thanks
Chris


P.S. ED, i see you are in North Brunswick. I am only a littleways from you. Are you going to the police departments show hosted in Devry, and i think its sometime in march or april??

 

The "S" terminal is the small terminal closest to the block. The "R" terminal is the little one closest to the fender. :)

 

74Vette,
When you get this all figured out and hooked to the correct terminal on the starter....could you please give a holler over here so I can hook my switch to the proper terminal.....mine had no directions included with the switch. I also need to know which terminal to hook up one of my radiator fans to.

 

I didn't hook the oil pressure switch to the starter. I figure that there IS fuel in the carb and the 3 seconds it takes to start the car I really don't need the fuel pump running...

I have run like this for 2 years and it works well. If the car IS having a hard time starting the oil pressure does come up anyway to allow the pump to run.

BTW when you prime the carb, it's best to 'bump' the pump is it doesn't slam th floats and screw them up. Some people even fill the carb with a funnel through the vents...

 

Chris,
The S terminal is the on closest to the block, it goes to the iginition switch. If you could see the solenoid it has a S stamped on it.
The other terminal goes to the coil. I will probable go to the cops and rodder show a devry in april. Its 1 mile from my home. Hope to see you there.
Ed

 

Thanks everyone for helping me out....I put the wire on the S- terminal, and it was definitely high on the royal PITA scale! Wasted my time trying to get it from the top and finally gave up and dropped the started down to do it.

Ed, ill be at the show at devry...already registered...cya there. Someone told me they allow burnouts in the parking lot and the cops dont bother anyone??? I hope so :D

 

Chris,
The cops dont bother you, they just give you a ticket and smile. It also helps the tax rate for which I appreciate. How did you do with the wireing of your switch?
Ed

 

This may be a little late, but here's the explanation.
The hobbs switch is there to shut off the fuel pump in case the engine dies (it's bad to have fuel flowing after an accident or if the car flips). It switches off the fuel pump if the oil pressure gets under 6-7psi. It screws into the block anywhere there is a pressurized source, ie. a T off the oil pressure line or one of the unused cooler outlets on the Gen V BBC.
It has 3 posts/spades on it. One is the output to the pump. The other 2 inputs go to 1) a keyed ignition source (run position) and 2) the ignition switch "cranking" (start position).
The start post is connected to the pump with no oil pressure. When the engine is cranking, this allows current to flow to the pump. This fills the bowl even when the engine has not yet started or built up pressure.
As the engine fires and oil pressure increases the switch opens from the start position and closes over to the run position. This supplies power to the pump from a keyed ignition source. If the engine should die and loose oil pressure, the switch goes back to the start position and no current gets to the pump.
A couple of notes. DO NOT use the bypass output terminal from the starter solenoid, only the start post from the ignition. This can allow current to flow from the from the ignition switch to the coil, then to the start position on the hobbs switch. The engine will run, but it will not shut off in case of engine shutdown.
Check to see you have good voltage at the pump, low voltage has a habit of burning out pumps prematurely.Too many keyed accessories, radio, solid state ignitions, electric chokes, etc can overwhelm the circuits capacity. Even if it doesn't blow fuses, it may result in low voltage at the pump. Same is true with a too small of wire. Use a relay to a fused battery 12V source.
And I trust you did read the directions and mount the pump low and close to the fuel tank. To high or far away will kill pumps too.
My $0.02
Gary

 

Thanks ED...now i know not to do any burnouts....

As far as the fuel pump, here is what i got done so far....not much...spent maybe at the most 2 hours, so not too far.....
Installed the relay close to the battery, as well as the circuit breaker per instructions from Painless.
Installed safety switch in side of block with a "tee" for original sending unit for gauge and made sure it cleared all the clutch linkage, engaged and disengaged. Ran the "common" wire back to the relay.
And wired it to a switched current as well as the S terminal on the block.

All thats left is mounting the pump, and hooking the wires up that are already waiting where it will be mounted, which is cose to the tank, on the frame, which i believe is lower than the tank as well.

Garys '68, i dont understand what you mean by not putting it on the bypass output terminal on the solenoid....is that the S-terminal others are talking about?? And since i have no traditional coil (HEI w/ MSD 6AL), where should i hook it up to you in your opinion?

As far as not enough voltage, i probably have this problem, but Im planning on a high amp alternator in the spring anyway.

Chris

 

Thought I'd say this about mounting fuel pumps...

Look at Merlins fuel pumps, this a very good example of where NOT to mount pumps!

Pumps and lines should be protected from road debris and flying parts. If merlin were to blow a tire at highway speed it could easily take off a pump which would cause the fuel to be pumped onto the wheel which is now shooting sparks like the 4th of July...

I put mine on the rear crossmember just in front of the tank The pump and the filter are mounted onto a thick piece of sheeetmetal which is then mounted to the crossmember. The lines run along and behind the crossmember to protect them from the half shafts and road debris.

 

If I remember right, your ignition setup does not use a ballast resistor or wire. It gets a full 12V from the ignition all the time and no bypass wire from the solenoid is used. You should be OK with that setup as long as you've disconnected the original wire that ran from the solenoid to the + side of the original coil. The problem I've seen before is that the bypass wire is hooked up and the hobbs swich is hooked to the same solenoid post. This allows current from the ignition to flow to the coil, then to the hobbs switch "s" position and then to the pump, even with no oil pressure present.
As for current to the pump, don't worry about the alternator, it probably has enough capacity. The voltage drop is a result of too small of a wire from the ignition and too many accessories running off of it. You can have a 120 amp alternator, but if you take your feed for the pump from a little 18g wire that runs the ignition, electric choke, etc. it won't be able to supply enough current. I would reccommend fused a 14g feed directly from the ignition to the hobbs switch, then to the fuel pump. It's kind of a long run, so a larger diameter wire is a good idea. As I said before, you could use a relay from a full time fused 12V feed then to the pump.
Gary

 

Thanks 427V8, I was going to mount mine on the frame behind the wheel. I am going to check if there are any problems...if so im gonna try to mount another place....definitely better to be safe than sorry.

Thanks Gary, i should be set then cause i disconnectted all the wires to the coil, and i installed a relay anyway :yesnod:

Chris