It looks like 12 volts is always on the radio and 12 volts will go to the device if momentary switch is pressed and held. So, 12 volts will energize the pump as needed. If you put a meter on the 12 volt line as you energize the device, does voltage go away completely. ?
Need Help with an Electrical Issue (1 Viewer)
- Thread starter 1979 FJ40ish
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I just noticed the battery in your diagram... That isn't the truck battery is it? Power should be coming from the other side of the fuse panel, so why is there a battery attached to the radio?
It looks like he has a yellow wire going to the radio from another wire for constant 12 volts for radio time and memory. The one from fuse panel is on/acc power to the radio. He shows a MOMENTARY switch to a device/pump. Only thing I can tell is a problem with the pump ?
- Thread starter
- #24
The yellow wire is connected directly to the FJ battery per the radio installation instructions for constant power. I assume this is to maintain station memory and time when the FJ is shut off. Also per the instructions the red wire is energized when the ignition is turned on.
It is a Holley Mighty Mite Electric Fuel Pump 12-426.
It is a Holley Mighty Mite Electric Fuel Pump 12-426.
Are you wiring this according to the Holley instructions?
This instruction specifically says to use a relay, if you aren’t using an OPSS... I don’t see an OPSS in your diagram.
The fact that they specifically say to use a relay suggests the same concern @Living in the Past expressed... the chance of overloading an OLD ignition and OLD wiring... be warned.
IIRC you are fusing your device at 5 amps.
Is the radio circuit still fused at 5 amps?
Holley’s 3-5 amp requirement suggests the pump could draw the full 5 amps at times.
How much does the ignition-side of the radio draw?
I’m a twice retired software developer... not an electrical expert. I don’t recall all of my high school electronics... yes, we had electricity in the mid 60s
But, resistance is a major player... since you split your (diagramed) circuit into two circuit branches, which branch is physically shorter?
Since the radio circuit is 5 amps and the pump can draw 5 amps, it seems possible that the pump is the physically shorter fragment, drawing too much to allow the radio to remain powered on. This would explain why the radio shuts off.
This test appears to confirm that the above is your radio shutoff problem.
Regarding the switch and pump, you also said “The device shuts off when the button is released. The device will NOT be used when the engine is running.”.
If your device is a fuel pump, I don’t understand how the fuel pump will not be used with the engine running.
Regardless, I suspect the switch switch/device issue is also a result of splitting this 5 amp radio circuit.
You (Edit: still using the radio circuit) could fairly quickly eliminate potential wiring/ignition overload and provide a dedicated battery+ power circuit, to the switch/pump by simply wiring a relay into your RB fragment, between the switch and the device.
I’m sure that would solve your radio issue and am relatively sure the relay would also solve your device issue.
Good luck
BTW
You should SERIOUSLY consider adding an OPSS, if the pump is used to pump fuel, while driving.
The OPSS will shut the pump down anytime the oil pressure drops below 2psi... but, will allow you to start the engine, with oil pressure below 2psi.
It could prevent burning down you and your 40, in the event of an accident.
This instruction specifically says to use a relay, if you aren’t using an OPSS... I don’t see an OPSS in your diagram.
The fact that they specifically say to use a relay suggests the same concern @Living in the Past expressed... the chance of overloading an OLD ignition and OLD wiring... be warned.
“7. Connect the RED (positive) power lead to the OPTIONAL OIL PRESSURE SAFETY SWITCH
or
TO A RELAY CONTROLLED
BY IGNITION. If this pressure switch is not available, connect to the ignition switch voltage supply terminal.”
You said, you’ve fused the momentary switch circuit fragment in accordance with the Holley “3-5 amp” directive, on a 5 amp radio circuit.or
TO A RELAY CONTROLLED
BY IGNITION. If this pressure switch is not available, connect to the ignition switch voltage supply terminal.”
IIRC you are fusing your device at 5 amps.
Is the radio circuit still fused at 5 amps?
Holley’s 3-5 amp requirement suggests the pump could draw the full 5 amps at times.
How much does the ignition-side of the radio draw?
I’m a twice retired software developer... not an electrical expert. I don’t recall all of my high school electronics... yes, we had electricity in the mid 60s
But, resistance is a major player... since you split your (diagramed) circuit into two circuit branches, which branch is physically shorter?
Since the radio circuit is 5 amps and the pump can draw 5 amps, it seems possible that the pump is the physically shorter fragment, drawing too much to allow the radio to remain powered on. This would explain why the radio shuts off.
This test appears to confirm that the above is your radio shutoff problem.
“With the ground wire removed from the device:
One lead of the mulitmeter connected to a good ground on the body
The other lead connected to the input of the device
12V at the device
The radio DOES NOT cut off
The device will not work because it is ungrounded”
One lead of the mulitmeter connected to a good ground on the body
The other lead connected to the input of the device
12V at the device
The radio DOES NOT cut off
The device will not work because it is ungrounded”
Regarding the switch and pump, you also said “The device shuts off when the button is released. The device will NOT be used when the engine is running.”.
If your device is a fuel pump, I don’t understand how the fuel pump will not be used with the engine running.
Regardless, I suspect the switch switch/device issue is also a result of splitting this 5 amp radio circuit.
You (Edit: still using the radio circuit) could fairly quickly eliminate potential wiring/ignition overload and provide a dedicated battery+ power circuit, to the switch/pump by simply wiring a relay into your RB fragment, between the switch and the device.
I’m sure that would solve your radio issue and am relatively sure the relay would also solve your device issue.
Good luck
BTW
You should SERIOUSLY consider adding an OPSS, if the pump is used to pump fuel, while driving.
The OPSS will shut the pump down anytime the oil pressure drops below 2psi... but, will allow you to start the engine, with oil pressure below 2psi.
It could prevent burning down you and your 40, in the event of an accident.
I should ask... is your momentary switch Completing the circuit (use relay 87) or opening the circuit ( use relay-87a instead)?
- Thread starter
- #28
Guys – thanks for all your help but let me throw another curve ball.
As I noted above but perhaps not clearly enough I intend to use the pump to prime the carb BEFORE starting the engine. Even though I’ve spent nearly $1,000 to have a rebuilt OEM carb installed on it, it continues to suffer from the same problem others have reported in this forum -- if the FJ sits for a period of time undriven it will not start without priming the carb.
Since the pump will only be used for a few seconds I opted to use a momentary switch that will only energize the pump while the switch is physically pushed (I’m thinking 3 – 5 seconds).
Since the switch is mounted on the dash I initially picked the lead between the fuse box and the radio because it is on a 5 amp fuse and because it was energized only when the ignition was on and would not operate if someone (a kid) got in and began pushing buttons without the key.
Earlier today I disconnected the input lead to the switch (the wire that splits off from the wire between the fuse box and the radio).
I connected the input side of the switch to a test lead directly from the positive side of the FJ battery.
The pump and the radio both worked.
In one place the pump installation instruction state to connect it using a 3 – 5 amp fuse in another it says use a 3 amp fuse. The pig tails out of the pump are at best 16ga and possibly even 18ga wire. I’m assuming, given this info the pump is not going to draw a lot of current.
Below is a graphic showing how I now plan to wire the pump. Does anyone see a reason this will not work? Yes, I know the pump will run whenever the switch is pushed.
I think (I hope) I’m about at the end of a three-year long restoration effort. I would not have been able to complete this project without the assistance of this forum and folks like you that take the time to assist rookies like me. It is greatly appreciated!
As I noted above but perhaps not clearly enough I intend to use the pump to prime the carb BEFORE starting the engine. Even though I’ve spent nearly $1,000 to have a rebuilt OEM carb installed on it, it continues to suffer from the same problem others have reported in this forum -- if the FJ sits for a period of time undriven it will not start without priming the carb.
Since the pump will only be used for a few seconds I opted to use a momentary switch that will only energize the pump while the switch is physically pushed (I’m thinking 3 – 5 seconds).
Since the switch is mounted on the dash I initially picked the lead between the fuse box and the radio because it is on a 5 amp fuse and because it was energized only when the ignition was on and would not operate if someone (a kid) got in and began pushing buttons without the key.
Earlier today I disconnected the input lead to the switch (the wire that splits off from the wire between the fuse box and the radio).
I connected the input side of the switch to a test lead directly from the positive side of the FJ battery.
The pump and the radio both worked.
In one place the pump installation instruction state to connect it using a 3 – 5 amp fuse in another it says use a 3 amp fuse. The pig tails out of the pump are at best 16ga and possibly even 18ga wire. I’m assuming, given this info the pump is not going to draw a lot of current.
Below is a graphic showing how I now plan to wire the pump. Does anyone see a reason this will not work? Yes, I know the pump will run whenever the switch is pushed.
I think (I hope) I’m about at the end of a three-year long restoration effort. I would not have been able to complete this project without the assistance of this forum and folks like you that take the time to assist rookies like me. It is greatly appreciated!
I don’t see why that won’t work the way you’ve described.
But, there’s a right way and an easy way...
I would never want an electric fuel pump that could be activated with the ignition off... even with a switch controlling it... Murphy’s Law.
On another note, I don’t understand why some MUDders have a problem priming their carb. I never had that problem, with my oem pump.
It seems like the oem pump should prime the carb as long as you crank the ignition.
Is the oem pump taking too long a time to prime the fuel lines and carb?
A few years ago, after encountering a hole in my oem pump diaphragm, I pulled my oem pump and installed an electric pump on each tank.
That eliminated potentially dumping fuel in the crankcase and provided me an instantaneous fuel backup, as long as I keep gas in both tanks... just flip to the other pump/tank, if one fails.
If you are going to the trouble to add an electric pump, to prime the carb, you could have just about as easily removed the mech pump and used the electric pump full time.
But, to each his own.
Cheers
But, there’s a right way and an easy way...
I would never want an electric fuel pump that could be activated with the ignition off... even with a switch controlling it... Murphy’s Law.
On another note, I don’t understand why some MUDders have a problem priming their carb. I never had that problem, with my oem pump.
It seems like the oem pump should prime the carb as long as you crank the ignition.
Is the oem pump taking too long a time to prime the fuel lines and carb?
A few years ago, after encountering a hole in my oem pump diaphragm, I pulled my oem pump and installed an electric pump on each tank.
That eliminated potentially dumping fuel in the crankcase and provided me an instantaneous fuel backup, as long as I keep gas in both tanks... just flip to the other pump/tank, if one fails.
If you are going to the trouble to add an electric pump, to prime the carb, you could have just about as easily removed the mech pump and used the electric pump full time.
But, to each his own.
Cheers
This post reflects exactly my questions. I can leave my FJ40. 1969, for months and a few cranks and pushes on the accel pedal, and a start. I agree there is a deeper issue if one wants a prime deal instead of getting down to what the real issue is.
I also heard todays fuel is hard on gaskets ? Not sure if that is true, but an OEM fuel pump may have fallen victim to that.
bj40green
Tssss, tssss
Here are my thoughts:
A pump or any electrical motor has a run-in current, that's the current to get the pump motor moving.
Have you ever noticed that the light dips for half second when you turn on your circular saw?
You have a 5Amp fuse which will blow at 1,2 the nominal value.
The run-in current from the pump is not high enough to blow the fuse (Fuse is a resistor that burns at a specific current) but the effect is that the fuse becomes a resistor which causes a voltage drop.
Solution: replace the fuse for a 10Amp and see if it works. If it works....... you found the problem!
Another possibility is that the fuse holder contacts are rusty (and thus acts as a resistor) or your fuse is decades old.
Just my thoughts,
Rudi
A pump or any electrical motor has a run-in current, that's the current to get the pump motor moving.
Have you ever noticed that the light dips for half second when you turn on your circular saw?
You have a 5Amp fuse which will blow at 1,2 the nominal value.
The run-in current from the pump is not high enough to blow the fuse (Fuse is a resistor that burns at a specific current) but the effect is that the fuse becomes a resistor which causes a voltage drop.
Solution: replace the fuse for a 10Amp and see if it works. If it works....... you found the problem!
Another possibility is that the fuse holder contacts are rusty (and thus acts as a resistor) or your fuse is decades old.
Just my thoughts,
Rudi
I suggest removing the fuse and cleaning the fuse clips, also the connector from the fuse on the back of the fuse panel. This sounds to me like the pump draws enough current that it is dropping a lot of voltage across a corroded/dirty connection at the fuse panel. That explains why you are losing the radio when you push the button and why the pump works when connected directly to the battery. What BJ40green stated above.
I have to do this every couple of years with my headlights when they stop working.
I have to do this every couple of years with my headlights when they stop working.
- Thread starter
- #33
For what its worth the fuse and the fuse box terminals are it great shape.
Regarding the priming issue - apparently I'm not alone based on the research I did on this site. Ive tried every combination of pumping the pedal or not pumping the pedal, choking it or not choking. But once I can no longer see fuel through the little round window in the front of the carb the only way I can get it started is to pour an ounce of fuel into the carb and it will start right up and run fine.
The PO said he put a new OEM mechanical pump on it just before I purchase the FJ. I spent a bunch of money to have a rebuilt OEM carb put on it by a shop I've come to trust over the years and it still has the problem.
I don't like doing what I'm attempting to do but no one seems to have a definitive fix to the starting problem.
Regarding the priming issue - apparently I'm not alone based on the research I did on this site. Ive tried every combination of pumping the pedal or not pumping the pedal, choking it or not choking. But once I can no longer see fuel through the little round window in the front of the carb the only way I can get it started is to pour an ounce of fuel into the carb and it will start right up and run fine.
The PO said he put a new OEM mechanical pump on it just before I purchase the FJ. I spent a bunch of money to have a rebuilt OEM carb put on it by a shop I've come to trust over the years and it still has the problem.
I don't like doing what I'm attempting to do but no one seems to have a definitive fix to the starting problem.
Could you be shutting off the radio because when you activate the pump it draws power backwards from the battery connected to the radio for memory?
This would also be why you are not blowing the fuse... I think you should replace the pump in the diagram with a relay that then runs the pump (have a fused line from the battery to the pump relay directly). I'll bet everything works if you do this...
This would also be why you are not blowing the fuse... I think you should replace the pump in the diagram with a relay that then runs the pump (have a fused line from the battery to the pump relay directly). I'll bet everything works if you do this...
- Thread starter
- #35
Here the thing. I don’t know the difference between relay and a door stop. Not to mention which one to purchase or how to hook it up once I get it home.
My first post shows a picture of a relay and thorough instructions on how to wire it.
My Friday, 7:09pm response, again, explained how to wire you should wire your relay.
My Yesterday, 9:24am response attempted to clarify whether the relay should trigger on closed, or open, circuit.
Many people have tried to help you... all good suggestions... pay particular attention to Rudi (@bj40green ), Yesterday, 9:21pm... he’s an electronics expert.
I hope you work this out.
Cheers
My Friday, 7:09pm response, again, explained how to wire you should wire your relay.
My Yesterday, 9:24am response attempted to clarify whether the relay should trigger on closed, or open, circuit.
Many people have tried to help you... all good suggestions... pay particular attention to Rudi (@bj40green ), Yesterday, 9:21pm... he’s an electronics expert.
I hope you work this out.
Cheers
bj40green
Tssss, tssss
Did you replace the 5Amp fuse for a 10Amp fuse? What's the result?
Another question......
You say the voltage on the fuse RHS in your diagram drops to zero but what happens on the left side of the fuse? Still 12V or does it drop too?
Rudi
Another question......
You say the voltage on the fuse RHS in your diagram drops to zero but what happens on the left side of the fuse? Still 12V or does it drop too?
Rudi
Last edited:
Since its just a primer pump, why not hook it into the starter curcit, so when the motor turns over it prime's, it will take a couple of revolutions but would serve the same purpose and is a much stronger power source,
My guess is the voltage drop thru the wire is causing the issue, you may be seeing 12v with no load but i bet the voltage drops to 3-4v when you try and start the pump causing the issue.. a relay with some larger supply wire would solve the issue if you are stuck wiring it the way you have it...
Its not the wire size its the distance of wire/age. Ford crown vic' have a nice small self contained relay box for the electric fans if you are looking for something clean, has 2 relays in a box with a mounting bracket...
Good luck..
My guess is the voltage drop thru the wire is causing the issue, you may be seeing 12v with no load but i bet the voltage drops to 3-4v when you try and start the pump causing the issue.. a relay with some larger supply wire would solve the issue if you are stuck wiring it the way you have it...
Its not the wire size its the distance of wire/age. Ford crown vic' have a nice small self contained relay box for the electric fans if you are looking for something clean, has 2 relays in a box with a mounting bracket...
Good luck..
- Thread starter
- #39
I've given up trying to diagnosis why the original wiring did not work and will go along with what appears to be the majority opinion - - that with both the radio and the pump running there was too much load on it.
I've reflected on Solaces caution about having a fuel pump that could be activate with the ignition off so I spent some time today trying to figure out how to wire the relay into the equation as Solace recommended. Below is a new diagram incorporating the relay.
Does this proposed wiring look correct? If yes, what type/model of relay should I ask for when I go shopping? I know the one picture above is a Bosch but I assume they make more than one relay.
I've reflected on Solaces caution about having a fuel pump that could be activate with the ignition off so I spent some time today trying to figure out how to wire the relay into the equation as Solace recommended. Below is a new diagram incorporating the relay.
Does this proposed wiring look correct? If yes, what type/model of relay should I ask for when I go shopping? I know the one picture above is a Bosch but I assume they make more than one relay.
You’ve diagramed the switch/pump wiring just like I stated in my Saturday 7:08pm post.
You can buy a 12v relay, in the 12v electronics aisle, at any auto parts or online.
There are four and five terminal relays.
You can use either...
You can use a four terminal relay... it has NO terminal 87a... you don’t need terminal 87a anyway.
You can use a five terminal relay... just don’t use terminal 87a.
You can buy a 12v relay, in the 12v electronics aisle, at any auto parts or online.
There are four and five terminal relays.
You can use either...
You can use a four terminal relay... it has NO terminal 87a... you don’t need terminal 87a anyway.
You can use a five terminal relay... just don’t use terminal 87a.
