So along with thinking about installing a Weber carb (separate thread) I know I’ll have to install a pressure- regulated fuel pump. I was thinking of taking power for the fuel pump from the switched (distributor) side of the ignition switch, possibly through a relay. Has anyone done it this way, or have any other suggestions?
Switched circuit
- Thread starter JayJay
- Start date
Y-Blockhead
Well-known member
John, I think I would re-wire your ignition switch so it is before the coil. This eliminates any possible issues with the ignition circuit. Depending on the current draw of your electric fuel pump, you could then add a relay. Adding a relay will also reduce current flow thru your switch. Not shown in my drawing, I have a fuse in the large red wire going to the relay.
This is the way my switch is wired, minus the relay, to power my Tach. A little more complicated then original, but that is what we get when we start modifying these old girls...
Hope this helps.
This is the way my switch is wired, minus the relay, to power my Tach. A little more complicated then original, but that is what we get when we start modifying these old girls...
Hope this helps.
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stevemclark
Senior Member
Do it that way and it will send pluses of power through the points not a steady voltage .It might overload the points or damage the pump or the relay.
The Master Cylinder
Well-known member
I have my fuel pump wired like Blockhead described in post #2 for years and have had zero issues.
Bob Bidonde
Well-known member
You will need suppression if you have other solid state electronics in your Model A's circuits. When a relay is used, it good practice to use a diode to suppress the relay coils collapsing induction. Also there is a pulsing nature of an electric fuel pump that may need suppressing.
nkaminar
Well-known member
Bob, Would an ignition condensor (capacitor) on the output side of the relay do the job? The wire out of the condensor connected to the output and the case connected to ground.
I was taught to spell the ignition capacitor "condensor" and not "condenser." Spell checkers have destroyed variability in spelling. Except for people who do not use them.
I was taught to spell the ignition capacitor "condensor" and not "condenser." Spell checkers have destroyed variability in spelling. Except for people who do not use them.
The Master Cylinder
Well-known member
Such as???
Well, I have a solid state 6V+ to 12V- converter (or is that convertor?) in my car. And I have a CB going through a cigarette lighter. Neither of which are stock, I acknowledge, but do add to the touring capability of the car.
Y-Blockhead
Well-known member
Haha, I like it! Cafe Press (and I am sure others) can make a magnetic sign for you. Years ago, I drew up and I had made the one pictured below for the back of my Town Sedan. It is still on my RR fender.
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Y-Blockhead
Well-known member
I have a Garmin GPS and a electronic Tach and neither is bothered by the relay or noisy ignition.
rotorwrench
Well-known member
Relays can use diodes or varistors to suppress back voltage. As long as the fuel pump is on a common electrical buss, there should be no need for RF suppression for it. I assume the system is maintained by an alternator. The old 3-brush generators won't keep up.
The original model A ignition system switch controlled the coil ground side. Changing over to control the power side is the best way to change to a power buss system so that accessories can be used. The ground side of the coil should always be isolated by itself. The power side should be interconnected to the battery through the ammeter unless a person wants to trade it for a generator/alternator out warning light.
The original model A ignition system switch controlled the coil ground side. Changing over to control the power side is the best way to change to a power buss system so that accessories can be used. The ground side of the coil should always be isolated by itself. The power side should be interconnected to the battery through the ammeter unless a person wants to trade it for a generator/alternator out warning light.
Y-Blockhead
Well-known member
Thank you.
I would suggest to keep it simple. I once thought it would be neat to have the "Idiot Light" in my '55 Ford Ranchwagon work off the Alternator. First time I started it, it wouldn't shut off because the alternator was back feeding the ignition thru the "Idiot Light". Made me feel like an idiot, haha. I had to add a rather large diode in the system to get it to work.
rotorwrench
Well-known member
Yes, the generator cars ran the Gen light through the voltage regulator so it has to be set up like a newer alternator car system. The GM 10si can use the two spade terminals to connect an Alt light.
updraught
Well-known member
You might want to check your float to see if it has a "g" on it for gravity? I think all the S carbs were gravity.
D, thanks. So since with this there are essentially two power circuits (one through the key, one through the relay) where does the ammeter go?John, I think I would re-wire your ignition switch so it is before the coil. This eliminates any possible issues with the ignition circuit. Depending on the current draw of your electric fuel pump, you could then add a relay. Adding a relay will also reduce current flow thru your switch. Not shown in my drawing, I have a fuse in the large red wire going to the relay.
This is the way my switch is wired, minus the relay, to power my Tach. A little more complicated then original, but that is what we get when we start modifying these old girls...
Hope this helps.
