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electric fuel pump power supply?

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mtlman8

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Hey guys, is it better to connect the pump to the + side of the coil or a spare terminal in the fuse block?
 
I don't know the wiring on a TR8 (yet), but I would say the coil, because you only want power with the key on, not at all times. But then if it's fused off ignition, that may be better, but in any case, a fused connection should be used.
 
:iagree:
But, doesn't a TR8 have a ballast resistor? If so, the + side of the coil won't have a steady 12v on it; and the draw of the pump may interfere with coil operation.
 
it's a tr4... I also failed to mention I have pertronix electric distributer and a high performance coil.the fuse block has only two fuses in it, one always hot and one only hot when the ignition is on.
 
OOPS!!! I was reading two different threads and ASSUMED that you were talking about a TR8. My dumb mistake and I apologize.
 
I would power it from the ignition switch, from a terminal that is "hot" in the run position. Should be next to the coil lead (generally white in her majesty's service). I think the lucas wire color standard for electric fuel pumps is green/blue....?

Some guys might suggest, when installing a pump, to have the ignition switch power a relay that then powers the coil and pump - but I generally don't.
 
Have it run thru a relay then you can use that same relay to power your 3 wire O2 sensor
 
Had to chime in on this one. I just got finished adding an electric fuel pump to my 72 GT6. I used a relay,NAPA #AR274 and a holley fuel pump safety switch. The safety switch only allows the pump to function when there is oil pressure. There are 3 contacts on the switch, C(common), NO(oil presure), and NC(gets power from starting solenoid only while key is in start). By using safety switch,pump won't run if key is in on position but engine is not running. I'll post pictures and a diagram by the middle of next week.

Jim
 
the ignition switch WHITE wire is connected to the coil... which is why I connected it there in the first place.I think I may have some issues, the previous owner had the WHITE wire spliced into a aftermarket ballest resister, and an electric fuel pump in the ENGINE BAY! so off the get go i'm not exactly sure why or where the WHITE ignition wire should go... straight to the coil? if so then isn't that the optimum place for the fuel pump?
 
I used a relay so that I could power the pump directly from the battery with an inline fuse. The safety switch powers the relay only. I did not want to have the pump in the same circuit as the coil. The NO contact on the safety switch is connected to the white wire(wire goes to coil just as in your vehicle) coming out of the igntion switch. An electric fuel pump works best as a pusher rather than a puller. Best place is as close as you can get to the fuel tank and as low as you can safely mount it
 
All of the white wires in a TR8 are switched power. All of that power runs thru the key switch. Taping into that circuit for any electrical item that draws significant current is a bad bad idea. If you don't believe me see the picture Mike (wedgeworks) just posted of all the melted white wires behind the fuse box. Only tap into the white switched power to activate a relay. Mount a relay for the fuel pump in the trunk close to the pump. Run fused constant power directly to the relay. Take that directly off the battery. Run a switched power(white) to the relay. Connect a ground if needed. Run a new switched power from the relay to the pump. That way the only current draw on the switched power circuit is the power required to pull in the relay. You can use the stock TR7/8 relays and their holders from left over wiring harnesses. Oh, and don't try to pull 12 volt switched power from the coil. You won't get 12 volts. There is a cluster of white wires crimped together up behind the fuse box. Tough to get at unless you drop the fuse box, but that is the best place to scab on another switched power wire. I like to run a wire from that crimp to the engine bay where I set up a MGB fuse block of switched power. Whenever you need another switched power, just come from the fuse block. I also like to set up another MGB fuse block as a constant power source.
 
You need to attach your fuel pump to the fuse that is key hot only! If you have a back feed (grounded wire) on the coil you could get a back feed and your car will not start or run poorly. Don't ask me how I know, but I know. Good Luck, Bill Close, Mesa, Az.
 
mtlman8 said:
the ignition switch WHITE wire is connected to the coil... which is why I connected it there in the first place.I think I may have some issues, the previous owner had the WHITE wire spliced into a aftermarket ballest resister, and an electric fuel pump in the ENGINE BAY! so off the get go i'm not exactly sure why or where the WHITE ignition wire should go... straight to the coil? if so then isn't that the optimum place for the fuel pump?
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White wire straight to the coil is fine, provided you have a coil that is designed for it. The original coil would be; but the aftermarket ballast resistor would suggest that some previous owner substituted a more-readily-available "ballast required" coil. If so, you need to either keep the ballast, or replace the coil.

Electric pump in the engine bay will generally work fine; but as noted, towards the rear of the car is a slightly better place for it.

The little Facet pumps that I like only draw about 1 amp, so there should be no concern over powering it through the ignition switch. However, a fuse would be a good idea, as the "white" circuit has none and hence is more prone to let the smoke leak out if there is a failure.

However, some other electric pumps draw substantially more current, so a relay would be a good idea for them.

In addition to the fuse, you really should have some device to stop the pump in case of an accident. There are several ways to do this; the most elegant IMO is to use a Bosch relay that senses the engine turning and disables the pump a few seconds after the engine stops turning. They are kind of expensive new, https://www.partsgeek.com/catalog/1978/volkswagen/rabbit/body_electrical/fuel_pump_relay.html , but were used on a lot of German cars with early fuel injection and so should be readily available in a junkyard. Mine cost $1 and works perfectly.
 
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