I am installing a Retrotek EFI setup on my car. I spoke to mark at MAD electric and he said to wire up my in tank fuel pump thru a relay and a oil pressure swicth so I bought everything from him. The retrotek wiring harness has a lead labled positive fuel pump. I called Retrotek and they said I should only feed the pump with there one wire and not to use the relay and oil pressure swicth. There lead is a small wire probaly a 14gauge wire. Mark said to use at least a 10 gauge wire to feed the pump. So now I dont know what to do or how to wire the fuel pump with the relay and the positive lead from the harness. Retrotek also said that the relay was built into there computer. Not so sure I beleave that. Any help would be greatly appreciated. Thanks.

Hopefully someone knows a bit about the Retrotek EFI setup you're using and can verify if it has a relay inside or not. A relay is needed, although the computer may already have it. There typically isn't a problem with having one relay feed another, unless the computer is doing some funky current sensing on the pump motor. If the relay inside the computer is not changable, that might be something to consider. Relays do fail, especially with inductive loads like a pump motor. Having one external to the computer might be a good thing.

14 gauge wire seems kinda small for a fuel pump. Wire has resistance per linear foot. So when you're gauging wire, you have to consider the length and bump up a size or two for the long runs.

I don't know anything about Retrotek, but it's not uncommon for a flunky to run the phones who is looking at a product spec sheet.

As far as I know, GM started using oil pressure switches on their fuel pumps. The idea behind it is that when you crank the engine, the starter solenoid wire energizes the pump to get fuel flowing, but once the engine is running, an oil pressure switch takes over and keeps the fuel pump relay turned on. The reasoning behind this is that if your engine ever looses oil pressure, the pump cuts off and hopefully saves the motor from a painful death. What I'm not certain of is if there is any magic going on inside the GM engine controller. Oil pressure doesn't build instantly, and the ECM may be hanging on to the fuel pump relay for a second or so after the engine starts to allow time for the oil pressure to come up. You might have to study some of other's setups to determine what is right for you.

I don't know any thing about retretec, I put an edelbrock kit on mine. It had the relay
fuse and all. I dont know, but the fuel pump needs a relay. and fuse before relay. Remember. this IS gas, My system has a fuel pump shut down if engine is not running, \
simular to factory. How is your system controled?

I would take Mark's input anyday over others :thumbsup:
He has years of experience wiring vehicles and will only sell you a system/part if he knows it will work for you - and he is there to back up his stuff if needed.

As mentioned above, wire has a given resistance per foot depending on size.
The smaller the wire size the more resistance it has and the more it restricts the final voltage available to the device (your pump in this case).
14AWG wire has @2.5ohm's-per-ft
10AWG wire has @.8ohm's-per-ft
So, if you do the math ;)
You are feeding the pump (guessing it's @20 amp load max, many are around there) with 12vdc and the length of the feed is @12ft, then the final voltage available at the pump would be less than 10vdc if you use 14AWG wire - however it would be @11vdc if you use 10AWG...
so a 14 gives you a 2.5% voltage loss vs 10 which gives you less than 5% loss - I think you can see why going to a slightly larger wire pays off quite often.
I'm pretty sure Mark already fiqured this out for you.

Fear and common sense should tell you a Fuel Cut-off system is the only way to go :yes:
If there is no oil pressure closing the contacts on the pressure switch he sold you, there can be no power to the system and fuel can't be continually being pumped to your non-running engine.
In an accident or roll-over with just an On/Off switch there is no way to be assured that you, or someone, will be able to turn off the switch so fuel will still be being pumped - maybe into a area you don't want it be :eek:

All modern cars have a pressure interlock switch or an inertia switch that cuts power to the relay if the car is in an accident or rollover - it's part of the ECM/PCM.

GM stopped using oil pressure sitches several years ago, pump runs on key on 2-3 sec
and crank and with crank-cam sensor signal.

Nice detail John, but...

Those itty bitty pumps used in efi systems don't draw a whole lot of current. I used 14 gauge wire with a relay for mine, it works fine.

As for the need for a relay, I'd use one, if...

The ECU is NOT using a variable output to control the pump speed based on demand. A relay would completely defeat this.
Read the fine print on the retrotek very carefully. Talk to Fred, he has one. I think a couple other members might too. Do a search here in EFI, there is lots of info on one or more retrotek installations.

All else fails, don't second guess the instructions that came in the box.

I installed a Retrotek on my 69 last spring. I have the pump in tank. Wired directly to the Retrotek computer wire given in the kit. No relay needed . it is in the computer. You turn the key and you hear the click and the pump comes on. BTW. I also installed the regulator one foot away from the fuel pump under the back tires and looped it back in the trunk. Works great, no problems. Check out the pics in my gallery link below. It shows you the entire Retrotek install in pics. I have changed a few things since then but you will get the idea. Now I am moving the main battery back to the trunk.
Good luck.

Thank you everbody for the great responses. I have learned that the Retrotek system uses the tach signal to shut the pump off. I spoke to Mark again last night and he feels that I should use there pump + wire to a seperate relay as not to depend soley on the relay built into the computer. External relay is much cheaper to replace then computer if the internal relay fails. So thatis what I will do. One last question for everbody would you still use a oil pressure swicth or just rely on the tach signal to shut the pump off if something happens? Thanks.

Something to consider is that if the Retrotek has key-on power to the fuel pump at all times (no delay and/or engine speed sensor) would be to use a Ford fuel pump inertial safety switch. They are installed in tons of 80-early 90's Fords in the aft secton of the car, usually in the LH aft. In case of an accident the inertial switch will immediately cut power to the pump, but can be easily reset by pushing a button.

Even though the ECM in my car will cut fuel pump relay power based on engine speed I still put on on just in case the car continues to idle after a collision. Fuel fires scare the heck out of me.

...
14AWG wire has @2.5ohm's-per-ft
10AWG wire has @.8ohm's-per-ft
...

I suspect these figures are 2.5 ohms per 1000' and 0.8 ohms per 1000' respectively. A 10' run of 14 ga will have 0.0025 ohms of resistance. At 10amps you'll have a 0.025 volt drop. I suppose that's negligable. The power disapated would be 0.0625 watts distributed along the 10'. That too seems pretty small. Although I haven't measured the current draw on a high pressure EFI pump, I'd suspect it's much less than 10amps.

I change my vote - 14ga should work fine.

Vintages observations are always worth considering when doing any type of wiring. When you start getting up into tens of amps and above, a few tenths or hundreths of an ohm can lead to a meltdown or non-functioning circuit. I think you're safe in this case with 14 ga.

See what I get for typing so fast :o
I didn't know the newer pumps were so effecient, the older ones I've used drew a bit of current.
I've done more of these system for marine use than cars.
You are right, the resistance given would be for longer lengths than he will ever need...
I would still go with 'Mad' Mike's recommendations for a shut off, unless the as delivered system has some other provision ot do this. - I am also deathly affraid of fuel being continued to be pumped after an accident or shut-down - been-there-done-that :eek: (where's that little guy going up in flames smiley when I need him)

btw - the pump reset button on my "Exploder" is in the passenger side dash area. but there is also a relay in the rear LH panel - along with the interior light control system :confused: wierdest wired vehicle I've ever dealt with...

My holley system suggests a relay. The pump is turned on for a (user programable) prime time, and is turned on and kept on by the tach signal.

I had looked into an oil pressure switch, but that gets complicated... You still have to prime the system (while there is no oil pressure) and that's some tricky wiring and multiple relays... the tach signal is enough.

Thanks for everbodys help. I am going to keep working on the wiring tonight. Thanks!!!