73 Alternator upgrade specifics with respect to fuel pump relay

[pazcarguy]

Hello, I have a 73 240 (with elec fuel pump factory installed) and purchased an MSA alternator adapter plug last year. Just getting around to installing this with a ZX alternator (internally regulated) and I have read multiple posts about the fuel pump relay being energized and draining the battery (just on the 73 with the factory fuel pump relay). After searches, I could not find any specifics of what is needed to correct battery drain. I have read that you need to wire a relay in, but again no specifics. If anyone out there has the details, It would make a great writeup (color codes on wires/pics/etc.) I would sure appreciate any info you guys have. Thanks

[SteveJ]

For safety reasons, if you wish to maintain an electric fuel pump, you should install an oil pressure switch in the circuit to energize the relay. I have another idea that incorporates other outputs from the alternator, but I haven't had time to test it.

In a purely stock configuration, the voltage regulator plugs into a 6 pin connector. The electric fuel pump modification from Nissan added a short harness that goes between the alternator and voltage regulator. Simply removing that short harness would remove the power from the fuel pump relay.

[pazcarguy]

For safety reasons, if you wish to maintain an electric fuel pump, you should install an oil pressure switch in the circuit to energize the relay. I have another idea that incorporates other outputs from the alternator, but I haven't had time to test it.

In a purely stock configuration, the voltage regulator plugs into a 6 pin connector. The electric fuel pump modification from Nissan added a short harness that goes between the alternator and voltage regulator. Simply removing that short harness would remove the power from the fuel pump relay.

Steve, I am assuming by disabling this (by removing connector), this would prevent power to the fuel pump at all times. Disabling after driving would prevent battery drain but this seem slike a hassle each time to disconnect and reconnect.

[Jarvo2]

Here's my writeup on my '72 Fuel Pump wiring and Alternator upgrade. I wired in the oil pressure switch and its worked great (just need to make sure that you have a 2phase on that allows the pump to activate when the starter is being activated). Please note that the OEM '73 fuel pump wiring will not work with the approach I took for my Alternator upgrade. You may want to reach out to Dave Irwin (famous for his headlight harnesses) to discuss the approach for the '73 fuel pump if you don't fully rewire it with the oil pressure switch.

Dave's 1972 Datsun 240z: Alternator Upgrade

Dave's 1972 Datsun 240z: Electric Fuel Pump Installation

[SteveJ]

While you wouldn't be able to just move one wire over, the 73 fuel pump wiring could be modified to use an oil pressure switch in a manner similar to what Dave did.

[SteveJ]

Steve, I am assuming by disabling this (by removing connector), this would prevent power to the fuel pump at all times. Disabling after driving would prevent battery drain but this seems like a hassle each time to disconnect and reconnect.

Correct on both accounts.

[pbarcher]

Brian,

I had the same battery drain problem when I did alternator upgrade a few years ago, which appears to be unique to the 73 model year. You may know that the electric fuel pump was added as part of a recall to alleviate vapor lock, but is not needed otherwise on a stock engine. I simply unplugged the wiring harness at the relay and my engine runs fine with the mechanical pump.

I agree with others that if you want/need to use an electric pump you should incorporate an oil pressure switch for safety. Search for posts by Dave Irwin for more on this topic.

Peter

[pazcarguy]

Thanks for the responses. My car has some mods and I need to run an electric fuel pump. I have an L28 with flat-top pistons, N42 head and a Schneider cam running tripple DCOE45's. I no longer have the mech pump but am running a high volume low pressure Carter pump that is powered from the original harness conections back near the fuel tank. This pump setup was recomended by Top End Performance from California who is a distributor of Weber products. I will search for Dave Irwin. Thanks, Brian

[SteveJ]

Do you have your internally regulated alternator already? If so, post pictures of it and any documentation that came with it.

[pazcarguy]

Hi Steve,

I have been e-mailing Dave Irwin and he shed some light on my issue an what I would like to accomplish (basically brighter lights). As my electrical system is stock and only item I have "extra" is a MSD unit (no big stereo or foglights etc.), I am going to keep the stock alternator and invest in the headlight upgrade and parking light upgrade. Thanks for your replies but at the moment I plan on pursuing this route.

Brian

[Stanley]

So you're just keeping the stock electric fuel pump wiring setup? And there's no easy way to use the stock electric pump wiring and internally regulated alternator on a '73 ? I had planned on doing the internally regulated alternator in the future, and keeping the stock electric pump. The pump would be unplugged from the wiring (since it's out of the loop now and my gauge shows the mechanical pump is providing plenty of fuel pressure), but could be quickly hooked up in case the mechanical pump ever craps out on the road.

If there's a way, the specific details would be helpful for 73 Z owners, since not everybody is good at electrical. Otherwise I guess keeping everything stock is ok.

One question - any photo of that wiring harness on the 73's that you can disconnect to cut power to the electric pump? That might be easier than crawling under the car. Have an old engine manual but it's for 72's.

[pbarcher]

No need to crawl under the car. Just unplug the relay in the passenger foot well. It will be the one that's warm when the engine is off.