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Sorry if this is a noob question, but Im new at working with wires in the car.   I am in the process of rewiring my 71 240z (painless wiring) and learning as I go.  Im trying to add relays, so Ive made a box of 6 relays and wiring's...

My question is:

Since the relays will be near the main fuse box...can I source all of my relay connections from the main box or do i have to rewire the current setup?   ex.  Fuel pump....can i use the main fuse box for the pump and add a wire to connect it to the relay panel..or do i i have to take the actual wire to the fuel pump and redirect them to the relay panel?


Sorry if this is a stupid question but this is my first time trying to wire a car

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Did your Painless harness not come with a fuse box?  Or maybe it did, but you're wanting to retain the originality of your stock fuse box?


If I understand your question correctly, you're asking "what's the best way to source 12V + for each of my relays?".  Is that correct?


If so, then you can really use any hot source available.  If your stock fuse box is in good condition, then there's no reason why you couldn't use the lead for the fuel pump from the fuse box (using your example).  That has the added advantage of keeping some semblance of the original circuitry should you need to trouble-shoot an electrical issue sometime down the road. 


Regarding the stock fuse box....if you haven't already done so, I would recommend going through it to ensure all leads, connections, and solders are in good shape.  Resolder any leads that may look questionable.  Clean up all contact areas with fine-grit emery paper.  MSA offers some nice upgraded fuse boxes that you may want to consider:  https://www.thezstore.com/page/TZS/CTGY/classic10a03 .  

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Sorry if I didnt explain myself clearly...still learning...

The painless wiring came with a fuse box that I am going to use (the original wires and box all fried up).  I think the confusion is that the relay panel also has fuses and Im calling it a fuse box.  (Also the relays I have,  has a built in fuse)  Ill just call it a relay panel.  So based on your reply it sounds like i can connect all my relays directly from the fuse box and not have rewire everything again.  I can just add a wire to the back of the fuse box and jump it to the relay.




Wiring is driving me bonkers and I dont want to burn the wires again, so I want to add relays as much as i can.

Of the 6 relays, are there any "ABSOLUTELY" must have?   I was going to use them for: 

1) fuel pump

2) low beam

3) High Beam

4) horn





thanks again!



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Relays are a good idea on any high-load circuit.....which of course will vary from car to car.  High output stereos/amps are a good example.  At a minimum, I would suggest considering adding your running lights and starter to your list of relay circuits.  If you have a manually-controlled electric fan, that's another good candidate for a relay, as well as the blower fan for your heating/ventilation system.


You can add as many relays as you want to your harness, so don't artificially limit yourself to six.

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Thanks for that.   Ive started setting up the relays but now have a new issue.


My car cranks , and then starts and then immediately dies.   I believe its the fuel not getting into the carb (SBC).   When i manually press the gas i can see the gas squirting  out from both barrells.  I changed the fuel pump, filter, changed the oil sender unit, new HEI ignition, double checked the firing order...what else is left?   i replaced the fuel regulator about 8 months ago...do you think it could be the cause?   Since it fires up and starts, It must be getting spark and ignition. 

ANy help is greatly appreciated.  

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2 hours ago, captainkim said:

I originally had cap, rotor and replaced the ignition and it still had the same result.  I thought if I changed to hei, that would do the trick...but it’s the same result.  I’ll check the wires. Is there a way to test the module?

I just saw it was a common cause, when looking at sbc forums.  So I do not know the process of checking the module.  What fuel pump are you using?  Is it in the stock location or a mechanical run on the engine?  If using a Datsun electrical fuel pump, that is way too much pressure for carburetors.


You stated you have a 1971 Datsun 240Z.  But looking at past post and threads, the engine is a SBC with a T56 tranny.  It is very hard for us to help, when complete information of the vehicle is not relayed in the 1st post, as not every knows of other threads stating what your car actually has under the hood and inside the vehicle.


So lets basically start fresh


  • 1971 Datsun 240Z
  • Small block Chevy engine with a T56 transmission
  • Painless wiring 21 circuit harness with GM 10101 harness


So the vehicle ran correctly, up until the wiring fired and melted?  Is the alternator an internal or external regulated alternator?  Did you install a voltage regulator into the system, when an internally regulated alternator is installed?  I see from the Painless thread you started, asking about a voltage regulator.  What is the amperage of the alternator, being that it may be more than what the wiring harness can handle?


You also stated something about relays.  You have a horn relay that is attached to the fuse panel, as it is part of the Painless kit you bought.


Did you go thru any original Datsun electrical components or removed them before installing the Painless kit?  You don't need a ballast resistor for an HEI, as the coils have different internal resistance.  Same with the voltage regulator found on the early Datsuns, if the alternator for the SBC is an internally regulated.


When it does run for a few seconds, is it smooth or popping before it dies?  You may have the distributor in 180 degrees.  I don't know it is keyed for only one install or if can be put in improperly.


Sorry for a long post.  So please provide us with all the information we need to help you.  And don't stress out, step away for a few minutes and then get back at it.  I know, from working on wiring and much more when I worked for Land Rover and Jaguar.  Pictures could do even more help than words.  Like we need to know if the painless kit goes all the way to the components or just spliced in.

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Thanks for the encouragement.  OK   so this is an early 71 240z.   It has a SBC with a T56 transmission.   After driving a bit, the wires started smoking and found some burned wires.  Instead of tracing each wire, I ripped out all of the harnesses (front and rear) and purchased Painless 10101 wiring.   The wiring goes all the way to the  (lights, etc) and for the ignition, I still have the connecting wires and joining it with the painless wires.The painless does come with a horn relay and i have a relay panel ready to go ion once i get this car started.  As of  now, the lights work and the ignition  cranks, STARTS...and then immediately dies (i tried giving gas b4 dying but it didnt work). 

Ended up buying and replacing:

1) Ignition Coil

2) Just to be sure I got rid of the old ignition and bought an HEI 

3) Carb is new and I was able to drive prior to wire issue

4) Fuel Regulator

5) Oil pressure sender

6) Starter

7) Fuel Filter

same results


I have a single wire alternator and from other members, I was told i didnt need a voltage regulator.  I havent setup the relays yet.  Want to start the car  before tidying up the wires.

When I turn the key to the ON position, I can hear the fuel pump.   On the carburetor, there is no choke and when i give it gas i can see the gas coming out from both sides.  It starts REALLY SMOOTH and easy but dies right after as if its not getting gas at idle.  I rechecked the firing order, re timed with the distributor.  Im thinking its the fule not getting in at idle.  Would i be able to see the gas coming out into the carb when the car is at idle?


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So it seems you have a handle of the electrical, for the most part.  And it pretty much comes down to the vehicle not staying on and dieing.


So the carb is new and was on the engine before you had your electrical issue?  If put on after, most carbs are sort of tuned to allow for decent starting, but many still need to be tuned to allow for the best operation.  Can't tell you if you can see fuel, as don't know what type of carb you have, with some having chock plates covering the fuel nozzles. Same goes with the regulator, carbs need only a few psi to work, with their regulators usually in the 4-9 psi range.  Fuel injected use regulators that can handle the 30-40 psi needed.


Do you have a container, that you could see if the fuel pump cuts off after 5 seconds?  Remove the fuel inlet to the carb and put in container.  Have someone else crank the vehicle while you hold the container.  If shuts off at about the same amount of time as your vehicle did, then that points to the fuel pump relay or fuel pump.  If keeps putting out a good stream, then it may be your carb is not tuned correctly.


Is you HEI part of the distributor or a separate part, that is wired in connection to the distributor and coil?  If part of the distributor, that has a coil in the cap and no need for another coil. 


If you could provide pictures and even better video of you trying to start your vehicle, that would be best.

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I think I found the culprit.   After I changed the fuel regulator, I must’ve loosened the fuel pipe even more than it was before.   It must’ve been a slow drip and now it puddles on the floor.  I was able to find the leak BUT the pipe / attaching connectors are loose and they are right above the tranny and I have no way of reaching it to tighten unless I pull off the tranny (which I don’t know how to do).  Is there some magic glue or tape that can be used for those impossible places to reach?  It’s dripping at the brass connectors and not on the pipe ...as far as I can tell.  This is frustrating that I can see the problem but can’t do anything about it. Unless I cut the area right above the spot from inside the car .....and then what?  More work.


do you know if there’s some specific way to get to this?   I don’t know if this is a modified fuel pipe or stock so I apologize in advance if I lost you. I tried to upload pictures and reduced the size and it just keeps giving me error 


gonna sleep on it 



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If I'm reading your most recent post correctly, you're saying that your fuel line ("fuel pipe") runs inside the tranny tunnel (above the transmission) and there is a connection fitting somewhere in there that's leaking but you can't reach it due to it's location above the transmission.  If that's the case, you have a couple of options...


You can access that area (from above) via the hole in the tranny tunnel where your shifter is located.  I don't know how much room you need to access the fuel line fitting, but that may help.  Second, you can unbolt your transmission mount (and the driveshaft), loosen the engine mounts, and let the engine/tranny rock back/down which should give you more working room on the fuel line.  It sounds like a lot of work, but it's really not, and it may give you enough room without having to resort to pulling the tranny out entirely.


Obviously, you need to fix a leaking a fuel line; but whether that's the cause of your engine not running....I honestly doubt it.  It would have to be a HUGE leak to prohibit your engine from at least idling once started.  It does sounds like a fuel issue, but probably something other than this one leaking line in the trans tunnel.  Sorry to be the bearer of bad news, but good luck with the fixes.



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Hmmmm....that looks pretty sketchy (for at least a couple of reasons!).  I'm assuming that's from a PO; and it's probably already on your long-term "To do list" for full replacement and rerouting.


Looks like a mounting tab or piece of the casting on the transmission was cut away to make room for the fuel line?  That's definitely a high-probability area for damage to the fuel line....lots of vibration and movement on the drivetrain, which can obviously translate into rubbing on the fuel line.  If you're not planning to replace and reroute the line anytime soon, you may want to try completely cutting that tab off now.  A small angle grinder may be able to get into that space and do the job.


On the plus side, your engine compartment looks quite clean and tidy!!  :-)

Edited by jhm
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Thanks!!!  I tried both suggestions but the shifter was too far out and I really tried to take out the driveshaft etc but without a lift my arm went dead and is impossible for me to tackle.  I was debating

1) buy a new rubber fuel line and start from the rear area and reroute

2) cut a hole in the tranny and replace the broken connecters

3) I try to squeeze some in weld




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Quite honestly, the easiest (and best overall) solution might be to replace and reroute now.  That just does not look like a good location for the fuel line for several reasons.  Keeping it inside the trans tunnel is good for protecting the lines, but choose a more accessible location so you can easily repair or replace in the future.  Not sure about running rubber line for that long run from rear to front.  That's typically metal line for safety and durability purposes.  I personally prefer Cunifer (Copper-Nickel); but others prefer stainless steel, or something else.  Maybe rubber with braided stainless wrap is an option here if you are against running new metal line for whatever reason?  I'm sure others much smarter than me will pipe in with recommendations.


If you don't have previous experience fabricating brake and fuel lines, now's as good a time as any to learn.  It's actually quite easy once you've done it a couple times, and it's a skill that will pay many dividends for a long time to come.

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Listen to what @jhm is telling you, it's good advice.  No fuel line should ever be running over top of the transmission like that, there is the possibility of it being pinched, your heating the fuel up unnecessarily and there is no reason to have that connector there except to patch up a previous owners poor planning. You can go fancy with SS or just p/u a coil of fuel line at NAPA, both will be safer than what you have right now.

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