Hello all!

I am currently in the process of rewiring my 1970 240Z with a 21 circuit EZ-Wire kit. To be quite frank, I don't have a ton of experience in these type of things, but after looking at the original wiring diagram I'm just a bit confused. My question is stupidly simple: Am I supposed to my rewiring using the original factory diagram adapting the universal kit as I go, or am I supposed to be going based off of the diagrams included with the kit? 

I'm no electrical maven but it would seem that if you follow the Nissan diagram, you'll be incorporating some of the serious design flaws such as running high amperage power for lights and turnsignals thru the fuse box and combo switches.  Many of us have cured those particular evils with aftermarket relay kits but there are still more weaknesses in the OE layout.  You're moving from a 10 fuse setup to 21, it seems to make more sense to follow the guide of your new kit.  Good luck with the project.

It depends upon what you're trying to do.

If there were only someone who lived not that far away from you who understands S30 wiring...

Thanks for the replies. Yeah I sort of had an epiphany yesterday starring at these damn diagrams. A classic case of making things harder than they have to be I'd say. 

There was a hint in my first reply if you look again...

There is a bit of advice I can give that might help you decide on the best way forward.

If your current wiring is in such bad shape that most connections are corroded and wiring cracked, and terminal ends are beyond repair, switches are all malfunctioning, then it might be wise to start with a fresher wiring harness, switches, and new lighting/devices. If problems are only in certain areas, then address those areas. 

Why? In order to add a completely new and different wiring harness into your car, you will have to learn every wire, switch and connection of the existing system in order to adapt in the new wiring. This assumes you aren't replacing every switch, light fixture, flasher, gauge, etc. You have a ton of stock switches and gauges and such that you have to connect to, that may not be designed with the same switch logic that the new harness is built for. 

 Why not just fix what you learn is wrong as you go? Especially if you're not comfortable with electrical functions and repair. 

Depends entirely on your time available and dedication to quality connections and splices along the way. I have no doubt you CAN do it, but will the effort and final result be better than a careful review and targeted repair to the existing wiring given your time and willingness to learn and do it right? Your decision of course. 

@DoomGazey

SteveJ was offering to come help you. He lives not far from Atlanta and he knows electrical!

does anyone know worst case how much it costs to update the electrical wire harness in a 1974 260z professionally 

4 hours ago, jay plotkin said:

does anyone know worst case how much it costs to update the electrical wire harness in a 1974 260z professionally 

Are you talking about the entire wiring harness for the car or a few modern updates like the fuse block, electronic flashers, headlight and alternator upgrades?

Thanks for responding

I am looking at purchasing a 260z that currently has the following gremlins:

The following are Non Functioning; a/c,, no heat but blower works, rear defrosted, former owner removed radio which I can't imagine is a good sign.Headlights come on but not regularly. So I was told it is probably due to 40 yr old wiring gone bad. So I didn't think a professional restorer would only repair whats not working but recommend a complete rewire.. So before I buy I wanted to know what I would be looking at cost wise. Any ideas?

9 hours ago, jay plotkin said:

Thanks for responding

I am looking at purchasing a 260z that currently has the following gremlins:

The following are Non Functioning; a/c,, no heat but blower works, rear defrosted, former owner removed radio which I can't imagine is a good sign.Headlights come on but not regularly. So I was told it is probably due to 40 yr old wiring gone bad. So I didn't think a professional restorer would only repair whats not working but recommend a complete rewire.. So before I buy I wanted to know what I would be looking at cost wise. Any ideas?

There are plenty of 40 yr old wiring harnesses working just fine. If it were mine I would try to repair what you have or source a better harness if the one in the car is all hacked up. It's a time intensive project to rewire a car and that makes it expensive

10 hours ago, jay plotkin said:

Thanks for responding

I am looking at purchasing a 260z that currently has the following gremlins:

The following are Non Functioning; a/c,, no heat but blower works, rear defrosted, former owner removed radio which I can't imagine is a good sign.Headlights come on but not regularly. So I was told it is probably due to 40 yr old wiring gone bad. So I didn't think a professional restorer would only repair whats not working but recommend a complete rewire.. So before I buy I wanted to know what I would be looking at cost wise. Any ideas?

I would be willing to bet most of those problems are bad grounds or corroded connectors which are pretty easy to fix.  The no heat could be as simple as a bent push cable, it is a common problem.  Of course if you haven't laid any money down yet, having to "replace the entire wiring harness" is a pretty good bargaining chip

The wiring harnesses on these cars are not hard to access, if you go through every connector and ground one at a time with a can of Deoxit and a fine wire brush which is only a afternoons work I think you'll find most your gremlins would disappear.  But the headlight circuit is one that really benefits from an upgrade kit, easy to install and not expensive.  I wouldn't pass up an otherwise sound Z car for a few electrical faults.