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Subject How-To: Injector Switched Power Line Using Fuse Box Tap
     
Posted by jzack on July 30, 2006 at 12:02 AM
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Message Engine Bay Circuit Expansion Using Fuse Box Tap

Recently I needed to replace a failed injector on my '91 Z. Figured as part of the repair I'd
rewire the injector's harness connector to a switched 12v source (rather than always on 12 volts).
There's some concern that with the addition of ethanol to the gasoline supplies -- damage can be
done to the injectors (from electrolysis) when the car is off, since voltage still remains applied to one of the injector's connectors. I thought it made sense to rewire my new injector to try and avoid this issue and came up with a pretty fast/easy way to tap into the engine bay fuse box. Note: In later years (‘94+) Nissan did make a wiring change over to switched power for the injectors!

Parts needed:

- 2 male spaded crimp connectors (14-18-gauge size, blue)

- 1 foot of #14 gauge stranded wire

- 10 ft of #16 or #18 gauge stranded wire

- 1 push-in (square-ATO) auto fuse holder (FYI: my local ACE hardware store had a type that self attaches to wires like t-taps. Unlike the ones carried by car stores, Radio Shack, etc – it allows longer lengths of wiring to be used)

- 1 in-line (round) fuse holder and 4-amp fuse-- a square type holder and fuse can also be used

- Misc: Barrel (crimp style) splice connectors and cold wrap electrical tape.

Details:

The idea is to tap into the A/C power circuit by relocating the 10-amp fuse. Relocating the fuse to another spot inside of the fuse box makes it easy to add an extra circuit at the fuse connection. Here's a diagram of the circuit:

Image Hosted by ImageShack.us

This mod is pretty simple -- one side of the A/C fuse is connected to the car's ignition key switch circuit. Connecting another line to the switched ignition circuit allows the injector to only be powered when the car is running. Here's how everything looks connected in the fuse box:
Image Hosted by ImageShack.us

The spaded connectors are a great fit for the A/C fuse terminals -- only thing I did was to put a small piece of cardboard between them to act as a spacer and keep the terminals from shifting around..

Here's another view:
Image Hosted by ImageShack.us


This is how things look all nice and neat before the cover install:
Image Hosted by ImageShack.us

Additional notes:

- My main goal was the easy install of a switched power source for my (1) new injector. I do have some minor concerns about the reliability of permanently using this arrangement for all 6 injectors. However, this method avoided flipping the fuse box up side down to splice into a pretty cramped nesting of wires. It's also easy to reverse the mod if changes are needed down the road. FYI: A/C circuit seemed to be a good low risk choice for experimentation. If the A/C stops working due to a loose wire, no big deal!

- Wanted to experiment with this circuit arrangement. I'm pulling the plenum next winter and replacing all the remaining injectors, that's when I’ll rewire all of them to a switched 12v-power source. I wanted to make sure this configuration didn't cause unwanted noise on my stereo system or any other issues, so far it's been fine. I'm pretty sure another injector is on its way south - will use this power supply connection for that repair as well.

- The injectors pull around 1.1 amps of current. Nissan OEM wiring looks to be 20 gauge in size. I decided to use 16-gauge wiring and a 4-amp safety fuse. This would seem to be well above the circuit draw down requirements. Note: The extra 4-amp fuse is a important safety feature – DO NOT omit it!

- Splicing the newly added +12v switched line into the injector’s harness was easy to do too! Make sure the battery’s ground is disconnected before proceeding: Strip the harness cable’s outer sheathing and then cut the always on white/black +12v line about 4 inches from the connector’s dust boot.. Splice the new switched 12v line into the white/black 4 inch line running to the connector using barrel type male/female crimp terminals. Wrapped everything back up with some cold wrap electrical tape.

- FYI: Here's a handy web page I found for wire gauge sizes: CLICK HERE >>>
La-Z-Link


DISCLAIMERS…

READ AND FOLLOW ALL SAFETY PROCEDURES RECOMMENDED IN THE
NISSAN SERVICE MANUAL FOR WORK ON THE 300ZX Z32 ENGINE. MAKE SURE THE CAR’S ENGINE IS COLD TO AVOID BURNS AND DISCONNECT THE BATTERY BEFORE STARTING ANY WORK. ALWAYS TAKE PROPER SAFETY PRECAUTIONS AND USE COMMON SENSE WHEN WORKING ON THE ENGINE AND ELECTRICAL SYSTEM.

YOU ARE RESPONSIBLE FOR YOUR OWN SAFETY WHEN WORKING
ON YOUR CAR. THIS WRITE-UP IS AN EXAMPLE OF ONE WAY TO PERFORM THIS MAINTENANCE, IT MAY NOT BE THE SAFEST OR BEST WAY TO DO IT. YOU ARE RESPONSIBLE FOR DETERMINING HOW THESE REPAIRS SHOULD BE EXECUTED IN A SAFE AND CAUTIOUS MANNER -- AUTHOR IS NOT RESPONSIBLE FOR ANY HARM TO YOU, YOUR CAR, FUTURE GENERATIONS, YOUR PROPERTY OR TO OTHERS WHILE OR AFTER PEFORMING THIS OR ANY OTHER AUTOMOBILE SERVICING...
.

     
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