So getting constant 12v is obviously easy. Go right to the battery. I've actually done this enough to where I just wired in a properly fused junction box. Looks clean, and not like the positive terminal is a Griswold Christmas tree!!! LOL ...but haven't had to do it much on switched power. Most of the time I was replacing something existing, and I just used the factory wiring. I've got a few new things, engine management, fan control, etc. etc. and I need a few switched 12v sources. Short of hacking into the stereo wire, or something like that, what is the "proper" place to source 12w switched power???

 

An unused terminal on the fuse box is a good place.Unless your dealing with hi amperage, then youll want to use the switch source to energize the lo side of the relay.

 

This makes for a clean install.

 

There's a whole terminal block devoted to that; left kick panel, kinda above the parking brake cable release. Has about 12 terminals, most of which are battery but some number are accessory. Power accessories like PW, PM, PS, PDL, etc. get their power from there. Perfect place... just use what the factory already put there.

 

IIRC, there are two unused accessory terminals in the block.

JamesC

 

Agreed. If it is more then one accessory or a power hungry accessory just add in a small wire to energize a relay and pull power from the battery. I think it's debatable whether or not the factory harness runs big enough wires for what is already powering, the power windows are a good example.

 

A lot of the "big enough" question about depends on whether the load is intermittent (PW, PS) or continuous (stereo, fog lights). A raw current reading is a good place to start but doesn't tell the whole story.

 

Fusebox.

The early cars ( 82-88 ? ) used the "junction block" described by others above, but that junction block doesn't exist on the later cars. When factory installed; the junction block got full time and switched power from the back of the fuse-box...... I would get the fuse-box schematic for your specific year and use it find a spare full time and switched power ports and 'custom' install an early Junction block in your ride. I don't have the 89 schematic, but this is from the 91 and yours *MIGHT* be similar.






My 84's junction block was almost full from the factory and I quickly filled it with add-on stuff. I was forced to add an additional 2 fuses to my box even when it was still a carb car (1 full time and 1 switched ). Adding a Junction block will add 6 full time and 6 switched ports and that should be enough to keep you busy for awhile !!

 

Looking for answers as well. Im looking to run multiple ign sources (gauges, cig lighter, usb, other future items) I have a nice fuse block with 12 circuits. Im not good with amps and all that crap so heres the plan.

Run a 10 gauge wire from the battery to a relay and then to the block. Use an empty ign from the stock fuse block to trigger the new fuse block relay. What amp relay would I need? 30 amp fuses would be the biggest I would run within the block.

 

This is what I just read:

The early junction block was fed power thru 2 wires leading from the fusebox. The fusebox power sources each flowed from the box thru a 35 amp circuit breaker. Full time power then uses a 10 gauge ( mm = 5.0 ) and the switched uses a 12 gauge wire ( metric = 3.0 ) to the Junction block. The junction block then had 5 "out" ports. ( 'out' wires were sized based on each accessories needs )

10 gauge appears to be the largest gauge wire in the whole car - aside from the Battery Cables. I'm no pro electrician, but I'm thinking you would be fine using 10 gauge to feed your add on fuse-box. Just be sure to use a relay for any individual accessories that require it.

 

I need a way to trigger the fuse block with ign power. I was thinking using a relay and using a wire from the stock fuse block would work.

I dont know what size relay to use however

 

I'm not sure how to help you,.....

The Ignition key IS the trigger for switched power to the fuse block. From there the switched power runs thru a 35 amp circuit breaker and out to the junction block. If every electrical devise on that switched power circuit is running and the load is too great,... the circuit breaker will trip and the circuits will be protected.

Once you wire extra accessories to the add-on junction block,....... just add a relay with each/any accessory that needs it. This is how the factory did it with the power antenna, electric fuel pump, fog lights and so on. As a matter of fact - all those accessories all use the same relay. It's also how I wire add on stuff like an electric water pump, electric fans, BOSE amps, and so on. Some stuff you will not need a relay for, such as aftermarket gauges or extra lighting.

P.S. You will want the original - or extra - cigarette lighter sockets on Full Time power !


Hope this helps !

 

For want it's worth, there are connectors designed and keyed to fit the specifically shaped slots in the main fuse block. One style each for BAT, IGN and gauge lights. Pico is one manufacturer of these. It makes it a "plug amd play" feal.

 

Yup,

If you get into a tight spot and have a terminal that is made for one socket ( Black plug / BAT terminal ) but need it to fit in another socket ( White plug / IGN terminal ) I've used wire snips to cut off the plastic "guide" on the plug so they will fit into what-ever fuse-box port I need. The locking tab will still be fine and will hold the plug in the port.

I also seem to remember a couple of these plugs that had a "daisy chain" for 2 external connections to a single fuse-box port as well. I think It was used in the early cars for radio + Power Antenna power.

 

The Pico 955-BP (power) and 958-BP (IGN) connectors have a .250" male tab to accept a crimp on female disconnect for the "daisy chain" you've mentioned.
Now my question is, what is the overcurrent protection for those ports in the fuse block? Is it only the fusible link that's upstream? I use an in-line. fuse regardless .