During my engine upgrade, I needed some ignition hot circuits so I used a fuse tap & ran a wire to a new fuse block (3 circuits, 70 amps total). I used the three circuits for my ECM, my cooling fan and my radio.

As I proceed to the next part of my project, I've determined that I could use 3 more circuits. My question is, can I just tap into the wire I'm using to power the first fuse box? Or do I need to find another place to put a fuse tap in & run another wire to power it?

 

You're already overtaxing the original wiring you tapped to add your fuse block. OEM wiring was bare minimum to run what was initially on the circuit to begin with... let alone, add more to it.

 

70 amps is a pretty major load, needs 4ga feeding it, possibly more, a fuse tap is not the answer. Run a cable from the battery to your buss bar/fuse block. If it needs to be ignition switched install a solenoid to switch it. 70A in addition to whatever the car normally draws will probably leave little to no reserve capacity from the alternator, at low rpm it probably won't keep up, upgrade it or expect to replace alternators and batteries regularly. If you upgrade the alternator you will also need to upgrade the alt cable(s) to carry the higher load.

 

Wow - I apologize, I could not have described my setup any worse than I did...that's what I get for quickly trying to post before going to bed. Let me start over...

I purchased a 3-circuit, 70 amp ignition-on junction box. This came with a 70 amp SPST relay. The relay is powered by a wire that goes directly to the battery, the wire from the fuse box (the one I tapped) is an ignition-on wire that solely turns the relay on and off. Here is a link (Painless Performance) to the junction box I bought, if that helps.

My plan is to purchase an identical setup, so the new relay would also get power directly from the battery. I would like to tap into the same on/off wire to switch this second relay off and on since it, too, will be an ignition-on fuse box. I wasn't sure if I could use this same wire to turn on both relays or if I'd need to find a second ignition-on source to turn on this relay.

 

There is no way that is a 70 amp relay. Most Bosch style relays are rated at 40 amp peak, with a continuous rating of 25 amps. I have only seen lower specs on that style relay not higher.

You should get away from using fuse taps at any time, they are not reliable and some can damage the fuse box, due to spreading out the contacts.

That being said, the trigger to the relay is low current and you'll be able to trigger several relays from a single ignition source.

 

Not sure how they would or could market it as a 70 amp relay if it isn't. I suppose in the long run it doesn't matter as I'm no where close to 70 amps with the 3 circuits - I believe I have one 20-amp & two 10-amp fuses in there right now.

I agree about the fuse taps, but I wasn't sure how else to properly wire an ignition on source.

 

It probably is 70A more than painless makes them, they're OEM on some stuff, has two giant prongs and a couple smaller ones, looks similar installed but the business end is nothing like your standard 30/40A 5 prong.

Should be some specs on it, most relays take milliamps to actuate, you can run a lot of them off one wire.

Not all fuse taps are created equal, there is a style that the contact slips thru therefore it adds no thickness to the contact. They are not as reliable as good old wiring though. Myself I've always been partial to tapping the radio ign wire, or right off the ign switch, no scotchloks or t-taps, solder or a properly heatshrunk butt connector.