+12v with key on

[Baker7888]

Hey guys I have my fuel pump, water pump and fans all wired thru separate relays, and they are all fuse protected between the relay and battery.

I need a source for +12v with key on for all of these (from relay) and am wondering if I can splice these together into one wire for cleanliness. Was thinking about determining a source off of the under dash fuse block and adding a fuse. ((Would be much cleaner than “finding a switched 12v source and tapping into it”))

Thoughts??

 

[Built6spdMCSS]

How do you have them setup to come on? What energizes the relay, a manual switch for each?

 

[Baker7888]

How do you have them setup to come on? What energizes the relay, a manual switch for each?

The fuel pump is switched on by oil pressure switch which also gets signal from starter circuit during cranking

The water pump switch will be direct 12v when key on

The fans switched on by temp switch

 

[mikester]

Take a test light and check the bulkhead connection. I just had to do this for a key on hot for a transmission kickdown switch. I would have had it hooked up yesterday but I didnt have an extra Packard 56 terminal. I ordered them from American Auto Wire this morning. Hoping they will be here in a couple of days.

 

[Built6spdMCSS]

So you're wanting a 12v key on wire just to trigger the relay, nothing under any load

 

[Baker7888]

So you're wanting a 12v key on wire just to trigger the relay, nothing under any load

Im not an expert with electronics (bear with me) I followed wiring instructions for each kit. The only one that makes any mention of wire size for 12v-key-on is the fuel pump kit, which is only 16 gauge from the oil pressure switch (not relay) (the relay has 12ga going to the pump)

The other relays (one for WP and one each for fans) all need a 12v-key-on but dont mention wire size. So to answer your post, yes i think it’s just to trigger the relay (or switch for FP)

I think there are some spade connector accessory taps on the under dash fuse panel. I need to install my battery so i can test…. Thinking i can just splice my 4 - 16ga trigger wires into say a 10- or 12ga wire that goes to fuse panel. Not sure if this is correct but also dont see why they’d need to be separated

 

[Built6spdMCSS]

Your thought is good, terminal 86 is the 12v trigger, it pulls barely any amps so you could have a large 12ga spliced to feed all of them.

30 is your load in, 87 is the load out. That's your fused battery power, 12ga or bigger wires. Make sure grounds are good for everything.

 

[Baker7888]

Your thought is good, terminal 86 is the 12v trigger, it pulls barely any amps so you could have a large 12ga spliced to feed all of them.

30 is your load in, 87 is the load out. That's your fused battery power, 12ga or bigger wires. Make sure grounds are good for everything.

Okay I will run a 12ga wire from fuse panel (12v-key-on) thru grommet in firewall, then splice my trigger wires (16ga) to the one 12ga wire.

I thought about using an add-a-fuse for the fuse block side. Is it nescessary to fuse this wire and if so what would be a good size? — I gotta check with a battery and test light to see if they are switched but i thought i saw a couple accessory slots on the fuse block - single spade terminal connection. Would it be ok to use this connection with no fuse since i am fuse protected on the battery side of the relay?

 

[Built6spdMCSS]

Coming out of the fuse Box it's going to be fused already, that circuit if it's going to the 86 terminal on the relay is not going to have a lot of load so 10A at the most.

Here's the thing to think about, if you blow that fuse you lose everything.

 

[Baker7888]

Here's the thing to think about, if you blow that fuse you lose everything.

Is there another option? Tapping into without fuse?