switched 12v under the dash (where)

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boostedSVT

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Apr 10, 2004

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Fullerton Ca

Aug 13, 2011

#1

• Aug 13, 2011

• #1

ok guys i have searched for about a half an hour and have not really found anything about this. I have a 1994 mustang and have 5 guages and when I looked under the dash they were all getting switched 12v from the fuse box. I am sure that is not the best way to connect. I was thinking about running a wire from under the hood but need to find a good switched 12 volt. Is there a thick switched 12v under the das that is easy to hook onto or is there a better source under my dash that is easy to access.

I am running 5 guages and a boost controller so I really just need a good source for the switched 12v

easy question i know

 

BlackVert

15 Year Member

Oct 3, 2003

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Bethesda, MD

Aug 14, 2011

#2

• Aug 14, 2011

• #2

how much current do you need? there is a wire the feeds the radio that is switched. i can look it up tomorrow if you want.

if you need more than an amp or 2, i would recommend using that to trigger a relay that feeds the power you need. of course, that would mean pulling a wire from the engine bay, which is what it sounds like you are hoping to avoid ...

 

B

boostedSVT

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Apr 10, 2004

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Fullerton Ca

Aug 14, 2011

#3

• Aug 14, 2011

• #3

wells lets see.
1 vac boost gauge w/ light
1 water temp gauge with electrical and light
1 a/f gauge with electrical and light
1 fuel pressure gauge electrical with light
1 boost controller profec b spec ll
1 electrical exhaust cut out

all of them are low amp but to put it into prospective the exhaust cut out alone has a 3 amp fuse in it.

I don't mind pulling a wire through the firewall as I have done it SO many times it's not an issue at all. if there is a wire under the hood then perfect.

I am just wondering what all the other guys are doing because gauges are very common so I want to know where everyone else is getting power for them.

don't mind putting in a switch but then again I don't want to always remember to cut off the gauges.


I am up for anything just want it done right.

 

toyman

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Jul 19, 2007

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Vernon BC

Aug 14, 2011

#4

• Aug 14, 2011

• #4

I think BlackVert was suggesting that you use one of a couple of switched leads under the dash to trip a relay that feeds power from the battery to the gauges. Your ignition switch still turns the power on and off. From my schematic it appears you want to tap into is GY/Y.

 

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boostedSVT

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Aug 14, 2011

#5

• Aug 14, 2011

• #5

can't I just tap into the switched lead, wouldn't that work. Where are you hooking up electrical?

 

toyman

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Aug 15, 2011

#6

• Aug 15, 2011

• #6

boostedSVT said:

can't I just tap into the switched lead, wouldn't that work. Where are you hooking up electrical?

Click to expand...

Yes you can but you don't know what the additional load on that circuit will be. There is practically no load necessary to trip a relay. Wiring this way will give you 12 v to whatever current draw you need. I would suggest you use a 3 amp fuse in that circuit.

 

HISSIN50

"How long does it take to get help in here?

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Nov 29, 1999

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Aug 15, 2011

#7

• Aug 15, 2011

• #7

You could run the gauges off a large donor circuit from the interior fusebox (the HVAC fuse, etc). For the other stuff, I would do as suggested and drive them off a relay (are you sure the instructions don't call for that anyhow?).

 

BlackVert

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Oct 3, 2003

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Aug 15, 2011

#8

• Aug 15, 2011

• #8

toyman said:

I think BlackVert was suggesting that you use one of a couple of switched leads under the dash to trip a relay that feeds power from the battery to the gauges. Your ignition switch still turns the power on and off. From my schematic it appears you want to tap into is GY/Y.

Click to expand...

yes, that is what i was thinking. that is a very common approach

 

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boostedSVT

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Apr 10, 2004

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Aug 15, 2011

#9

• Aug 15, 2011

• #9

that works I don't have a/c so that would work fine. so here is what I understand from this.

run a 10 wire from the direct battery then have a wire from the hvac or any switched 12v to a relay and then from the relay have all the electrical working up to wires on that end.

anybody konw what type of relay that is. like the code number on thiers

 

HISSIN50

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#10

• Aug 15, 2011

• #10

FWIW, the HVAC fuse is for the blower motor inside the car. You probably still have a functional blower motor even if the AC has been removed.

A SPST or SPDT will suffice. Radio Shack and such stores should sell them. A Bosch style 30/40 relay should be fine.

Terminal 30 will get fused battery power.
86 will come from your switched positive source (the HVAC fuse, etc).
85 will be grounded.
87 will go to your accessories that are run off of the relay.

As Richard wisely noted, fuse the input (the relay coil on a relay of that size should not draw more than 500 mA). I would also individually fuse each accessory that receives power from 87.