Relay question

[Vulcan]

So I was looking for a place to tap into some 12 volt power in my 2004 Jetta TDI. After looking at the firewall I didn't see any easy access points (the car is well sealed). I pulled off the panels under the steering wheel and found a nice power source...There are several studs labeled 75A, 30A and Diesel. I checked them with my test lamp and found that they are always powered up which is OK as I plan on using a replay. As I need a 30 amp power source I plan to use one of the unused 30A studs. It does not have a relay in it from the factory like all the other ones that are currently in use. I pulled one of the replays and found that the unused one has a different pinout than the ones currently in use (The one I pulled uses a 4 blade connector and the unused one has a lot more connectors. Does anyone know what relay this takes or what it would be used for in another model of Jetta (perhaps its a gaser thing!). I took a few photos that I will post once I find my camera cable.

[Stonewall]

Re: Relay question

If you need a 30amp draw wire directly to the battery. You don't know what the current draw is on those wires already and you might start a fire if you overdraw the current on that wire. For 30amps you should also be using at least 12ga wire to be safe.

[Khyron]

Re: Relay question

There's several holes in the FW to get at the battery - I have a boost tube, a 12G amp wire and another wire all through 1 of them.

[Vulcan]

Re: Relay question

If you need a 30amp draw wire directly to the battery. You don't know what the current draw is on those wires already and you might start a fire if you overdraw the current on that wire. For 30amps you should also be using at least 12ga wire to be safe.

For a 30 amp draw you require an 8 gauge wire. The stud I was looking at using is currently unused in my car.

[Vulcan]

Re: Relay question

There's several holes in the FW to get at the battery - I have a boost tube, a 12G amp wire and another wire all through 1 of them.

Have you got directions to this hole? I stared at the firewall for a long time yesterday without seeing any usable hole.

[Stonewall]

Re: Relay question

All depends on the wire length The hole is hard to find from the engine side due to the material covering, if you take the undercover off near the pedals you will find the grommet just above and behind the brake to the right of the steering column mount.

[Khyron]

Re: Relay question

[Vulcan]

Re: Relay question

Thanks guys!!!

[Vulcan]

Re: Relay question

What is the vac. tube used for in your photos? What is the guage on the A pillar? What is the device in front of your shifter...iPod? What did you use for a mount? Enjoyed looking at your mods.

[Kor]

Re: Relay question

8ga seems excessive for 30 amps in a car:

http://www.batterieswholesale.com/ba...wire_gauge.htm

[Vulcan]

Re: Relay question

Here is the info I had on wire size...

# 8 AWG is rated for a maximum of 40 Ampere (note that temperature rates differ with each wire insulation style)

#10 AWG is rated for a maximum of 30 Ampere (note that temperature rates differ with each wire insulation style)

#12 AWG is rated for a maximum of 20 Ampere (note that temperature rates differ with each wire insulation style)



The electrical standard is to only load an Over Current device (fuse or breaker) to 80% (to avoid nuisance tripping and provide some room for fluxuations and surges. For example, the maximum rated load / draw that we would place on the above wire would be :



# 8 AWG 32 Amp (with a 40amp breaker)

#10 AWG 24 Amp (with a 30amp breaker)

#12 AWG 16 Amp (with a 20 amp breaker)



This allows you to protect the wire for its maximum rating, but reduces the chance of nuisance tripping.

[Khyron]

Re: Relay question

Not my car, just one of the many DIYs for boost gauge or aftermarket amps that use that main gromet/hole in the firewall.

Although I do have the same a-pillar boost gauge setup and like it very much.

[Stonewall]

Re: Relay question

All really depends on what you are doing, if you are running say lighting etc where you will be running 30A constantly then and over rated wire is the way to go. If you are using a relay it must be a monster of a relay with some heavy duty contacts if you plan on hooking 8ga up to it.
Nice chart Kris that is better then some I have seen (although I pulled the 12ga number out of my memory).