choinga

I've got my MAF power wire running up into the fuse box and tied into the fuel pump fuse for switched +12V.

I'm about tired of looking at that - need to clean that up...

Anyone know where I can find another +12V source in the engine bay?

The Vitesse intstructions indicated that I *may* be able to find it at the test port - but none of those ports shows +12V in my car.

dillon410021

my maf is hooked up to the test port
I will go look now at which hole

dillon410021

heres a photo

JohnKoaWood

Ignition coil is a switched 12V, the trigger signal is on the ground.

Test port, gauge pass thru (on firewall just behind the test port), and many other sources inside the engine bay... I can double check the FSM diagrams when I get home...

You could also tap a relay into the radiator temp sensor power lead, and use the relay to switch 12V right off the battery!

V2Rocket

coil

choinga

Thanks Dillion - I've already been through that with my multi-meter. I 'assumed' the one port would be 12V during the install based on John's directions and my car would barely start. Once I got the MM out, there was something like +6V hitting that port, so no wonder. Apparently, in true Porsche fashion - not all cars have the same voltage to the various test ports...for whatever reason...

For the coil - are you recommending just pulling the plug wire off the top and wiring the MAF power wire right into that?

JohnKoaWood

No, tap into the wire connected to the + terminal on the coil... it is a switched 12V. for safety you can issolate it using a relay... the trigger signal for the coil is the ground, not the hot... the + terminal should have 12VDC whenever the key is on. there are several other spots under the hood, but the coil is one of the easier ones to get to!

choinga

thanks - any suggestions on what relay I should wire into that setup?

JohnKoaWood

Any 12 V relay, and an in line fuse, run the switched lines from the battery to the MAF, tap the trigger wires for the relay into the coil hot line.

Maf shouldn't pull more than 1-2A, so size your fuse appropriately, and the relay can be 10A...

install can be as clean and hidden as you like to make it!

You could also tap directly into several 12V lines on the firewall going to the pass thru for the gauges...

choinga

Thanks Jon - would this work?

Looks like this covers both the relay and fuse in one shot. Judging from your response the white wire would go to the battery positive and the black wire goes to the +12v on the coil which triggers the relay to close the loop and send power to the MAF when they key is turned?

JohnKoaWood

Should work fine, I usually get my relays from Radio Shack or local parts store, but Amazon works too!

choinga

okay, got the relay in the mail today - two wires seem fairly obvious given the conversation - but there are 3 relay wires...anyone wanna take a guess how I should wire this thing up?

I'm guessing red to the battery postive terminal, black to common ground somewhere and yellow goes to the ignition coil positive. Not sure what I'd do with the other two leads - just tape them off, I guess.

onspeed

I'm not entirely sure what you're trying to do, but I think it's to power the MAF using the switched power wire from the coil? Correct me if I'm wrong but I think you need to connect 85 to ground, 86 to coil wire, 87 to battery, and 30 to MAF. Connecting 86 to the battery would cause terminal 87 and 30 to always be connected, meaning the relay is purpose defeating... at least that what it looks like from that diagram. And you're still going to want to run a fuse inline.

choinga

Thanks Chris - it's been a long day, I have the flu (and my kids do too...)...I was approaching this backwards. Yes, I think that might work.

Yes, it's to power the MAF - trying to clean up our wire mess post-turbo job.

If the MAF won't pull more than an amp or two - what size fuse should I get? 5A?

I'm assuming that fuse should be spliced into the wire that goes from this relay to the MAF?

JohnKoaWood

OK, connect 86 to the power feed to the coil, the other side to ground (use a big resistor as you dont want to ground out the coil feed)

30 to battery with an in line 5A fuse, 87 to the MAF, 87A not connected to anything!

Turn on the key and it should supply 12V to the MAF... turn off key and 12V should also turn off.