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Question Major Electrical Help Needed, Please Help

Hey guys I will try and keep this short. Recently I bought a '84 NA and it has seemingly many electrical problems. Try and stick with me here because I know that together we can figure this out! I do not know what of the following is related or separate so I will just list all that I know:

-First major problem is a short somewhere in the #7 fused circuit(radio, cig lighter, interior lights, clock, etc).
-The wiring behind the stereo seems pretty chaotic and previous owner had run a new positive lead to the steareo in order to at least have it work.
-Second major problem is when the headlights(which work) are switched on the temp gauge bounces to zero(all the way left), the tach drops about 800 rpms and the oil pressure gauge drops about 1 bar.
-All the time the temp gauge reads low(only ever reaches middle of bottom black section when hot) but I am pretty sure the sensor sender is producing the correct resistance values (I tested).
-The original tach did not work (although the economy thingy did) when i bought the car so I switched it out with one that the previous owner already had. The new one was not as deep and had different numbers on the side but the tach on it works(but the economy thingy on it does not now?) could it possibly be a wrong tach causing problems? also when I plug the brown ground into the light on the back of it, it causes the temp gauge to bounce to zero(all the way left) just like when the headlights are switched(mentioned above).
-The car idles way low for a few mins on startup(when cold) then too high forever after that(1.4k rpms) but I am almost positive that the dme temp sensor for that is bad because I disconnected the sensor and plugged the correct resistors value across the connectors and got it to idle correctly.
-The roof hatch motor in rear does not move anymore when the switch is pressed, although I can hear a relay click in the rear.

So its gotta maybe be the short or a different one that is causing gauges to react when the headlights are switched? I have the online porsche wiring diagrams but the systems are extremely complex. Please help guys!

If you guys want like a video or photos of any of this just tell me. Any ideas about any or all of this is welcome. Thanks So Much in advance!
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1884 Porsche 944
Old 10-08-2011, 01:44 PM
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Quote:
1884 Porsche 944
Damn.
No wonder you're having problems.
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Old 10-08-2011, 03:17 PM
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Quote:

Quote



1884 Porsche 944

Damn.

No wonder you're having problems.
Funny thing is the car runs great and the problems seem so minor when actually driving. It's just when I stop and think about it it's like woh. But it's gotta be something so simple I know it
Old 10-08-2011, 03:24 PM
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Your method of getting the DME engine temp sensor to work is interesting. Good work.

Your signature line should be corrected --- 1984 Porsche 944

The rest of your electrical problems need to be worked out with the wiring diagrams.
Pelican has them here:
Pelican Parts: Porsche 924/944 Electrical Diagrams

The tach should be OK but there are many on ebay to begin to get everything back to normal.

GL
John
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Old 10-08-2011, 04:14 PM
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aalong,
1. Get rid of the aftermarket tach unless you know all it's specs and hookups and you're sure it's totally compatible.
2. The radio install could have messed up things. Check that area out carefully.
3. Check your grounds under the dash. There's a "crown" of grounds on the left side.
4. Brown is usually ground, but the gauge light bulbs are usually powered by a gray/blue wire, which is daisy-chained. The ground is also daisy-chained.
5. The early 944 wiring diagrams (actually current flow diagrams, SUCK). Here's the trick! Go to the later models section of the diagrams and find the 924S model. It's the same early chassis as the early 944's but in the easier to use format of a real wiring diagram.

The headlights thing is scary. Next, you'll see a smoke cloud from under the dash! Your headlight switch might already have damaged wiring. Check your headlight motor for easy, smooth operation. Headlight motor relay not corroded? Check and clean the major chassis grounding points on both of the longitudinals right behind the headlights. Remember, you're in New York -corrosion.
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Old 10-08-2011, 04:18 PM
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Well the headlights operate correctly and the tach looks identical but maybe for a different year?
Old 10-08-2011, 04:22 PM
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Tachometer for an '83 will not work on an '84.
The temperature gauge connection on the back of the '84 is different from a '83, making the gauge read below the scale.
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Old 10-08-2011, 05:11 PM
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The gauges going funny when switching on the headlights is definitely a ground. I wont say what to do or where to look because I'm not 100% sure since it's an early car and I do not want to lead you in the wrong direction. I'm sure someone else will be able to give more details but I know in the late cars the headlight grounds are under the hood and near the drivers side headlights.
Old 10-08-2011, 05:20 PM
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Major earth problems I would say
Old 10-08-2011, 06:33 PM
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Marajit ok I'll try disconnecting it and see if it helps. Fwayfarer ok I cleaned the one main grOund behind driver side light. And psgr side is tough to get to. I'll also do the ones behind the gauges. And porschetub what?
Old 10-09-2011, 05:58 AM
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I had a different Tach (no upshift light) in my car that totally messed up everything. When replaced with the correct 1984 Tach with the up-shift light, everything returned to normal, gauge wise. Check grounds but find the correct Tach, too.
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Old 10-09-2011, 06:08 AM
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Okay wow sweet. How much of my problems do you think could be caused by it? And would unplugging it make some other things operate correctly? So that way I can test if that is the problem
Old 10-09-2011, 06:18 AM
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Hi,

I had similar symptoms in my 924S (which is very similar to the early 944s). I cleaned the grounds under the dash in the footwell and the smaller of the bellhousing grounds (I found it nearly impossible to get the larger one off, so figured I'd wait until I took the intake manifold off.

My gauges were affected by the lights; the fuel gauge would say it had more fuel when the lights were on (though low warning light still came on at the right level), and the temp gauge increased a bit when lights were on.

I wired a relay system into the lights (HondadustR did a very good write up, and Daniel Stern's website tells you pretty much all you need). This made the headlights brighter but didn't stop the gauges reading differently when the lights were on.

I'd start by cleaning all the grounds (if you can get to the big one on the bellhousing great, but if not running an extra ground from engine to body might help). If this still doesn't fix it you might have to either live with it or rewire the whole car.

Good luck.

Mike
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Old 10-09-2011, 07:08 AM
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I'd start with tracing the shorted #7 circuit. It could be shorted to other wire(s), causing the other issues. It that's not it, then it's time to get DOWN. Down on the grounds, that is!
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Old 10-09-2011, 08:17 AM
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Okay guys I'll try all the other grounds. Any other ideas?
Old 10-09-2011, 08:52 AM
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Are you aware of the grounds on the back of the instrument panel? (you would need to pull it)

They can (and do) play havoc with the instrument panel gauge readings, as do bad grounds in other places.
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Old 10-09-2011, 09:04 AM
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Yea I have read a lot of about the grounds behind. Fortunately I have taken the dash out many times
Old 10-09-2011, 11:26 AM
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You're ahead of me then. I've never done it yet. But it would definitely be nice to see all of the gauges operating correctly for the first time in my ownership of the car.
Old 10-09-2011, 03:39 PM
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Where exactly are the ground points under the dash; MPII & MPIII ?
Old 05-27-2014, 09:30 AM
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Under the drivers side dash in a multi post "football"
Above the fuse and relays
Welded to the underside.
Lay on your back and look up.
Enjoy



J_AZ
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Old 05-27-2014, 09:41 AM
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