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Gauge wiring

 
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bureau13  



Joined: 07 Sep 2017
Posts: 469
Location: South Florida

PostPosted: Sun Feb 13, 2022 3:41 pm    Post subject: Gauge wiring Reply with quote

There appears to be some serious f*ckery in my leftmost gauge pod from a PO. Check this out:

https://photos.app.goo.gl/tprG2QqM3FWPp3UA7

https://photos.app.goo.gl/oHaJA7bfcwRhVamA8

I guess they ran a wire from the (hot?) side of one of the lamps (empty fuel light maybe?) and spliced it into a wire that's part of the large connector. Looks like white or light grey with a blue stripe, which is some sort of gauge lighting wire I think? But I'm not sure what's going on here...is that taking power TO gauge lighting or FROM it. FWIW, my nighttime gauge illumination is not working, so maybe there was a bad connection somewhere and their fix was to take it from the empty fuel warning lamp? And now that has maybe lost connection? I don't know.

I especially like the homebrew strain relief of running the wire under the connector. [/url]
_________________
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1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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Eliza  



Joined: 17 Aug 2015
Posts: 174
Location: Prov. Utrecht, The Netherlands

PostPosted: Mon Feb 14, 2022 5:19 pm    Post subject: Reply with quote

Interesting .

Yes, grey with blue tracer is power supply for dash lighting.

There's two bulbs in the multigauge for backlighting, do they both not work on yours?

You may want to take the multipin plug off and see if you get 12V on the gr/bl wire with ignition on and dash lights on. If not, that red wire was likely installed to get power TO the lights...

If yes, ditch the red wire ( where's its other end, can you find that at all? ), take the multigauge apart at check the circuit board for loose contacts. It's really easy to do, and refreshing it will help with twitchy gauge needles and the lot.

This is the only one of the three round instruments that can be opened without having to remove the bezel round the front, so go for it I'd say

Shout if you need more info.

Eliza
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1985 924 NA RoW
1981 931 S2 RoW
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bureau13  



Joined: 07 Sep 2017
Posts: 469
Location: South Florida

PostPosted: Tue Feb 15, 2022 1:07 pm    Post subject: Reply with quote

That's great info, thanks! I will give that a go. It looks like the red wire is coming from the hot side of the fuel low warning lamp and splicing into the grey/blue, so that makes sense that it was a "fix" for no backlight. The thing of it is, I have no backlight in ANY of the gauge pods right now...would supplying +12V there supply light to all pods?

I don't suppose you know where power comes in to the battery/charging system lamp? That on is not getting +12V either. Coincidentally, I'm not charging either, which is actually a bigger problem than the lack of gauge backlighting. The car sat for over a year while I was waiting for the head to come back, and I didn't touch any of this dash stuff but apparently it didn't like sitting there doing nothing.

Eliza wrote:
Interesting .

Yes, grey with blue tracer is power supply for dash lighting.

There's two bulbs in the multigauge for backlighting, do they both not work on yours?

You may want to take the multipin plug off and see if you get 12V on the gr/bl wire with ignition on and dash lights on. If not, that red wire was likely installed to get power TO the lights...

If yes, ditch the red wire ( where's its other end, can you find that at all? ), take the multigauge apart at check the circuit board for loose contacts. It's really easy to do, and refreshing it will help with twitchy gauge needles and the lot.

This is the only one of the three round instruments that can be opened without having to remove the bezel round the front, so go for it I'd say

Shout if you need more info.

Eliza

_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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Eliza  



Joined: 17 Aug 2015
Posts: 174
Location: Prov. Utrecht, The Netherlands

PostPosted: Tue Feb 15, 2022 3:15 pm    Post subject: Reply with quote

First the alternator idiot light: pin 11 of the round multiplug on your multigauge has a blue 0.5 gauge wire going to term. 2 of plug D at the rear of the fuse box.

From term. 2 on plug C at the rear of the fuse box, a 0.5 gauge blue/white wire goes into the engine bay, changes colour to blue somewhere on the way and ends ( or actually starts ) at the three-pole plug for the starter wiring loom.
On the other side of that plug, you should see a black 1.0 gauge wire going to terminal D+ on your alternator, that is the exciter wire.
Indeed, if no 12v at pin 11 of your multipin plug at startup, no exciting of the alternator magnetic field and no charging. You should be able to check continuity from the three-pole plug in the engine bay to pin 11 of the gauge's plug. If that's ok, suspect the connection at D+/alternator, or the wire between alt. and three-pole plug.

The dash lights... that's intricate. You say no backlighting in any of the pods - does that include the three gauges in the center console? No backlights at all?

Eliza
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1985 924 NA RoW
1981 931 S2 RoW
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bureau13  



Joined: 07 Sep 2017
Posts: 469
Location: South Florida

PostPosted: Wed Feb 16, 2022 11:41 am    Post subject: Reply with quote

Correct...no backlighting of any of the gauges, either the three main gauge pods or the center console gauges. Are they all fed by that grey/blue wire (or other wires connected to it)? If so, maybe the red wire hack was intended to address all of that.
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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Eliza  



Joined: 17 Aug 2015
Posts: 174
Location: Prov. Utrecht, The Netherlands

PostPosted: Wed Feb 16, 2022 3:24 pm    Post subject: Reply with quote

If there's no interior lighting at all (except for courtesy lights, they are powered differently ) then suspect your light switch and its connection(s), the starting point of the dash lighting circuit.

Here's a wonderful tutorial on solving problems with it, with pictures and explanations on how to check the switch itself: http://944foot2thefloor.blogspot.com/2015/10/how-to-troubleshoot-porsche-944.html

Scroll down the page half way, the top half will not be applicable for you ( I suppose ).

In a few of the pictures you can see the gr/bl wiring which then worms its way all the way to the glove box light.

Let me know if you'd like the MY 1982 ( or MY 1981 ) wiring diagram, I can send it to you by email.

Eliza
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1985 924 NA RoW
1981 931 S2 RoW
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bureau13  



Joined: 07 Sep 2017
Posts: 469
Location: South Florida

PostPosted: Thu Feb 17, 2022 3:27 pm    Post subject: Reply with quote

That tutorial looks excellent, thank you! I will probably not be able to dig in until the weekend.

I'll send you a PM with my email, the wiring diagram should prove helpful as well.
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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bureau13  



Joined: 07 Sep 2017
Posts: 469
Location: South Florida

PostPosted: Mon Feb 21, 2022 1:33 pm    Post subject: Reply with quote

UPDATE: I found the problem with the charging circuit. It appears the wire that connects to the exciter had a break (when I changed the head I didn't remove the alternator, I just flipped it out of the way. Probably not great with ancient wiring). I put fixed that and now the battery light comes on when I first turn on the ignition, and goes out when I start it, and I'm getting higher than battery voltage from the alternator now when the car is running. That's problem 1.

Oddly enough, my gauge backlighting is now also working, EXCEPT for that multi-gauge pod on the left, where the hacky wiring was. Oddly enough, I was getting 12V at that bulb, but maybe I was measuring from the red wire and me messing around with it has caused the red wire to no longer be connected to the actual bulb terminal? That's assuming the red wire is intended to make up for a problem with that board, and provide current from the grey/blue wire via this secondary path. The lower backlight lamp was not getting 12V at all, so it kinda makes sense. I think. What's weird though, is I do not know what restored the rest of the backlighting, to the other two pods and the center console gauges.

I will attempt to confirm my theory on the intentions for that red wire, and then see if I get it connected back up, what happens. Anyway, it's getting close!
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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Eliza  



Joined: 17 Aug 2015
Posts: 174
Location: Prov. Utrecht, The Netherlands

PostPosted: Mon Feb 21, 2022 6:41 pm    Post subject: Reply with quote

Good job!

About the multigauge backlighting. On that round plug that goes into it, the grey/blue wire on terminal 3 of the plug does have 12V when your dash lights are on? Maybe that wire is loose or the female socket in the plug has play?

I could imagine your PO tried to tie the backlighting of the multigauge into the rest, coming ( maybe ) from the tach or speedo. The backlighting ( as you now know ) is all interconnected, and the multigauge is the last in line.

Eliza
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1981 931 S2 RoW
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Eliza  



Joined: 17 Aug 2015
Posts: 174
Location: Prov. Utrecht, The Netherlands

PostPosted: Mon Feb 21, 2022 6:53 pm    Post subject: Reply with quote

Took another look at your second photo. If I see this correctly, the red wire would around the upper of the backlights originates at that plastic splice thingy, so I'd assume your PO found there was voltage at the grey-blue wire going into the multigauge but not reaching the bulb holders. Instead of opening the gauge and repairing the circuit board he used the red wire to connect the bulb externally.

If I were you, I'd verify voltage at pin 3 of the plug the open the instrument and restore it to working order. It's really not hard to do, and you can clean and retighten everything in there while.. you're in there .

Let me know if you need help or encouragement. I seem to remember seeing a how-to with photos on multigauge refurbishment on the web somewhere...
Indeed. Here goes. Site is in German, but Google Translate should make short work of that : https://www.stinni.de/index.php/porsche/tipps/87-kombiinstrument-instandsetzen

Eliza
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bureau13  



Joined: 07 Sep 2017
Posts: 469
Location: South Florida

PostPosted: Tue Feb 22, 2022 2:07 pm    Post subject: Reply with quote

I think you're right about that red wire, and I suspect it is a problem with that board. It does seem like something that is not probably too difficult to dig into.

I actually took German in high school. But that was a LONG time ago I'll see what I can do...thanks again!

Eliza wrote:
Took another look at your second photo. If I see this correctly, the red wire would around the upper of the backlights originates at that plastic splice thingy, so I'd assume your PO found there was voltage at the grey-blue wire going into the multigauge but not reaching the bulb holders. Instead of opening the gauge and repairing the circuit board he used the red wire to connect the bulb externally.

If I were you, I'd verify voltage at pin 3 of the plug the open the instrument and restore it to working order. It's really not hard to do, and you can clean and retighten everything in there while.. you're in there .

Let me know if you need help or encouragement. I seem to remember seeing a how-to with photos on multigauge refurbishment on the web somewhere...
Indeed. Here goes. Site is in German, but Google Translate should make short work of that : https://www.stinni.de/index.php/porsche/tipps/87-kombiinstrument-instandsetzen

Eliza

_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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View user's profile Send private message
bureau13  



Joined: 07 Sep 2017
Posts: 469
Location: South Florida

PostPosted: Sun Feb 27, 2022 1:41 pm    Post subject: Reply with quote

Eliza gets another prize. I pulled apart the multi-gauge as suggested, and ohmed out all the traces. Sure enough, the on from where the grey/blue wire comes in through the connectors was not making it to the backlight bulbs. You can see why in the attached phone: Hairline crack. I soldered a small jumper wire directly to the board, bypassing the crack, and I have proper connectivity now (I haven't reinstalled it in the car yet but I'm certain this will fix it).

https://photos.app.goo.gl/7oidXvxL5WDzwFndA
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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View user's profile Send private message
Eliza  



Joined: 17 Aug 2015
Posts: 174
Location: Prov. Utrecht, The Netherlands

PostPosted: Mon Feb 28, 2022 3:15 pm    Post subject: Reply with quote

Thanks - glad it worked out for you!

Well done!


Eliza
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1981 931 S2 RoW
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