924Board.org

[ideola]

I picked up a complete set of dash gauges from an early 944. The Bevel is the interchangeable, and the multi-gauge and speedo are too, of course. But to my chagrin, the tach has a different wiring setup.

On the 924's, there are just three wires: green, black, and brown. On the 944 tach, there is a plug receptacle for an 8-pin harness. The pins are labeled as follows:

1 2 3 Hg
4 5 6 H+

The Hg and H+ have a special harness that plugs to the speedo for measuring instant fuel economy. That piece is intact. Any ideas how or whether I can wire up my tach leads from the harness so that the tach functions?
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erstwhile owner of just about every 924 variant ever made

[ideola]

bump
_________________
erstwhile owner of just about every 924 variant ever made

[924guy]

http://www.pelicanparts.com/944/electrical/944_84_4_2.jpg

okay, it looks like your "h" wires are indeed tied into the speedo.
then it shows the lighting circuit..that the easy stuff.

theres six spades left, it looks like tabs 4/5/6 go to the DME , .. but it also looks like there are other functions integrated into the late model tach, possibly an output for a rev limiter..hard to tell.. ive got three different books here im looking at, as well as the above linked diagram, and theyre all slighly different, so its hard to say what is what. what we need is an output diagram for a 83+ DME, and one for a motronic box, i think. or a feed diagram for the vdo tach (better)

I took mine apart ( i hate you, this will drive me nuts until we figure it out, i want to add the late model gauges in my 931, just for the stupid mileometer, and the 160 speedo) ..the internal lugs are marked:

hg=hg
h+=h+
1 =Qe
2= no marking, but looks to be directly tied to Hg (tested, have continuiety)
3= 30
4= 31 also has a "+" next to it, but ties into the ground wire inside the casing.
5= 15 and appears to be tied to h+
6= 1

, spade 1 is the coil signal, and spade 4 is the ground. theres allot more to it though before id plg it in, have to figure out which wires go to the dme (looks like 4.5.6) and what the other three wires do...

so basically, no answer, but a bit more info ...ill keep trying..
_________________
Eric
78 924
82 931 SE "smokey"
99' VehiCross
Y2K Honda Insight
http://www.cardomain.com/id/924Guy
Performance by Pasha

[ideola]

I hate trying to read those diagrams! Gotta learn how one of these days...

Anyway, you list spade 4 twice, once as the 12V in and once as the ground ... was that a typo?
_________________
erstwhile owner of just about every 924 variant ever made

[924guy]

mistake, i fixed it.. i thought 4 was the 12v in, until i got out my tester and found it had continuity with the groud strap inside the caseing...
_________________
Eric
78 924
82 931 SE "smokey"
99' VehiCross
Y2K Honda Insight
http://www.cardomain.com/id/924Guy
Performance by Pasha

[ideola]

I think spade 4 is in fact ground. When I plug in the earth lead to it, and put in one of the lights with the lights on, I get nice bright light. Interestingly, if I move the ground to spade 5 or 3, the light also lights up but much more dimly.

So, the fact that this car doesn't have a DME, doe that mean I have to do some additional wiring, or should I be able to plug 12V lead and the coil lead into the correct spades and get the tach to work?
_________________
erstwhile owner of just about every 924 variant ever made

[924guy]

im thinking its just a matter of finding the right spades to plug into, but the dme leads concern me. i dont know if they feed the tach , or alter input current in some way. if they do, then we might need to step down the input current... im hopeing someone here cn chime with a bit more info..
_________________
Eric
78 924
82 931 SE "smokey"
99' VehiCross
Y2K Honda Insight
http://www.cardomain.com/id/924Guy
Performance by Pasha

[PORSCHEV]

Hey guys...I know this is OT from what your working on...but do you know how to calibrate the early 924 tach to read off a V8 chev distributor. The GM distributor only has 1 wire coming off for the tach? Can you help??
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1976 924
5 lug conversion, 17'C2 wheels,custom body work,327 vette engine.

1978-#53 "D" track racer.

[924guy]

im guessing youd need some sort of pulse converter to make the signal readable. the tack has "4 zyl 247khz" stamped on it, which im assuming is the freqeuncy pulse for the avg porsche 4 cylinder . the 8 cylinder is going to have a different signal, so youd need to either modify the reciever in the tach to what ever that frequency is, or use a converter of some sort.
there has to be an equivelnt sized tach that will work with the chevy, or at least a selectable one(4/6/8 cyl) out there someplace. i think that owuld be the better solution rather than trying to convert a 4cyl. one..
_________________
Eric
78 924
82 931 SE "smokey"
99' VehiCross
Y2K Honda Insight
http://www.cardomain.com/id/924Guy
Performance by Pasha

[Lizard]

Hey Adam,
for your tach, 1 wire will be ground, one will be 12V +, and the last will be the single trigger wire, take the tach and pop the lens ring off, then the back, then hook up the signal wire and then make a jumper for the +and - so that it is in the engine bay and start the car, you can then see what it is reading and there is an adjuster that you can turn which will give some adjustment, dont know if it will be enough though, use a timing light to check of course.

I havent seen you on msn much lately (though I havent been online myself much), I am normally on abit later now though, have you just been too busy?
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3 928s,

[ug]

To use early 944 tacho in 924 it's easy.
You have 3 wires in your 924:
- green - ignition coil pulses
- black - (15) +12V
- brown - earth
So, connect the green wire to spade #6 of the 944 tacho, black wire to spade #5 and brown wire to earth spade.
_________________
Euro 924 '85 016/8 4-wheel disk brakes

[PORSCHEV]

Lizard,
Somehow your not on my list anymore????? I can't find your name anywhere in my address book either. Whtas your handle agian for msn or try adding me agian. I was going to ask you about something the other nite and noticed you weren't on my list.

My computer keeps picking up these god damed porno viruses that pop up....and shuts me down. It's going in for a format soon.

[924guy]

[ideola]

It's not working for me. I'm not sure if I got a bad tach or what, but it doesn't work with the green wired to 6, black wired to 5, and earth to 4.
_________________
erstwhile owner of just about every 924 variant ever made

[ug]

Spade #4 is not a ground. Ground spade must be somewhere on the tacho body (must be connected directly to the tacho body). Try to connect brown wire to steel tacho body.
_________________
Euro 924 '85 016/8 4-wheel disk brakes