Z06Vette.com - Corvette Z06 Forum

Bad64Vette · 08-01-2002, 08:18 AM

The other day I inadvertently and unsuccessfully tried to burn my car to the ground. Well, tonight I think I am going to succeed. I think I will start by driving into a tree though. Can you sense a feeling of frustration?
I have read every post on here regarding MSD window switches and tachs. I have read tonybrasco's frustration and Z06175mph's comment on using pin 10 at the computer, which is what MSD is telling me to do. But I'll be damned if that works. Pin 10 at the computer is also pin A3 under the fuse block under the hood. The fuse block is much easier to get to. I started there and couldn't get it to work. So I resulted to taking the computer out the passenger fender, breaking the plastic bracket that holds the computer in the process. Nice when your best friend is the service manager. I tie into pin 10 at the computer, same damn thing nothing. I probe pin 10, it starts out at approx. 5.5 volts at start tup and climbs to a steady state 6.3 volts after about 5 seconds. Revving the motor does nothing to the 6.3 volt signal. Come to find out its a Class 2 serial data. If I cut pin 10 or A3 I do lose the tach in the car. So I have a very high confidence level I am on the right pin. I am toying with borrowing a oscilloscope and taking some snapshots just to see what the data line looks like. I don't see how anyone can get a shift light or window switch to work off of this, unless they have a module that can interpret this data and is not just looking for some DC voltage level. I pray someone can clarify this for me. If not I am going to say screw it, and put a button on the shifter, and simply activate it like I would in the old vette. This isn't what I want to do for fear of overrevving the motor, and really putting my friend on the line to warranty to a motor.

Sorry about the length.

TAMUz06 · 08-01-2002, 09:32 AM

Are you hitting PIN 10 on the right "strip"? It should be a white wire...

Bad64Vette · 08-01-2002, 09:36 AM

Yes, I can see its labeled pin 10 by the shell of the computer, and it is definitely white. Similiarly, if I cut it I lose my tachometer in the car.
Thanks for replying.

z06175mph · 08-01-2002, 10:43 AM

Bad64.

What kind of tach are you installing? The one I used, I had to clip a wire for V8 motors. Pin 10 can be confused with another white wire that very close to it. I made the same mistake at first and had it wired to the wrong one. I also heard that there was another location, under the steering column. You may have to search again for this topic on another corvette forum.

john

Bad64Vette · 08-01-2002, 11:05 AM

Thanks for input. I am installing an MSD Window Switch, PN 8956, I haven't clipped any wires. Clipping the wires will make it either for 6 cylinder, red wire or 4 cylinder applications, red and blue wires. I will look to make sure I haven't confused pin 10 with another one. I don't remember another white wire in the vacinity though. There is another easy place to access this same wire under the fuse box too. If I could figure out how to add attachements I would post the GM schematics for all of this. Then maybe someone could tell me what to do.
Thanks

Zed · 08-01-2002, 11:33 AM

I have been really wanting a shift light hidden in my vent, I thought that would be trick. Where do you guys find these things, and what is the MSD Window Switch?

Seth

vortech · 08-01-2002, 11:44 AM

Bad64vette are u sure that pin a3 is th same as pin 10 off the computer-if so that will save me so much time when i hook up my shift light this weekend.

Nemesis · 08-01-2002, 11:59 AM

If in fact you do have the schematics for the chip you can trace pin 10 through schematic to the right bus data line to a3 have you tried a continuity check with meter ? for a tone also with a scope if its digital you will look for data on chip to see if it triggers on rising edge and cutoff voltage to 6.3

Zed · 08-01-2002, 12:19 PM

Quote:

Originally posted by vortech
Bad64vette are u sure that pin a3 is th same as pin 10 off the computer-if so that will save me so much time when i hook up my shift light this weekend.

Where did you get a shift light?

Seth

Bad64Vette · 08-01-2002, 02:08 PM

Yes, I have tried a continuity check and they are the same. I will take some digital photos tonight, and I will also try to learn how to attach a file or jpg. Is it possible to attach pdf files that you can open with Adobe. If anyone wants the schematics PM me, and I will forward the scanned files.
I contacted MSD and talked to Lou, he seems to be the sharpest one there. He wants me to disconnect my white wire going to the MSD window switch, power on the car and verify that its setting at +5 volts. Evidentally he is questioning if whoever supposedly modified the box for me at MSD actually did it correctly. The window switch is supposed to look at the sine wave on the +6.3 dc voltage level. So the box should work using Class 2 serial data. I'm not convinced yet.

z06175mph · 08-01-2002, 07:55 PM

I will be removing my tach shift light this weekend, since it was just sold on Ebay. I'll try and take some pics for you.

john

Bad64Vette · 08-01-2002, 08:57 PM

Persistance pays off. I finally figured out that MSD screwed up. I shorted the "on" rpm chip and verified that the system worked. Then I decided to take a variable resistor/trim pot and turn it up from 0 ohms to see if I could get it to function. End result 304 ohms = 1100 rpm, 486 ohms = 2000 rpm, 638 ohms = 2300 rpm, 901 ohms = 3100 rpm, 1192 ohms = 3900 rpm. Now, I just need to extrapolate out and determine where I want it to turn off at. Now, I wonder if MSD will send me some variable chips or will they fix this damn thing. If nothing else I get to go racing Saturday night. Hopefully Monday I can post something better than a 12.81.
For everyones reference Pin 10 at the computer is the correct pin, you can also access it from beneath the fuse block underneath the hood. Its a white wire on pin 3 on the middle connector. To verify it simply cut and you will see you lose your tach. Its a lot easier than dropping the computer out the front fender. If someone will tell me how to attach pdf files I will post the schematics.
Later.

switchmaster · 02-17-2008, 05:46 PM

Is it possible to send me a picture of the wire and the placement of the wire. Thank you Jeremey

switchmaster · 02-17-2008, 05:48 PM

Wow forgot my email address is prb8shn@msn.com. Thank you for sending me the pictures for the tach wire hook up. Jeremey

redroket · 02-17-2008, 08:25 PM

I put in a Raptor shift light in a couple of weeks ago. You can get the tach signal from one of the white wires in the dash that comes down on the left side of the dash. If you stick it with a test light and you hit the correct wire the tach will jump. Took me about 1 hour to install and wire it in. I installed at eye level on the left windshield column. It looks fine and from outside the car you cannot see it. Hope this helps it is really easy, much eaiser than going through the firewall!