M50NV swap, Tach used to work, but not now.

[SkorcherX]

Hey guys,

So I had the battery disconnected from the car for a few months while I was redoing the interior. I got everything back together and much to my dismay my tach doesn't work now. It did prior to me tearing apart the interior and the dash.

I googled around and found that the batteries on the SI board are only good for about 72 days a piece, as they get recharged by the car battery.

Well I took the instrument cluster apart and used a voltmeter to test the batteries. Well shit, these things have about 0.8v in them. This must be the reason my tach and econo gauge no longer work.

I order new batteries and test them on the voltmeter before installing them. Both are about 3.1v. This is great. I get them installed and get the cluster back in the car. Fire it up.... No tach, no econo gauge. WTF?!

I am at a loss here. I tested the wires that go through the glove box for at the C104. I have a Black wire, and a Black/White wire. Black/White goes to a White/Yellow, and the Black goes to the other Black wire. This is how I had it prior to pulling the dash, and is how it remains.

What else can I test to troubleshoot this? The car runs and drives just fine, but not having a tach makes me feel like the car is incomplete. Any help is greatly appreciated. Thanks!

[StereoInstaller1]

what year/model?

[SkorcherX]

87' 325 (built 11/86). 92' NVM50.

Also... 10" Luke Box sounds great, Luke!

[StereoInstaller1]

Hmmm. Did you connect the black wire in your dash to the one on the DME?

Good to hear yo have proper bass...pimp that shit out, we need sales bad!

BTW, I made a thread about this, but I cant remember what I called it and could take days for me to find it...and I wrote the fucker! Might be worth it for you though, as there are pics.

You coming Sunday?

Luke

[SkorcherX]

Yes I connected the black wire from C104 to the black wire on the DME.

What is on Sunday?

Is this your post your referring to?

http://www.r3vlimited.com/board/showthread.php?t=213404

Thanks.

[greyis89]

Just some dumb troubleshooting advice. I tried to hook up my dome lights and blew a fuse that worked those, the glovebox light and tach aparenly because they all quit. New fuse brought back the glovebox and tach so I said screw the dome lights. Might help idk. Also and 87.

[SkorcherX]

Just checked Fuse 21/10/24. All are good. Everything appears to work sans the Tach/Econo gauges. Super frustrating.

I also just tried another coding plug. This has no effect.

[SkorcherX]

OK, I just jumped the black wire off the DME to some of the pins on the blue plug on the back of the instrument cluster. One pin will give me the temp gauge. Which is cool but that works without issue. I continue on until I find a pin that causes just a small flicker of life in the tach.

Anyone encounter something like this? Does this help at all? Any response is appreciated.

Thanks.

[drken]

If you had much of the dash apart, look for a second c104 connector lying around near the place you connect it to the DME. I believe my car had 2 connectors, and I believe one was for the OBC, and the second runs straight to the cluster for tach and econo functions, probably for cars that had no OBC. You may just have it connected to the "other one".
Hope this helps.

Ken

[SkorcherX]

So, I put on an after market Molex connector when I did the swap (for the Tach and Econo wires from the ECU) replacing the C104. So if there were two similar plugs in the glove box area, mine would only fit into the one. Which is what worked prior to removing the dash.

So I also just testing the voltage coming from the two wires from the DME. At idle, no voltage change, then when I revved it up, they would change. I believe this tells me that the DME indeed providing a signal for these instruments. How can I figure out why they are not operating accurately?

I am super stumped. 328iJunkie, Nando, StereoInstaller... Any sage words of advice?

[ScHpAnKy]

check your harness - tach was pin #9 on the E30 side, it needed to be run to point #20 on the e36 side.

[SkorcherX]

check your harness - tach was pin #9 on the E30 side, it needed to be run to point #20 on the e36 side.

I think this advice is for a different model? Below is how I have it wired up. This has not changed after the dash was taken out and then put back in.

pin 24 on the e36 goes to the white/yellow wire of the c104 (Econo Gauge)
pin 14 on the e36 goes to the black wire of the c104 (Tach)
pin 20 of the e36 goes to the wire on the back of the instrument cluster in the circuit board with the green covering that snaps onto the cluster. (VSS)

My tach used to work. Dash came out, got flocked, stereo got installed, dash went back in. The engine harness and DME never got unplugged (including the C104 connection). In fact I drove the car around with no instrument cluster or dash when I had to move it in and out of the garage.

[StereoInstaller1]

Did you get this figured out yet?

[SkorcherX]

Did you get this figured out yet?

I have not. I have a cluster from a 325e. I tossed that in. The tach and econo gauge didn't work either. I am thinking that something from the stereo install fucked this up. I didn't do it.. My buddy did. So I'm not quite sure what it could be.

[SkorcherX]

Monday Morning Bump.