Speedometer, Tachometer, not moving

rogim46 · 02:36 PM

I'm trying everything I can to figure out why the speedometer and tachometer are not working on my 1985 (early) Porsche 944.

I can start the car and the MPG area on the tachometer works as I step on the accelerator. The first gauge also appears to be working (fuel, temp, etc). When I took out the gauges, I can shake the speedometer/tachometer and needles move freely. They just don't move when I press on the accelerator.

I already replaced speed/reference sensors and cleaned (most) grounds I could find.

I took apart the console to see what is going on there and found these wires not connected.

Could any of these wires be related to speedometer/tachometer not working?

What/where else should I be checking? Could the speedometer/tachometer be bad? Are they connected in a way in which if one does not work, the other stops working? Would a bad O2 sensor prevent the speedometer/tachometer moving?

I also have this relay sitting deep in dash, apparently not connected to anything. Anyone know what it could be for?

Bradical · 03-13-2015, 02:44 PM

1.) If it were the speed ref sensors the car would not be able to start because the fuel injection would not work.
2.) The O2 sensor wont stop the gauges from moving.

I hope someone else can offer some more help- sorting out that electrical should be priority one. I believe that black connector that you didn't circle in picture #4 is supposed to be connected to the gauges. I am not familiar with the early dash assembly though.

notMyScreenName · 08:17 PM

I'm not really familiar with the early cars electrical but most of those look like they are for the radio, and the one with the inline fuse (D) looks aftermarket. I don't think there were ever any inline fuses used on any of these cars (definitely not on the late cars). B and C are almost surely speaker connectors and the one below C in the first picture is the antenna.

Also, if it any help, on the late cars the tach is driven by the DME and the speedometer by a sensor on the transaxle. Other than power and ground the tach and speedometer are electrically unrelated. I'm almost certain that it's the same on the early cars but if I get a chance I'll check the diagram for the early 944 and confirm/correct this post as appropriate.

Edit to add: as h20cooled7 says below, on the early cars the speedometer is cable driven.

h20cooled7 · 03-13-2015, 04:07 PM

Dont early cars have a speedo cable? I know my 84 has one

rogim46 · 03-13-2015, 04:08 PM

I took a picture of my DME harness (early)

According to this:

Pin #11 should be the tachometer. I dont know much about electronics, but is there anyway to see what signal comes from pin #11 and/or if its even good?

I also took pictures of the wiring to the tach:

and the Speedometer:

rogim46 · 03-13-2015, 08:02 PM

Is it possible that the MPG needle on the tachometer works, but the RPM needle does not? Could this be a faulty tach, or bad wire/connection?

AA_Ezra · 03-14-2015, 12:13 AM

Early cars do have a direct speedo cable. It runs from the driver front spindle sticking out the wheel bearing hub cap, and a Dan. Of silicone in the middle of said cap to keep debris from entering and the c clip holding the speedo cable. Pretty sure that relay does not belong there. Behind the tack thee is a device looks like a mini of board with a pigtail that is bolted onto the rear of the tach ( might be speedo, it's been a while) and that I believe is what sends signal from tack to speedo or. Vice versa. Make sure the tach, speedo etc all are connected

v2rocket_aka944 · 03-14-2015, 06:27 AM

that relay is normal - its just an extra with function no one knows about but all early cars have it.

speedometer has a cable from the front left wheel to the speedo itself, yours is probably not hooked up (it makes it hard to remove/install the gauges)

the tach works without the speedo, but there is a plug from the speedo to the tach for the "upshift indicator" light.

thekidd · 03-16-2015, 11:54 AM

Try reconnecting the speedo cable on the back of the speedometer gague. Or, take the dust cap off the front left wheel, and see if you have lost the speedometre cable c-clip, possible broken cable.

rogim46 · 03-16-2015, 01:56 PM

Quote:

Originally Posted by thekidd

Try reconnecting the speedo cable on the back of the speedometer gague. Or, take the dust cap off the front left wheel, and see if you have lost the speedometre cable c-clip, possible broken cable.

I tried this. As I spin the part of the cable connected to the dust cap, it spins the cable by the speedometer.