Dead tachometer, fuel economy gauge, and shift light.

[robschwieb]

Hey guys, I just bought a 1985.5 944 NA and have begun going through and sorting out some of the gremlins.

The current task at hand is getting the tach working. The car starts and runs fine so I think all of my sensors are good. I'm not getting any sort of needle movement. Same goes for the fuel economy gauge. Shift light isn't working either but I'm not complaining about that!

I opened the gauges last night and found a fried resistor. I can't find any bad traces on the board or direct shorts. I'm tempted to just replace it but something tells me it blew for a reason.

I found two other threads by the same member with a similar issue but his posts didn't make much sense to me and I'm not sure if he resolved it.

Threads: Tach guts and HG dme plug and tach 944S 1987

I was able to get a pic of the fried resistor as seen below.



Any idea on what caused this? Possibly a bad sensor or short that occurred for the previous owner and has since been fixed leaving behind a dead tach?

[Pauld_94S2]

From the other pictures, looks like either blue, red, brown, 620 ohm, or blue, red, silver, 6.2 ohms in either 1/2 or 1 watt metal film resistor. I don't think the 620 ohm would burn with 12 volts applied so it may be the 6.2 ohm value. You could try various values starting around 100 ohms and going lower in values until it either works or the resistor gets hot. Digikey or Mouser is a good source for resistors in small quantities.

However, I don't think replacing the resistor will fix the tach. Most likely there is something that is drawing too much current through the resistor, which is causing the burning. As far as I know, there aren't any schematics for the tachs.

If you really want to spend the time, replace the resistor and then remove all of the wires in the multi plug and put the +12 wire and ground back into the plug. Apply power and see if the resistor burns. If it doesn't, then add one wire back to the multi plug and repeat the cycle. Test after each wire you put back. If the resistor burns at some point, trace that wire you just added to wherever it is connected to using the service manual.

[robschwieb]

Originally Posted by Pauld_94S2

From the other pictures, looks like either blue, red, brown, 620 ohm, or blue, red, silver, 6.2 ohms in either 1/2 or 1 watt metal film resistor. I don't think the 620 ohm would burn with 12 volts applied so it may be the 6.2 ohm value. You could try various values starting around 100 ohms and going lower in values until it either works or the resistor gets hot. Digikey or Mouser is a good source for resistors in small quantities.

Thanks for the reply! If it were between brown or silver, wouldn't the resistances be 620 ohms or 0.62 ohms? A 0.62 ohm resistor seems kinda strange but then again, it is rather large compared to the other ones.