Any electrical geniuses?
03-22-2009, 10:21 PM
#1
Rennlist Member
Thread Starter
Any electrical geniuses?
'84 944...
Since I've rescued this car, the tach was a "some of the time" thing, then pretty much stopped. Searches brought up lots of talk about the reference and speed sensors, but both tested OK. And the mpg meter and annoying up-shift light both worked. Got a good used tach off eBay, slapped it in, and it works all the time. But... the old tach had a grounding tang on it, this one didn't. I added one, and hooked it up. When the ground is connected, the temp gauge pegs. When disconnected, it gives a mid-range reading on a cold engine. With the old tach, it worked sporadically (mostly correct, sometimes would peg).
Here's the freakiest part. The mpg meter in the new tach (which was from an '84 also) doesn't work unless the lights are on! Then it immediately functions. This is independent of the grounding situation.
The gauge lights in the tach don't work unless it is grounded (no surprise).
I have been thru the manual's circuits and can't find anything that could cause this. The wiring all looks cherry, no sign of any fires or "smoke releases".
Any ideas??
Since I've rescued this car, the tach was a "some of the time" thing, then pretty much stopped. Searches brought up lots of talk about the reference and speed sensors, but both tested OK. And the mpg meter and annoying up-shift light both worked. Got a good used tach off eBay, slapped it in, and it works all the time. But... the old tach had a grounding tang on it, this one didn't. I added one, and hooked it up. When the ground is connected, the temp gauge pegs. When disconnected, it gives a mid-range reading on a cold engine. With the old tach, it worked sporadically (mostly correct, sometimes would peg).
Here's the freakiest part. The mpg meter in the new tach (which was from an '84 also) doesn't work unless the lights are on! Then it immediately functions. This is independent of the grounding situation.
The gauge lights in the tach don't work unless it is grounded (no surprise).
I have been thru the manual's circuits and can't find anything that could cause this. The wiring all looks cherry, no sign of any fires or "smoke releases".
Any ideas??
03-22-2009, 10:31 PM
#2
Nordschleife Master
'84 944...
Since I've rescued this car, the tach was a "some of the time" thing, then pretty much stopped. Searches brought up lots of talk about the reference and speed sensors, but both tested OK. And the mpg meter and annoying up-shift light both worked. Got a good used tach off eBay, slapped it in, and it works all the time. But... the old tach had a grounding tang on it, this one didn't. I added one, and hooked it up. When the ground is connected, the temp gauge pegs. When disconnected, it gives a mid-range reading on a cold engine. With the old tach, it worked sporadically (mostly correct, sometimes would peg).
Here's the freakiest part. The mpg meter in the new tach (which was from an '84 also) doesn't work unless the lights are on! Then it immediately functions. This is independent of the grounding situation.
The gauge lights in the tach don't work unless it is grounded (no surprise).
I have been thru the manual's circuits and can't find anything that could cause this. The wiring all looks cherry, no sign of any fires or "smoke releases".
Any ideas??
Since I've rescued this car, the tach was a "some of the time" thing, then pretty much stopped. Searches brought up lots of talk about the reference and speed sensors, but both tested OK. And the mpg meter and annoying up-shift light both worked. Got a good used tach off eBay, slapped it in, and it works all the time. But... the old tach had a grounding tang on it, this one didn't. I added one, and hooked it up. When the ground is connected, the temp gauge pegs. When disconnected, it gives a mid-range reading on a cold engine. With the old tach, it worked sporadically (mostly correct, sometimes would peg).
Here's the freakiest part. The mpg meter in the new tach (which was from an '84 also) doesn't work unless the lights are on! Then it immediately functions. This is independent of the grounding situation.
The gauge lights in the tach don't work unless it is grounded (no surprise).
I have been thru the manual's circuits and can't find anything that could cause this. The wiring all looks cherry, no sign of any fires or "smoke releases".
Any ideas??
