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So after searching the forum there are 100's of posts about the instrument cluster failures, none of them seem to match ALL of my symptoms. Here's what's going on:
- Odo is dark/dead (no light or digits at all)
- Tach sits at 0, with no needle motion. (car running & driving)
- Speedo sits at 0, with no needle motion. (car running & driving)
- Oil pressure & coolant temp gauges are both pegged at max end of their respective scales
- Fuel level gauge appears work normally, at least it's showing about the same level since I last drove the car - haven't burned enough fuel yet to really say if it's working though, or if it's just stuck at its last position.
Now since I just completed a minor re-wire job on my Link ECU, I figured that MIGHT be where something went wrong with the cluster but I don't see how.... The re-wire job involved just few I/O pin assignment changes on the ECU end; these were simple pin swaps on the AMP Superseal connectors & DTM connectors that I was able to 100% bench test, and functionally test all the ECU's I/O powered up in test mode - everything works (except my cluster as noted above) and the car runs & drives just fine. One other point to add - since the Link provides the tach signal to the cluster, it should have done it's usual power up sweep when keying on (i.e., a slow sweep from 0 to redline and then back to zero), and that didn't happen either.
I have a cluster like that. speedo and tach dead. It's the speedo that's the culprit. Tach worked when put in another cluster. In this particular speedo I replaced most of the capacitors. The real problem was C3 the large capacitor. It corrodes the trace just to the bottom of it when it leaks. In my case it also did damage to DA1(which has only a single Chinese source on ebay). You have to bridge the trace with a wire between the via and ZD5. Anyways that exercise brought back the speedo odometer and tach but the speedo needle is still dead. The odometer now does work and increment. I had no help here so I just left it for now. I'm not an electronics guy so changing out components only goes so far without some direction on what to look at next. Some suspects can be the drive motor or one of the chips or another bad trace(I looked closely but I may have missed it). I'm sure you found the long thread thread on repairing the odometer/speedo here(it has the components and sources to purchase them).Hope this helps give you an idea of what you are up against.
Problem solved - I found a miswire error in my harness!
So my problem is solved. I decided to pull out my Link ECU harness again and do a pin-by-pin continuity verification of every circuit on it it against my schematic. As it turns out, I somehow made a mistake and reversed the wiring between digital input #2, which connects to the clutch switch and AUX output #3, which drives the tach. What that meant electrically is that instead of seeing a PWM square wave signal to drive the tach akin to how the OEM ECU would drive it, instead the cluster's tach input was seeing a steady +12VDC (via a the pull up resistor, which is how I had the clutch switch input configured in the Link). This apparently powered down the whole thing.
Anyway, after fixing the wiring error and reinstalling everything, all gauges, speedo, tach & odo are all back to normal. Just glad I didn't fry anything!
Spoke to soon, but the problem is SOLVED, courtesy of Michael Gagne'!
Well after fixing my wiring mishap and actually test driving the car, the problem returned - but only with the engine running! As I was stumped at this point, I reached out to FD cluster guru & repair expert Michael Gagne on Facebook, figuring I'd have to ship my cluster out to him for a restoration job. After a brief phone/txt consultation where we discussed all the symptoms I was observing and how my Link ECU was obtaining it's speedo input, before & after the wiring mods, he informed me this is an easy fix that involves adding a single ground wire to the cluster! Reference the cluster photo below, I simply had to add a ground wire between the chassis and the cluster's ground terminal screw, circled in blue. Basically just a ring terminal sized for the small screw, some 16 AWG wire I had handy, with another ring terminal bolted to the dash metal support bar underneath.
And here's why my cluster went wacky - In my "before" wiring, I had tapped the vehicle speed sensor (VSS), so my Link ECU and dash cluster can share the VSS input. Since the VSS is a 2 wire VR type sensor which is wired to the factory cluster in a floating ground mode (i.e, neither of the 2 terminals are connected to ground) but the Link ECU digital inputs are setup for 1 wire sensors to use a common chassis ground or dedicated ECU sensor ground, I connected the (-) terminal of the VSS sensor to the Link's sensor ground. It was this ground that provided a ground return path for the dash cluster, which was otherwise eliminated when my FD went aftermarket ECU because cluster's ground circuit on a stock FD is normally routed thru the emissions harness, among a few others. My "after" wiring eliminated this path, because instead of tapping the VSS directly, I instead tapped the cluster speedo output (TTL square wave, 4 pulses per rotation of the VSS sensor) that is routed thru to the OEM front harness on a G/R wire on the B1-01 connector (OEM ECU), which I piped into my Link ECU's digital input. So now since I'm no longer dealing with tapping a 2 wire sensor, that added ground was no longer there, hence the problem. As Michael explained to me, the "tell" here was the fact that both the coolant & oil pressure gauges were pegged at max with the engine running, because that is the path of least resistance for the speedo/tach/odo circuits to return to ground.
12-01-23, 04:59 PM
