Tach Retro install and grounds

[PbFut]

Just a cautionary post for those doing cluster work. Last summer I installed a retro tach. It was the basic kit using most all of the original cluster, replacing only the printed circuit sheet, plexi window, and adding the tach gauge mechanism. Relatively easy to do if you take your time and don’t force anything. Now to the point of my post. It’s been about 6 months and all has been fine. This past week I get this funky action with the hi beam and turn signal indicator lamps, and the cluster lamps are dead on the left and very dim on the right. My first inkling as to the cause was correct. The grounds on the left side of the circuit sheet have lost their connection. Reaching up to that area and moving the sheet some corrects the problem. To be sure this problem does not return, I’ll have to remove the cluster and do some better cleaning of the grounding contact points of the circuit sheet. Not the end of the world but I should have paid better attention to the issue when assembling the kit. Just passing this on for those who may be thinking of attacking the tachometer weekend project.

[leftybass209]

I had a similar issue, but the break in the trace was under the laminate, very hard to see.

In particular with thin traces like this printed pcb, I've noticed some that will check out okay when testing for continuity with a multimeter, but it isn't until a load is applied that the break will start to cause ground issues.

And since we're in the area, i had a buddy that thought his prop valve was giving him problems because the brake light kept a very dull glow on no matter what. It was an LED bulb that didn't shut off completely, it had the smallest draw and had he and I chasing our tails for an hour or so.

[Casper42]

I had a similar issue with a reproduction kit. I flip the turn indicator and 1/2 the dash lights would dim in conjunction with each flash. I then simply added an easy ground wire to the back of the housing, one of the case screws, not a screw to anything taking power - then ran the wire to just the dash metal. Issue cured.

[PbFut]

After removal and check out it was in fact the sheet metal screw on one the speedometer side of cluster that was not fully grounding. Reseating the screw was all that was needed. For reference, the sheet metal screw that holds the printed circuit on the fuel guage side of the cluster is the connection for the cluster metal housing and the ground in the cluster harness and part of the printed circuit sheet. The other half of the sheet ground circuit is grounded using the attaching sheet metal screw on the cluster metal housing close to the fuel guage. Loosing that ground circuit was the issue and created back feed and the crazy lit indicators. I corrected the oem grounds. All is good. I also ran secondary wire using crimp on loops at the 2 ground screws and grounded the added wire to the dash. This will eliminate any future failure due to corrosion on 50 year old screws. Cluster now works as before. With maybe a bit of plesebo effect seeming brighter than before all this happened.