Interesting (frustrating?) gauge cluster issues..

[Russ72C10]

How's everyone? Here's my "finding" of the day.... maybe someone can shed some light on this for me.

The printed circuit I have in my truck right now was rotten in spots, so I had to jumper in some wires to complete the circuit. works perfectly though. Dash lights are bright. But, ever since I did that, the left signal does not flash on the cluster. The right one does, but not the left. Hmmm. Also, the factory temperature gauge doesn't work... so, off I go...

I come back home with two complete gauge clusters in great condition. Printed circuits are perfect. So I remove everything from my truck to swap over one of the good printed circuits, and one of the temp gauges. One thing I notice is that apparently the printed cluster in my truck is for a TACH cluster - and there's no factory tach in it. Even better... so I thought...

I replace everything, slide the cluster back into the truck... check all grounds, etc. Well.... the brights are on by default with the new circuit. I have to kick them off by foot. Also, BOTH signal lights are on full-glow! Signals work, but both lights remain on. And, the "new" temp guage pegs itself to the Hot side. Unlike the old junk one, that goes to the cold side.

Well, I unhook it all again (getting good at this!) and put my old circuit back on. Everything works fine again.

Anyone else experience this before? One thing I've noticed is that the #1 wire (black) on the wiring harness is just hanging there, it's attached to nothing. But everything seems to work anyway. What is that black wire for?

Also, is it at all possible this truck originally had a tach dash which was swapped out - but the tach printed circuit was kept? If so, would the wiring harness be of that for a tach cluster? So it wouldn't work on a "normal" cluster?

Lots of questions..... but I'm learning... albeit slowly....

I'm sure someone here knows all the answers