I have a good ol' '79 F250 highboy with transplanted '71 429 and C6 tranny. I have had it about seven years now and have had numerous electrical issues. The horn shorted out, alt stopped working, had shorts here and there. So I finally fixed most of the issues by replacing the crumbling plastic instrument cluster mounting plate. Oddly enough this fixed an ongoing battle with getting the alternator to charge and some of the other issues.

So I also replaced the printed circuit (brand new) for the instrument cluster thinking that this would fix some of the instrument issues as well as the dash illumination lights, which don't come on (still except with the turn signals).

I can't come up with what would cause all the right side lights and indicators to come on with the right turn signal and vis versa with the left signal, but that seems to be what it wants to do.

Anybody have any ideas?

 

It could be the wrong IP PCB. Especially if your wiring isn't very hacked up.

 

I am honestly not familiar with those acronyms, but I assume that means Instrument Panel (IP) Printed Control Board (PCB)? In other words, what I referred to as the 'printed circuit'.

I am fairly confident the one I have is correct. It matches the old one perfectly with the other options (from LMC Truck) being very different.

If it is the same the panel lights and signals all worked correctly before the electronic issues, that seemed to be related to the mounting plate falling apart.

I am wondering if it could be a loose connection or wire in the harness to the board or something

 

TWO different printed circuit boards, TWO different instrument cluster backs. The difference: With Oil/Amp GAUGES or with Oil/Amp WARNING LAMPS.

D6TZ-10K843-B .. Printed Circuit Board-Use with Oil/Amp GAUGES / Marked: D6TF-10C956-BA / Obsolete

1976/79 F100/350; 1976/91 Econoline; 1978/79 Bronco.
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D9TZ-10K843-A .. Printed Circuit Board-Use with Oil/Amp WARNING LAMPS / Marked: D9TF-10C956-AA / Obsolete

1979 F100/350 & Bronco; 1979/86 Econoline.

 

Yes, it is the D9TZ-10K843-A - the same unit as I had before. It is the correct unit.

 

Could be. The floppy PCB ccould've moved around a little, especially where it curves down into the cluster back, where the electrical harness plugs in.

If it's a swapped in engine, verify that you have a ground strap wire from the engine block to the firewall. If that's missing it can cause all kinds of unexplainable weirdness. And I suspect that it can overburden the ground pin/wire at the rag-joint, rendering the horn inoperable once that ground burns open.
I believe there's also a ground behind the cluster, maybe to the steering column support?

But I agree, assuming no other changes at the time, the new parts should go in and perform at least as good as the old ones did.

 

Be aware that the instrument cluster back is different with Oil/Amp GAUGES vs Oil/Amp Warning Lamps.

 

Yes, I know. The replacement backing and circuit exactly match the original and would not fit my instruments and gauges.