So I'm chasing down some electrical demons.

First. The speedometer was reading erratically. Speedo would turn off and on. Also it was jumpy above 20mph.

So I replaced the VSS with a new one. The old one came out in 3 pieces.

At this point the speedo would not read at all. It sat at 0mph.

Gauge would still flash error.3

So I replaced the gauges. Now the mileage reads but speedo still dosent work.

As well as when I place the brakes and the gauges and front turn signals turn on.

I'm at a loss.

 

If your mileage reads but the speedometer doesn't work the problem is in the speedometer. The PSOM was a problem on those trucks, which is on the speedometer. So it sounds like the one you used as a replacement is the problem.

 

Both gauges did the same. Only difference is the original was erratic. Like back and forth full sweep

 

Gauge would still flash error.3

So I replaced the gauges. Now the mileage reads but speedo still dosent work.

As well as when I place the brakes and the gauges and front turn signals turn on.

What do you mean by "gauge still flash error.3" ? this is very confusing along with " As well as when I place the brakes and the gauges and front turn signals turn on"
You need to write this better nun of that makes any sense.

 

Ok,

#1.

Speedometer stays at 0mph at all times when driving. Odometer reads the mileage so the gauge is connected. At times the odometer will go blank then reads "error.3" for a proximity 30 seconds. After that the odometer will go blank, or return to reading mileage.

#2,

When the brake pedal is depressed the gauge cluster including climate control lights will luminate, as well as the front left running light.

That better?

 

Much better! when we can understand it you get a better answer
It sound like you have two problems.

Ok, #1 sound like a PSOM (programmable speedometer odometer module)
they are very common to fail on these trucks, it on the back of the speedometer, the little connector that plugs in, basically you need a new speedometer. I've done many.

#2 sounds like the brake light circuit is back feeding the park light circuit. Try putting the park lights on and see if the brake lights come on.
To fix that problem I'd start at the tail lights and trailer connector, your looking for where the 2 circuits are connected, could be a bulb, or bare wires touching.

 

I was thinking more along the lines of a bad ground(s). Check the dash grounds G200 & G201 located behind the right and left kick (cowl) panels respectively.

Not a bad idea to check/clean the ground located next to the battery as well as the one on the driver side radiator support.