No gauge readings

H

Helo pilot

New member
76 Scout II
345 v8
Holley 2300

I bought the Scout knowing the instrument panel didn't function. After reading the forum I figured I had a good grasp on what the cause was, the cvr. Built up my own 5 volt solid state regulator and no joy. Figured my electrical skills weren't what they used to be and ordered a solid state 5 volt regulator, no joy. Both times is ensured a clean 5 volt output.

I decided to check the voltage of the actual pins connecting to the pcb, no voltage. So I'm fairly certain there is a break upstream of the voltage regulator. I tried tracing wires but am having a real hard time determining what wire in the engine compartment should be sending voltage through the firewall to power the gauges.

I traced the battery cable to the starter and noticed a single yellow wire disconnected. Any chance one of the wires in this area could be causing my issues?

I should also mention this allegedly started when the previous owner replaced the ignition system.
 
Circuits 28, 28a and 28b are involved in powering the instruments. 28 is switched 12v originating from the fuse block which becomes 28a before it enters the gang connector plugged into the oil/temp pcb. The pin corresponding with 28a feeds the input side of the cvr. An average output of 5v, seen as a pulse when probed with an incandescent bulb, exits the other side of the cvr, splits to feed one terminal of both gauges, then goes back through the pcb to a pin that corresponds with circuit 28b. 28b daisy chains from that gang connector to the gang connector at the fuel/amp pcb where it ends at one terminal of the fuel gauge, thus completing the power feed to the gauges. The other side of each gauge is fed by its corresponding sender switch.
 
Two issues: circuit 28 was the one I voltage tested with no reading. Also, I can't seem to find the mythical fuse block. My service manual lists a few different places it could be (drivers or passengers side engine bay firewall). I've even checked inside the vehicle to see if it was moved. There is a box on the passengers side I have been unable to finagle open, but it appears to be way to large for a fuse block. Could the fuse block be hidden in this? I've also read a few posts stating that I May just have a handful of inline fuses. With the dead gauges the first thing I checked for was a blown fuse, but couldn't find any fuses!
 
What the heck crazy ass service manual are you using? The fuse block in an unmodified sii is found under the dash to the left of the steering column. If still present, it should be quite obvious and in plain sight. If not present...oh boy. That means some po has possibly been up to no good. Now this box that you can't get into...do you mean the glove/jockey box?
 
Interesting. That's an unusual location for a tach. I'm still curious about your manual. Is it a haynes or clymer by chance?
 
So, I went out with a flashlight (wasn't going to be able to sleep without figuring this out). Turns out it was hidden under a cb radio on the drivers side. The manual, I now realize, did a poor job of describing if it was in the engine bay or cabin (it's the original International service manual). Hopefully something is broken on this block so I can claim an easy victory.
 
Okay, that's good. We're on the same page now. The factory service manuals are the best service literature available for these piles, but do take some getting used to. The wiring schematic does provide a rough indication of where certain items are in relation to other items, but it is certainly not to any accurate scale.
 
So I checked the fuses and none were blown. I guess that's a good thing, but it doesn't help me with the gauge problems. I also checked the pins on both sets of gauges, the pcb traces, and cleaned up the terminals.

My plan was to take the entire dash off next weekend to better trace circuit 28. Do I even need to go this far, or should I be able to pick out the source in an easier fashion? I know the power has to come from the battery/ignition triggered source, but I don't know where that source goes through the firewall.

Can I just pull a 12 volt dirty source from somewhere else and directly feed the voltage regulator? Eventually I plan on replacing the entire wiring system, but just need a band aid for the time being.
 
It would be a good idea to pull the fuse panel down and check for voltage out of each fuse. The fuse holders can corrode and while the fuse is good, you'll still get an open circuit.
 
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