Dummy Light to Gauge dash swap chaos! Help?
 

So I have a 67 c10 that has butchered wiring like you wouldn't believe. After some bad info on dash lights I fried the printed circuit from the original dummy light cluster. So, am replacing it with a gauge cluster out of a 70-72 model c10.

I've read GMC Paul's write-up, and a few million other Q&A's...

My problem is wiring of the alternator and battery to the respective #1 and #12 slots on the loom plug...

1. I have no junction block
2. This truck was in some way converted to an internally regulated alternator when the PO also did an HEI conversion

So where do I get these wires from so that my gauges read properly? Any help would be great!

Re: Dummy Light to Gauge dash swap chaos! Help?
 

You can connect one right to the terminal on the alternator. I have a single wire internally regulated alternator, so I put the wire right on the alternator lug.

The junction block is just a spot to connect into the wire that feeds the fuse block. Tap into that wire anywhere (t-tap, quick splice, etc.) and it should work.

I went from the alternator output and the junction block on my truck, and the gauge works fine.

Re: Dummy Light to Gauge dash swap chaos! Help?
 

Thanks for the quick and simple response! Everything I've been reading til now just seems to over-complicate this whole thing!

Re: Dummy Light to Gauge dash swap chaos! Help?
 

No problem. I did a lot of reading on it, and I wasn't sure if it would work or not until I tried it. But it seems to work perfectly, even with my 105 amp alternator. If I turn everything on, it will almost peg the gauge on the high side. Its almost pegged right after the truck starts when its charging the battery. With most everything off and after its been running a while, its just to the right of center. So it seems to work fine showing the amperage in the system. Makes it really easy to tell when the alternator excites (1400 rpm).

I pretty much just followed the instructions on GMC Pauls site to the letter, and tried not to let myself question anything....LOL. I start double thinking stuff like this and talk myself into not believing what others have done. My wiring was a pretty bad hack job when I started, and I have pretty much everything sorted out now. All I have to do still is connect the sensor wire for coolant temp when I get around to swapping engines. Current engine doesn't have the spot on the head for it.

Re: Dummy Light to Gauge dash swap chaos! Help?
 

Here is the way the factory wired the gauge trucks. The junction block you say you don't have is just a soldered four way connection in the harness. This may have been chopped out somewhere along the way.

You will have to have the 4 amp fuses in the wires to protect the gauge and you have to connect the wires to the alternator and to the battery but you cannot run the alternator directly to the battery or to the starter terminal. You have to have a shunt wire between the alternator and battery connections. If whoever converted your alternator ran the alternator output wire directly to the battery then the gauge won't work.

Study the diagram and you can see the connections and the shunt.

Attachment 1140698

Here is the junction on my truck which has the idiot light dash so I will have to connect the ammeter wire there. I suppose it can be connected right on the alternator as long as the alternator wire doesn't go directly to the battery.

Attachment 1140699

There is supposed to be a junction bolt on the right inner fender by the battery. This is where the fusible link from the battery and one end of the shunt wire is supposed to go. That is where the other gauge wire goes.

Re: Dummy Light to Gauge dash swap chaos! Help?
 

The junction block is not supposed to be 4 wires soldered together. The wires are supposed to have wire terminal ends o n them and then they attach to the plastic junction block mounted on the passenger side fender.
Here's a picture of the junction block that's supposed to be on all of these trucks passenger side fender near the top just under the hood about 12"-16" back from the front of fender and all wires attach to the center metal stud.
Paul @ GMCPauls

Re: Dummy Light to Gauge dash swap chaos! Help?
 

You have to make #1 & #12 wires. Run one to the alt. since you have a internally regulated alternator & run the other to the junction block shown in picture in above post, if its missing get one if you want to do it right or join the wires just before the battery positive post using whatever method you want if you want to rig it up.
Doing this the gauge then reads output at back of alt. & again just before the battery and it senses the difference thus displaying the amount of current drawn by the battery. Make sure you install the fuses inline on both wires. On a stock vehicle harness the fuses are approx. 12-14" from the alt & junction block.
Paul @ GMCPauls

Re: Dummy Light to Gauge dash swap chaos! Help?
 

You called this so right. So many try to 2nd guess things and if you just follow the basic instructions it works out, start thinking about it in depth and 2nd guessing and what's simple becomes complicated quickly because your over thinking things.
Paul @ GMCPauls

Re: Dummy Light to Gauge dash swap chaos! Help?
 

Thats the truth. And I do it to myself all the time. My day job is a mechanical engineer------which makes me an electrical idiot with just enough knowledge to confuse myself.....LOL

Re: Dummy Light to Gauge dash swap chaos! Help?
 

Not so sure thats true. I have a wire straight from my alternator to the positive post on the battery and nothing else, and the gauge works well for me. Don't know how accurate the gauge is, but it gives me the indication I expect from a working alternator.

Re: Dummy Light to Gauge dash swap chaos! Help?
 

I may have confused you with my post, but I do have the junction block you posted but the only wires that went there were the fusible link from the battery, the battery charging wire (Shunt) and the no 1 wire to the battery gauge.

The soldered junction is on the other side of the truck in the harness behind the left head light and the four wires that are soldered together are the Alternator charging wire, the voltage regulator (external) sensing wire, the other end of the battery charging wire (Shunt) and the power feed to the firewall connector for the cab.

This is how the electrical diagrams for 67 to 72 show the junction and it's how Mad Electrics website shows it. ....

http://madelectrical.com/electricalt...evymain1.shtml

The only difference is on the 66 and earlier trucks the horn relay is used as the junction block but in 67 they moved the horn relay inside the cab but kept the splice.

Attachment 1140750

here's the splice. These are in their website

Attachment 1140751

I can't see how connecting all the power wires on the right fender junction would allow the battery gauge to work because it eliminates the battery charging wire ( the Shunt) which the gauge uses to read the voltage differential between the alternator output voltage and the battery state of charge. In fact the battery gauge would see the same voltage all the time because it would be reading the voltage at the alternator and the same voltage where the alternator connects to the right fender junction.

I removed the soldered junction in my truck and added a terminal block but I kept the battery charging wire and the alternator regulator sensing wire there and connected an 8 gauge wire from the alternator output terminal to them.

On the right side I used a junction block for the other end of the battery charging wire with a maxi fuse instead of the fusible link. I'm connecting the 1 and 12 wires with fuses to each end of the battery charging wire so the gauge will be wired like the diagrams. I've also converted to the internal .
regulated alternator do I'm anxious to see how it works.

It looks sorta like this.

Attachment 1140752

Re: Dummy Light to Gauge dash swap chaos! Help?
 

You are probably seeing the discharge before the engine starts and the charge just after the alternator kicks in. the small amount of charge to the right of center would show more voltage on the alternator side or plus charge.

What happens when the truck's running and you turn on the lights and wipers? The gauge should flicker over to discharge and then return to just past center.
It's possible that the alternator feed wire is acting as the shunt and the gauge is able to read a difference between the alternator and battery voltages. The GM engineers calibrated the shunt wire by length, gauge, and resistance to correspond to the battery gauge and I would think that modifying either of those would affect the accuracy of the gauge.

In actuality the gauge has been replace by a voltmeter which is more accurate, gives better information, as well as being a lot easier to wire in and hookup.

My argument is not about how any body wires the battery gauge or whether it works or not. My argument is how the factory did it based on what I've read and seen including how my truck was set up.

Re: Dummy Light to Gauge dash swap chaos! Help?
 

I understand what you are stating in terms of "factory correct". My truck is so far from that that its not even similar at this point. But what you stated is "cannot", and that is different from saying "its not factory correct".

My point was to have an ammeter that works in the cluster, which seems to be what I have with my highly modified system.

My battery gauge will read slightly left of the center line while cranking, and will stay there until the engine rpm's exceed 1400 and the alternator excites. Then it jumps all the way right and slowly comes back down to just slightly right of center. As I turn more stuff on, it moves further right, which in mind is showing that the alternator is increasing output, as it should. If it goes the other way, the draw is exceeding output, which would mean either the alternator can't keep up or is not working. I also have a voltmeter, but its only reading what it seems in the fuse block, which can drop quite a bit when things engage. I'm slowly adding in relays to keep that from happening.

FWIW, I have a lot of added electrical load with the AC system and the dual electric fans.

Re: Dummy Light to Gauge dash swap chaos! Help?
 

It sure seems to be working and I sure won't argue with success.

Re: Dummy Light to Gauge dash swap chaos! Help?
 

Thanks for all the info guys! Honestly to do this all right I'd probably be best off re-wiring it from the ground up, but at least for the time being I need this to be a running/driving vehicle again ;) The electrical stuff can either be really simple or really complicated and I just need the most straightforward approach that lets me work with what I've got for now.

Let's just say after two dash fires and a slew of other issues, where I'm at now is light years ahead of where I was when I started! :) You guys have offered up some great info and I do appreciate the input.