Voltage issue - Gauge Cluster and wiring Questions

[greywurm]

Hey guys, eletrical issue... '71 c10 with '68 I6 TH350 (and '68 front end - i think PO wanted to make it a 68). Had the truck about a month, just going though the issues and getting her running properly.

I got tired of having to jump start the truck every other time i wanted to troubleshoot a tranny issue, so I changed projects and have been trying to figure out why she is slowly using volts. Battery will be just over 12 volts whenthe truck is off, but once she starts up it will drop below 12 volts and I can watch it lose .01 volts every 1-2 minutes. Turn the headlights on and it drops much much faster. And the headlights barely light anything up (Only drove at night once and it wasnt fun driving in the dark with dim lights on california windy mountain roads).

I've replaced the alternator, voltage regulator, ignition switch and had the battery tested (only 6 months old). The battery cables look to have been replaced shortly before I got the truck. The starter is also new if that matters. I added some grounds straps and reconnected the ones that werent reconnected after the PO swapped the v8 to the i6. I now have 1 from the chassis to block, 2 from firewall to block, 1 from chassis to battery, 1 from chassis to wheel well, 1 from chassis to cab and one from chassis to bed (last three underneath truck). I used this post to get ground strap info. Hell, I even have added a ground from the bolt that ground the regulator to the alternator.

I came at a loss of what else to do so I started tracing wires to see how everything is wired up and studying wiring diagrams. I have found some oddities that I need to investigate further, but I have some concern over my gauge cluster and its circuit board. The one time I drove at night, I noticed that the gauges didnt light up when i turned the headlights on - just added it to the list of things to check out. However, when I pull the cluster out to get a better look at the wiring, i noticed that the metal connect for the last pin (for ground according to the diagrams) was snapped off. I made an attempt at soldering some metal from a broken fuse to replace that but it didnt seem to help.

Some other related things is that the voltage meter and temperature gauge in the cluster do not work. there is an aftermarket temp gauge that does work, however I want to go back to the stock one, i just dont know if it is broken or not. The voltage needle never moves whether the truck is running, dying, or off. Also the speedo gets wirey when on the highway. The parking brake warning light is not hooked up, but is not in the cluster. Should it be?

Is there any way to salvage the cluster and circuit board or should I look into replacements? I found that i can get the printed circuit for about $50 new and have found used gauge clusters locally for $150, but who knows what does and doesnt work.

Any other ideas on where to look for the voltage loss before I start cutting up the wiring job the PO did? Which electrical system should I focus on? It seems to me that there are wiring mistakes in the ignition switch, starter, fuse panel and charging system. For example, it currently seems like the red wires from the battery, regulator, alternator, ignition and a fused black/white are all soldered together near the regulator, but I need to do some double checking on each wire.

I attached pics of the cluster with close ups of my poor solder job and the temp and voltage gauges. I have larger size pics if helps?
Thanks everyone

back of cluster


front of cluster


close up of attempt to fix broken piece


temp guage


battery gauge - plastic on right post is flayed but i think the connection is still safe


parking brake warning light and the cable that comes out of it. other wiring going into it comes from the brake sensor. not sure where this goes yet.

[TheOtherScott]

Wow! I feel for you! I'm certainly not as good as many here but my $.02 worth: I know you said you had the battery checked but did they do a load test? I had one about that old that failed...

If you do have a voltage leak sometimes you can start pulling fuses, one at a time, and see if your leak stops. If it does you know what circuit to concentrate on.

Good luck!

[greywurm]

Thanks for the reply. I started with fuses. Pulled every single one and no change on the voltage. In my preliminary trace, i recall at least the red wire in the unfused ign goes nowhere as well.

I also just found that there is a solder join of some other wires. im writing everything down right now so i can diagram how it currently is set up.

here is a pic of the spliced red and brown wires. the red goes from the battery to the regulator, alternator into the cab to another solder joint that splits to the head light switch and the ignition.

[FirstOwner69]

First, welcome to the forum!

Second, I'm no expert on wiring, but I'll try to answer some of your questions.

- I wouldn't give up on the gauges until you replace the printed circuit and get everything else in good order.

- The battery gauge is not a volt meter. It's an ammeter that should normally be slightly to the right or left of center. Left is discharging. Right is charging. The needle position doesn't vary much. If it's not working at all, there is a fuse holder near each headlight. Each fuse holder contains a short 4 amp fuse (fuse holder is shown at the top of the picture below). One or both fuses may be blown.

- The soldered wires (shown at the bottom of the picture below) are part of the factory harness.

- The factory temperature gauge is fed by a dark green wire that connects to a sending unit on the engine. I don't know where the sender is on an I6. On a small block it's in the left head. It's possible that the aftermarket gauge is utilizing this wire but probably not the factory sending unit. However, the aftermarket sending unit may be in the factory location. Obviously, the factory gauge would not work in this scenario.

- I've never heard of a parking brake warning light in these trucks. There is a warning light which warns of a malfunction in the hydraulic brake system. It's fed by a tan wire that attaches to the brake proportioning valve on 71s/72s or distribution block on 67s-70s and runs to the cluster plug which feeds the brake light on the fuel gauge via the printed circuit.

- I don't know what you mean by the "the speedo gets wirey when on the highway". The speedo is mechanical and is driven by a cable to the transmission. It will bounce if it needs lubrication or if it's kinked. Back in the day they recommended powered graphite for lubrication.

[greywurm]

Originally Posted by FirstOwner69

- I wouldn't give up on the gauges until you replace the printed circuit and get everything else in good order.

After comparing my notes of how its wired and the wiring diagrams, my initial thought of bad wiring isn't as suspect as I thought. Those solder jobs I guess are factory. There are some other oddities, but that shouldnt matter. for example, the purple wire out of the ignition switch is a new one, then it gets spliced with the original and both go to the starter. I am going to order a new printed circuit and go from there.

Originally Posted by FirstOwner69

- The battery gauge is not a volt meter. It's an ammeter that should normally be slightly to the right or left of center. Left is discharging. Right is charging. The needle position doesn't vary much. If it's not working at all, there is a fuse holder near each headlight. Each fuse holder contains a short 4 amp fuse (fuse holder is shown at the top of the picture below). One or both fuses may be blown.

OK. I might need to find a diagram for the fused wires. Are those the black/white striped fused wires? Both fuses were blown, I replaced them, but im not sure where to hook up the end thats near the passenger headlight/battery. I touched it to a positive lead and it threw sparks, but I wouldnt expect a ground wire to take fuses.
I also read on another thread that the ammeters go bad and can cause a lot of electrical issues. The poster suggested upgrading to a voltage meter. Any idea if that is worth the trouble? Also, I guess the needle should stay put if the cluster is removed?

Originally Posted by FirstOwner69

- The soldered wires (shown at the bottom of the picture below) are part of the factory harness.

I saw that in diagram after I posted. Thanks. I now know this is not the issues

Originally Posted by FirstOwner69

- The factory temperature gauge is fed by a dark green wire that connects to a sending unit on the engine. I don't know where the sender is on an I6. On a small block it's in the left head. It's possible that the aftermarket gauge is utilizing this wire but probably not the factory sending unit. However, the aftermarket sending unit may be in the factory location. Obviously, the factory gauge would not work in this scenario.

The sending unit is at the front of the block. It has a wire with an exposed ground wire coiled around it (i know because I accidentally brushed the red wire from the alternator against it) going straight to the aftermarket gauge. The gauge is nice, but it is just tied to the dash with a string, so I'd rather take it back to factory. I guess i need to see where to put the wire from the sending unit to check if the factory gauge actually works.

Originally Posted by FirstOwner69

- I've never heard of a parking brake warning light in these trucks. There is a warning light which warns of a malfunction in the hydraulic brake system. It's fed by a tan wire that attaches to the brake proportioning valve on 71s/72s or distribution block on 67s-70s and runs to the cluster plug which feeds the brake light on the fuel gauge via the printed circuit.

The red light in the last picture of my first post is wired to a parking brake sensor. It looks like it was added - the gauge cluster looks to have been drilled out to allow this light. I just havent found where to hook up the second wire to complete the circuit.

Originally Posted by FirstOwner69

- I don't know what you mean by the "the speedo gets wirey when on the highway". The speedo is mechanical and is driven by a cable to the transmission. It will bounce if it needs lubrication or if it's kinked. Back in the day they recommended powered graphite for lubrication.

It jumps around alot. I think the gear in the cable might be worn. I know its not original, because there are two. The original is still there just not hooked up. The end at the gauge looks like it has some damage to it. But I'm not sure.

[FirstOwner69]

The black and white fused wire is positive. The end near the right headlight goes to the junction block on the right fender adjacent to the battery. There should be a loop on the end to go on the stud. The other end is the black and white wire included with the red wires in the soldered wire connection in the pictures. I believe I read in another thread that this wire is basically a shunt that measures current drop/rise causing the gauge needle to move. I'm not sure why it would spark unless the wire has a bare spot that is grounding. If you want original appearance, I'd stay with the ammeter. Most people do feel the volt meter gives more relevant information.

The correct temperature sending unit for the factory gauge is probably not the one for the aftermarket gauge. If you can post a picture of the one you have, we can get a good idea of what you are dealing with. I have no idea why there would be a wire coiled around it.

The speedo jumping around may be fixed by lubing the cable. I'd try that before getting a new gear. In addition to a cable kink or need for lubrication it could also be caused by use of a lubricant that has dried out causing the cable to momentarily bind as it rotates. You said, "I know its not original, because there are two. The original is still there just not hooked up." I'm not sure I understand what you are describing.

[greywurm]

Originally Posted by FirstOwner69

The black and white fused wire is positive. The end near the right headlight goes to the junction block on the right fender adjacent to the battery. There should be a loop on the end to go on the stud. The other end is the black and white wire included with the red wires in the soldered wire connection in the pictures. I believe I read in another thread that this wire is basically a shunt that measures current drop/rise causing the gauge needle to move. I'm not sure why it would spark unless the wire has a bare spot that is grounding. If you want original appearance, I'd stay with the ammeter. Most people do feel the volt meter gives more relevant information.

This is the fused black wire. It's actually a separate wire than the black/white fused wire that is in the main splice of red wires for the battery/alt/regulator.

Originally Posted by FirstOwner69

The correct temperature sending unit for the factory gauge is probably not the one for the aftermarket gauge. If you can post a picture of the one you have, we can get a good idea of what you are dealing with. I have no idea why there would be a wire coiled around it.

Here's a pic of the sending unit and back of gauge

Originally Posted by FirstOwner69

The speedo jumping around may be fixed by lubing the cable. I'd try that before getting a new gear. In addition to a cable kink or need for lubrication it could also be caused by use of a lubricant that has dried out causing the cable to momentarily bind as it rotates. You said, "I know its not original, because there are two. The original is still there just not hooked up." I'm not sure I understand what you are describing.

There are two cables... My fingers are touching both at the firewall. One is not connected to anything, transmission nor speedo, but is still in the mounting brackets. The one that is connected isnt mounted anywhere. So this tells me someone added a second cable for some reason.


Here is the black to red wire I was talking about

[greywurm]

Where does the unfused ignition wires go from the fuse panel? The left one is black, has an inline fuse and then is spliced to a red wire. The other end of the red wire goes nowhere. Its cut and taped off.
The right wire is pink. It looks like it runs behind what's left of the A/c.

[truckdude239]

Okay i u der stand your trouble shooting but have you verifyed that it is charging.? Should have 14-14.5 volts running if its not start with the charging system. Worst case is its time fore a rewire

[greywurm]

Originally Posted by truckdude239

Okay i u der stand your trouble shooting but have you verifyed that it is charging.? Should have 14-14.5 volts running if its not start with the charging system. Worst case is its time fore a rewire

Thats part of the problem. I'm not getting even 12 volts when running. I've replaced the alternator, regulator, load tested the battery twice now, added ground straps, tried a new ignition, pulled all of the fuses then replaced a few that I broke taking them out, etc. I'm not sure what else to do with the charging system other than swap out to a larger internally regulated alternator and hope that corrects everything.

[FirstOwner69]

The temperature sending unit is definitely not the factory unit.

I don't see the speedo cable in any of the pictures.

We are beyond my scope of knowledge electrically. I sent a PM to VetteVet to see if he'll chime in on this discussion. He's our resident electrical expert. In the meantime here is a link to a color coded wiring diagram in case you haven't seen it.

http://67-72chevytrucks.com/vboard/s...d.php?t=185856

[greywurm]

Oops. Didnt post the speedo cable pic. Also resized the temp gauge pic.
Thanks for all your help!

I am pulling the new alternator now and am going to have it tested. I might try to return it and grab an internally regulated one. Any preference on which model to grab one from? I've read that an 84 trans am or a 86 c10 are the way to go.

Speedo cables:

[FRANKENSTEINC10]

Welcome Greywurm. I was having the same problem with my voltage a while back during my engine swap. I realized after swapping another alternator in that I never ran the power wire to the back of the alternator. Check and make sure it's there before you tear into something you don't have to.

[greywurm]

The red cable to the alternator? It is connected to the correct post.

[VetteVet]

See if this helps , there's a lot of information but you have a lot of issues. I have to go away but ill check back later. You are getting a lot of good info from the guys.
...........
http://67-72chevytrucks.com/vboard/s...d.php?t=417872

[davepl]

I'd get the alternator checked. Maybe you have a shorted diode. Does it get hot when it runs, even though there's not a lot of load?

[greywurm]

Originally Posted by davepl

I'd get the alternator checked. Maybe you have a shorted diode. Does it get hot when it runs, even though there's not a lot of load?

I got back from picking up the battery about a half hour ago - got it charged and load tested again just to be safe. I also brought the new alternator with me and tested it as well.

The alternator averaged 14.69 volts. Low 13.7, High 15.7

I just took off all the electrical tape that was wrapped around the four wires for the alternator and found some suspect issues. I'm not sure if this would really cause my voltage issue, but doesnt look good. You can see the red and black cables are melted like they were resting on the block and the blue and white wires are twisted to the harness plug. at least they were wrapped in tape individually. I'm going to crimp those and cut the red and black wires down past the melted insulation.

[greywurm]

I have a dark green wire by the driver's side head light that isn't hooked up. Any idea what it is for? Looking at the wiring diagram, it looks like it might be high beams?

[FirstOwner69]

Originally Posted by greywurm

I have a dark green wire by the driver's side head light that isn't hooked up. Any idea what it is for? Looking at the wiring diagram, it looks like it might be high beams?

That one looks like the horn wire. Does your horn work? Do you have 1 or 2 horns?

[greywurm]

Originally Posted by FirstOwner69

That one looks like the horn wire. Does your horn work? Do you have 1 or 2 horns?

2 horns. They work. There is another dark green wire going the first horn. I'm guessing it's been bypassed...

I'm starting to wonder if I should just order a new harness.

[FRANKENSTEINC10]

Well the alternator sounds good. Not sure how your truck is set up but on mine I have 2 wires coming from the main harness (near the horn/ drivers side headlight) to the alternator. On of the wires plugs into a male spade connector and the other has a ring that goes to the back of the alternator. From the battery there is a wire that connects to the other male spade connector, and a large zero gauge cable that goes to the bolt in the back. The large wire is what feeds the current from the alt to the battery.

[greywurm]

So I got everything hooked back up. Replaced all of the twisted splices with butt connectors and cut the alternator wires back behind the melted areas. Added the black fused wire near the passenger side headlight to the junction for the positive terminal of the battery.

Voltage at the battery when off is 12.35 volts, same at alternator.
At the battery while running, 12.14
At the posts on the alternator, 12.04. I am touching the leadsto the black and red posts
When I turn the headlights on, it drops 11.97 at the battery and 11.71 at the alternator.
I am still experiencing .01 volts dropping every 30 seconds to a minute or so at idle.

Anything else I can do to troubleshoot?
I am done messing with it for the day.

[FirstOwner69]

Originally Posted by greywurm

So I got everything hooked back up. Replaced all of the twisted splices with butt connectors and cut the alternator wires back behind the melted areas. Added the black fused wire near the passenger side headlight to the junction for the positive terminal of the battery.

Voltage at the battery when off is 12.35 volts, same at alternator.
At the battery while running, 12.14
At the posts on the alternator, 12.04. I am touching the leadsto the black and red posts
When I turn the headlights on, it drops 11.97 at the battery and 11.71 at the alternator.
I am still experiencing .01 volts dropping every 30 seconds to a minute or so at idle.

Anything else I can do to troubleshoot?
I am done messing with it for the day.

You mentioned that you also replaced the voltage regulator. I'm starting to wonder if it or its wiring is defective. If defective, it could explain these symptoms. From one of your first pictures, it appears to be a newer type solid state unit. I seem to remember a thread a couple years ago where someone had a slow voltage drain with one of these such as you've described.

[greywurm]

Originally Posted by FirstOwner69

You mentioned that you also replaced the voltage regulator. I'm starting to wonder if it or its wiring is defective. If defective, it could explain these symptoms. From one of your first pictures, it appears to be a newer type solid state unit. I seem to remember a thread a couple years ago where someone had a slow voltage drain with one of these such as you've described.

It is a solid state regulator. The one I replaced was also solid state.

Are you referring to the wiring in the harness that attaches to the regulator? Just for kicks, I picked up another regulator, but haven't installed it yet. I haven't been confident that the wiring is correct so I am worried that perhaps I am shorting out the regulator.

[FirstOwner69]

The wiring between the regulator and alternator.