1970 C10 wiring

[broberson]

I'm having an issue with the wiring harness I recently purchased. I currently have the wiring set up as follows:

2 wire alternator, hooked into external regulator. Wiring from external regulator has the red wire junctioned with the positive battery terminal. The white wire is attached to the R terminal on the rear of the alternator and the blue wire from the regulator is attached to the F terminal on the rear of the alternator. I do not have the brown wire from the regulator hooked up because of overheating.

I've discovered that I have some wires crossed, but I have figured out where the DONT go. My question for everyone here is where they do go. The wire in question is from the gauge cluster, #2 spot that all the diagrams say is hooked into the brake warning light. Its two tan wires that I incorrectly had hooked into the ignition switch with a brown wire from the alternator. This is what was causing the overheating, and I have it removed.

In addition, where does the brown wire from the regulator attach to? I'm confused, so any help would be appreciated. Thanks a bunch.

[broberson]

Additional questions I've come up with..

1. What wires do I need to have going from the ignition switch. A couple of schematics show the pink ignition wire, the red battery wire, the purple starter wire, and the brown alternator accessory wire. Is that the consensus of everyone here?

2. On the gauge cluster plug, #2 has two brown wires spliced into one, and from what I've read it goes to the brake warning light. Does this need to also go to the ignition switch?

3. On the alternator, I've seen some diagrams showing a jumper from the battery post on the rear of the alternator to the F terminal, and others showing that it goes from the F terminal into the fuse panel. What is the opinion of everyone here? I may be repeating the questions I've already asked, but I'm at a loss here. I've fried my tachometer, in addition to a number of wires I've replaced trying to find the correct place to everything.

Seriously, ANY help would be greatly appreciated.

[ray_mcavoy]

It sounds like you have the red, white, and blue wires hooked up correctly.

The brown wire from the voltage regulator runs back to the bulkhead connector on the firewall behind the fuse panel. From there, it connects to a special resistance wire (brown with white stripe) that should be part of the cab/dash harness. That resistance wire then runs to the ACC terminal on the ignition switch. The resistance wire is about 10Ω and rated just a little over 6 Watts. If it's missing or damaged beyond repair, a 10Ω, 10 Watt resistor could be used as a replacement.

Trucks with a warning light cluster will also have a branch of the brown wire that runs up to cavity #8 of the instrument cluster and connects to the "GENERATOR" light. This connection to the cluster is not present in trucks with a factory gauge cluster that has a battery gauge instead of the generator light.

The tan wire that connects to cavity #2 of the instrument cluster is for the "BRAKE" warning light. It should run to a "GND" terminal on the ignition switch that momentarily grounds the wire when the switch is turned to the "start" position. That performs a "bulb check" to let the driver know the bulb isn't burned out. The other branch of the tan wire runs out to the pressure differential switch located on the distribution block near the master cylinder. If one half of the braking system (front or rear) looses pressure, it will trip the switch, grounding the wire, and illuminate the brake warning light.

Edit: I just saw your additional questions after posting my response above.

(1) Yes, that sounds correct for the list of wires connected to the ignition switch. As I described above, the brown wire for the alternator connects through a brown w/white stripe resistance wire.

(2) Yes, the tan wire from #2 on the cluster plug goes to the brake warning light. You don't absolutely need the branch going to the ignition switch but it's nice to have the "bulb check" function working as intended.

(3) The diagrams you saw with the jumper wire connected to the rear battery post and/or wires running directly from the alternator to the bulkhead connector / fuse box were likely for conversions to newer internally regulated alternators. From your original post, it sounds like you are using the original style externally regulated alternator so those diagrams would not apply to your application.

[broberson]

The brown wire from the voltage regulator runs back to the bulkhead connector on the firewall behind the fuse panel. From there, it connects to a special resistance wire (brown with white stripe) that should be part of the cab/dash harness. That resistance wire then runs to the ACC terminal on the ignition switch. The resistance wire is about 10Ω and rated just a little over 6 Watts. If it's missing or damaged beyond repair, a 10Ω, 10 Watt resistor could be used as a replacement.

The harness kit I bought from american autowire was a universal kit. In my ignorance, and first try, I purchased this not really knowing the differences until now. There are two brown wires that are labeled "alternator ignition" and "alternator switch acc". I've traced them, and the accessory comes in from the firewall to the ignition switch, and the "alternator ignition" is the one that meets the bulkhead connector, then from the fuse panel I somehow wound up putting it inline with the gauge cluster on the brake light, then on to the ignition switch. This is what I discovered was the problem, and have melted some wires.... sigh... In your opinion, what should I do with the brown "alternator ignition" wire? There isn't one with a brown and white stripe indicating the resistor needed. If I need to, I could replace it, but I'm not certain where to get one with a resistor, do you know where?

Trucks with a warning light cluster will also have a branch of the brown wire that runs up to cavity #8 of the instrument cluster and connects to the "GENERATOR" light. This connection to the cluster is not present in trucks with a factory gauge cluster that has a battery gauge instead of the generator light.

I have the gauge cluster with an ammeter gauge, brake light, and charge light. The brake light does come on when I start the truck, but I've never seen the charge light come on at all, even when the battery has been dead in the past.

The tan wire that connects to cavity #2 of the instrument cluster is for the "BRAKE" warning light. It should run to a "GND" terminal on the ignition switch that momentarily grounds the wire when the switch is turned to the "start" position. That performs a "bulb check" to let the driver know the bulb isn't burned out. The other branch of the tan wire runs out to the pressure differential switch located on the distribution block near the master cylinder. If one half of the braking system (front or rear) looses pressure, it will trip the switch, grounding the wire, and illuminate the brake warning light.

This is where I have the "alternator ignition" wire spliced in that runs to the ignition switch, but again, I've determined that the placement in the engine compartment has caused the overheating issues. This is the wire I am having problems with, and one of the main reasons for the post. The brake light does come on when I start the truck, but the battery light hasn't come on even when the battery was dead. So I'm not certain where I'm going wrong at that point.

(1) Yes, that sounds correct for the list of wires connected to the ignition switch. As I described above, the brown wire for the alternator connects through a brown w/white stripe resistance wire.

The "alternator accessory switch" wire doesn't have a white stripe, so I'm uncertain if there is a resistor inline. Where can I get one to replace it?

(2) Yes, the tan wire from #2 on the cluster plug goes to the brake warning light. You don't absolutely need the branch going to the ignition switch but it's nice to have the "bulb check" function working as intended.

I've figured out this problem from what you said earlier, so I don't think this will be a problem anymore. Thank you!!

(3) The diagrams you saw with the jumper wire connected to the rear battery post and/or wires running directly from the alternator to the bulkhead connector / fuse box were likely for conversions to newer internally regulated alternators. From your original post, it sounds like you are using the original style externally regulated alternator so those diagrams would not apply to your application.

You answered this question as well, so thanks again. With everything you've explained, I know now why everything was overheating, and also how I incidentally torched my tachometer! The brown "alternator ignition" wire was spliced into the ignition switch, the gauge cluster, and the alternator, so it was sending waaaay to much electricity into things that were already getting sufficient power!! Thanks for everything so far, Ray. Looking forward to hearing from you again.

[ray_mcavoy]

Originally Posted by broberson

The harness kit I bought from american autowire was a universal kit. In my ignorance, and first try, I purchased this not really knowing the differences until now. There are two brown wires that are labeled "alternator ignition" and "alternator switch acc". I've traced them, and the accessory comes in from the firewall to the ignition switch, and the "alternator ignition" is the one that meets the bulkhead connector, then from the fuse panel I somehow wound up putting it inline with the gauge cluster on the brake light, then on to the ignition switch. This is what I discovered was the problem, and have melted some wires.... sigh... In your opinion, what should I do with the brown "alternator ignition" wire? There isn't one with a brown and white stripe indicating the resistor needed. If I need to, I could replace it, but I'm not certain where to get one with a resistor, do you know where?

The brown "alternator ignition" wire is the one that you'll want running out through the bulkhead connector and connecting to the brown wire going to the voltage regulator.

I believe the American Autowire "factory fit" harnesses have the OE type resistance wire already incorporated into the harness. But since the universal kits are designed to work with a variety of different alternators, they likely leave adding the necessary resistor up to the installer.

Originally Posted by broberson

I have the gauge cluster with an ammeter gauge, brake light, and charge light. The brake light does come on when I start the truck, but I've never seen the charge light come on at all, even when the battery has been dead in the past.

Is the "charge" light you're referencing located in the lower right portion of the fuel gauge? If so, I think that is actually a "temp" light. And those were never hooked up & made functional in the gauge clusters. It's only present because the same fuel gauge assembly is also used in the warning light clusters.

[quote=broberson;8597814]This is where I have the "alternator ignition" wire spliced in that runs to the ignition switch, but again, I've determined that the placement in the engine compartment has caused the overheating issues. This is the wire I am having problems with, and one of the main reasons for the post. The brake light does come on when I start the truck, but the battery light hasn't come on even when the battery was dead. So I'm not certain where I'm going wrong at that point.

The "brake" light coming on when you start the truck would indicate that you have the tan wire from cavity #2 of the cluster plug correctly connected to the ignition switch. This tan wire for the "brake" light should not have any connection to the brown wire for the alternator though. And connections between these two circuits could definitely cause some problems since the tan wire is momentarily grounded when starting the truck.

Originally Posted by broberson

The "alternator accessory switch" wire doesn't have a white stripe, so I'm uncertain if there is a resistor inline. Where can I get one to replace it?

If you have a multimeter, you can use it to see if the harness does include a resistance wire or inline resistor. When measuring resistance, you'll wan to make sure the circuit is powered off to avoid false readings and potential damage to the meter (disconnecting the battery will take care of that). You'll also want at least one end of the wire disconnected to avoid false readings due to connections to other circuits (unplugging the ignition switch should take care of that). Then with the meter set to the resistance scale, connect the meter's probes to opposite ends of the wire. If it shows zero (or close) then it's just a regular wire.

If needed, a 10Ω, 10Watt resistor can be purchased from an electronics supplier such as Mouser or Digikey. Another alternative would be to wire in a small light socket that will accept a #194 bulb. That will also give you a functional charge light.

The connection would be: [voltage reg]---brown wire---[bulkhead connector]---brown wire---[resistor or charge light]---brown wire---[ignition switch ACC terminal]

[broberson]

Update:
After troubleshooting and trial and error, here’s what I was able to figure out.
1. I talked to American Autowire, the harness I got was a universal one. So some of the diagrams weren’t specific to my 1970 C10. The wire in question that key overheating was the “Aternator Ignition”. It originated from the fuse panel, and was powered by the main power wire, hence the overheating when connected inline with circuits that already had power. I removed it, taped it up, and problem solved.

2. Ray, you were correct in the wiring of the regulator-resistor-ignition. It works well. Thanks for your help, man.

3. The gauge cluster wiring #2, I corrected, going between the brake switch and the ground post on the ignition switch. The light comes on at startup, and works fine now. Again, thank you Ray.

4. Lastly, I was able to figure out that I used excess wiring length from different areas using the same colors, so this was where my confusion was coming from. I’ve since made my own wiring diagram to keep from getting confused in the future. And, I was able to figure out what happened to my tachometer. Because of the crossed wires, I fried the gauge!! I replaced it, and it works well now. Thanks again to everyone that helped.

My next project is the transmission and gearing. Im planning on a going with a 700R4 rebuilt tranny, and some new gears for the rear differential. Any suggestions for the gear ratio from anyone? I put in a 383 stroker, and I’m planning on highway driving.
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