Odd event

[Mossbeard]

Yesterday my son and I decided to take the '66 C20 out for a drive. We went about 10 miles, parked, and did some shopping. On the way home I noticed that the "Batt" indicator was pegged on the 'C' side. I thought I smelled smoke so I shut off the engine and coasted to a stop.

We popped the hood but couldn't see any sign of a problem. The alternator (or is it a generator on 66's?) was somewhat hot to the touch. I followed some of the wires off of it and felt the components looking for something that was overheating. When I touched what I found out later was the horn relay the cover popped off but it looked undamaged inside.

We started the engine with the hood up to look for problems. It started right up. The gauge was in the normal range. No smoke, so we drove it home.

This ever happen to anyone else? Any thoughts on possible causes?

My son seemed to think the smoke we smelled was from a farm house we were passing. I have to admit that it didn't smell electrical.

- M

[Mjminino]

Old gauge probably sticking?

[Clyde65]

put a VOM on it and check the charging and the cold battery voltage, you could have a dead cell.

[vince1]

Either the battery like has been stated or could it possibly be the voltage regulator (square box with 4 wire connector)? But if the battery was low it could have been a normal situation, without the smell of course. That output wire to the horn relay junction is IMO one wire size too small. Any black on the insulation close to the alternator?

If mine fails I will increase the wire size from the alternator to the horn relay and across to the battery and upgrade the alternator to a CS130 with built in regulator.

[TJ's Chevy]

The old alternator and voltage regulator went down hill on my 66 when I noticed the gauge bouncing back and forth like a disco dancer.....took a volt meter to the battery and noticed a slow discharge of my battery....so...new 100 amp internally regulated alternator took care of all that.

[ray_mcavoy]

The "BATT" gauge in these trucks is an external shunt type ammeter. The shunt is actually just the section of wire (usually red 12ga) that runs from the positive battery terminal, across the radiator support, to the junction block on the horn relay.

Under normal operating conditions, the majority of the charging system current flows through that "shunt" wire ... just like it does in a truck without gauges. Only a small fraction of the current takes the parallel path through the BATT gauge's meter movement & connecting wires.

However, a bad connection at either end of the "shunt wire" will open circuit the shunt and force all of the charging system current to flow through the meter movement, causing it to peg (it's only designed to carry about 1.5 amps maximum). In this type of "open shunt" situation, the current can get high enough to damage the meter movement and/or melt the insulation on it's 18 to 20ga wires.

I'm guessing that you experienced a momentary open circuit in the "shunt wire" that temporarily caused the gauge to peg and may have melted some of the wire insulation, giving off some smoke/fumes. Check the connections at both the horn relay junction and at the positive battery terminal to make sure they're tight and corrosion free.

To help prevent future damage to the BATT gauge & it's wiring, I would highly recommend adding a couple of 4 amp inline fuses to the gauge wiring just like GM did in the 67-72 trucks. Locate one of the fuses in the 20ga black wire with the white stripe near where it connects to the horn relay junction. Locate the other inline fuse in the 18ga black wire that runs from the starter solenoid BATT terminal up to the bulkhead connector on the firewall over near the heater box.

[Mossbeard]

Thanks everyone! Some very good advice. I'll get the battery checked out before the next outing.

Ray, thanks for the tips. I'll check for damage and buy some fuses.

Love this forum!

-M

[ray_mcavoy]

Originally Posted by Mossbeard

Ray, thanks for the tips. I'll check for damage and buy some fuses.

You're welcome! You'll also need some inline fuse holders since these trucks didn't originally have fuses in those locations. If you want the installation to look period correct, you could salvage some from a 67-72 or 73-75 GM truck with an ammeter ... they take SFE4 glass fuses and look like this:


Otherwise, some modern ATM "mini" blade fuse holders will do the trick. Something like NAPA #BK 7825332 ... these holders are rated for up to a 20 amp fuse but will accept 4 amp fuses needed to protect the BATT meter.

[Mossbeard]

Well, I think I found the problem. And raised more questions.

Clyde was correct that there was a problem with the battery. I took it to Autozone today and they said it was bad. I replaced that but it didn't solve the problem.

Today the needle began "dancing" as described by TJ. My voltage regulator had a removable cover so I looked inside and found a burned wire. I replaced the regulator and all seems normal now.

So, the questions:

Originally Posted by ray_mcavoy

The shunt is actually just the section of wire (usually red 12ga) that runs from the positive battery terminal, across the radiator support, to the junction block on the horn relay.

Ray, I'll double check tomorrow but I don't seem to have a wire running across the radiator support to the positive side of the battery. I confirmed that it is on the wiring diagram. When you added an internally regulated alternator what other changes did you have to make? You removed the external regulator? What about all of the wires that run to that regulator?


Also, I had my alternator tested today. It tested ok. However, it was so hot that I had to wrap it in a towel to carry it into the store. I had only driven about 6 blocks. I realize that it's bolted to the exhaust manifold, but is this normal? After changing the voltage regulator it still seemed to be getting very hot.

~ M

[vince1]

A hot alternator quite often indicates it is running at full charge. What do you get with a volt meter across the battery posts? When you change to an internally regulated alternator you take the connector off at the regulator (Chev) and join the two outside wires in the connector together. (brown and blue?). The brown comes from the indicator light and connected to the blue that runs to the alternator goes to terminal 1 of a 10 si or 12 si, or terminal L of a CS130 which is a much better alternator. I think if you do not have a light you could connect an ignition wire to terminal I of a CS130 but not entirely sure. Lots of stuff on the Internet about wiring a CS130. If you order one from an 89 Pontiac Safari it comes with a V pulley rather than serpentine pulley. Check them out on Rockauto for a good picture.

[vince1]

The two inside wires in the regulator connector don't get used if going to internally regulated.

[ray_mcavoy]

I agree with vince1 ... use a voltmeter to make sure the alternator isn't operating at it's max output voltage due to a stuck regulator or wiring problem.

Originally Posted by Mossbeard

Ray, I'll double check tomorrow but I don't seem to have a wire running across the radiator support to the positive side of the battery. I confirmed that it is on the wiring diagram.

That wire is mostly hidden up under the top rail of the radiator support. But you should still be able to see the ends where it comes out through the grommets and attaches to the battery & horn relay junction.

Originally Posted by Mossbeard

When you added an internally regulated alternator what other changes did you have to make? You removed the external regulator? What about all of the wires that run to that regulator?

As far as the ammeter (BATT gauge) goes, the type of alternator & voltage regulator (external vs. internal) doesn't make any difference. What is important to the ammeter is how the alternator's output wire (the one connected to the alternator's BAT stud) is connected into the rest of the system. If the routing of that wire is altered from stock (such as running it directly to the battery), the ammeter won't correctly indicate charge/discharge conditions.


There are 4 wires on the external regulator connector:

The brown wire is the field excitation / GEN light wire. The other end of this wire is connected to the ignition switch through a 10Ω resistance wire inside the cab harness. Trucks without gauges also have the GEN light connected to this circuit.

When converting to an SI alternator, you can simply extend the brown wire from the old external regulator plug to the alternator's #1 terminal.

When converting to a CS alternator, you can do the same, connecting it to the I terminal. But not all CS alternators have an I terminal so you might have to use the L terminal instead. The L terminal needs a minimum of 35Ω though so you'll have to add an additional resistor (25Ω min) since the stock wire only provides 10Ω.

The red wire on the external regulator connector is for remote voltage sensing. The other end of this wire connects to the junction block on the horn relay.

When converting to an SI alternator, this wire can be extended to the alternator's #2 terminal. Similarly, for a CS alternator, this wire can be extended to reach the S terminal.

Instead of extending the red wire, some folks simply loop a short section of wire from the alternator's BAT stud to the #2 or S voltage sensing terminal. But with that configuration, you loose the benefits of the alternator's remote voltage sensing capability. It's the same as described here for 1-wire alternators --> http://www.madelectrical.com/electri...hreewire.shtml

The white and dark blue wires on the external regulator connector originally ran to the alternator's R (relay/stator) and F (field) terminals. When converting to an internally regulated alternator, these wires can be re-purposed as extensions of the brown & red wires since they are already routed to the alternator's location. This is what's being done on alternator conversion diagrams where you see the various wires on the old external regulator connector being jumpered together.

[Mossbeard]

Ray, thanks for the detailed response. Today I checked and I do NOT have two wires coming off the + side of the battery. There's a heavy wire running to the starter and about 4 inches of wire that somebody (previous owner) cut off. I even found the empty grommet through the radiator support near the battery. What surprises me about this is How the heck does my battery charge at all?

Anyway, as soon as time permits I'll be running a new wire from the battery to the horn relay.

Vince, what would be a normal voltage to expect across the battery while at idle? I'm curious to see what the voltage is before and after replacing the missing wire.

Thanks guys,
~ M

[vince1]

I recently upgraded an alternator on an old car to a CS130 and it charges about 14.3V.

I'll check today what I get at idle on the truck. It still has the original equipment which works well.

[ray_mcavoy]

Originally Posted by Mossbeard

Ray, thanks for the detailed response. Today I checked and I do NOT have two wires coming off the + side of the battery. There's a heavy wire running to the starter and about 4 inches of wire that somebody (previous owner) cut off. I even found the empty grommet through the radiator support near the battery. What surprises me about this is How the heck does my battery charge at all?

You're welcome!

Your battery is charging through the ammeter. And when you're starting the engine, current to energize the starter solenoid and power the ignition is flowing through the ammeter as well.

Under normal conditions, the majority of that current would be flowing through the "shunt" wire and only a small fraction would be taking the parallel path through the meter movement and it's wiring. But with the shunt wire missing, it's basically forcing it to operate as a full-flow type ammeter. The coil inside the meter movement has a low enough resistance to allow that to happen. But this isn't a good situation because it's not designed to handle a lot of current on it's own without the shunt.

Had this have been a truck without factory gauges the situation would have been different. That missing wire (and no ammeter to provide a parallel path) would have cut off all power to the fuse box, ignition switch, etc. so the engine wouldn't start. And the battery wouldn't charge even if the engine was started by other means (such as jumpering the starter solenoid terminals).

The situation would have been similar with a 67+ truck that has factory fuses in the ammeter wiring. The excessive current flowing through the ammeter due to a missing or disconnected shunt wire would have blown one of those fuses to protect the meter movement & its wiring. That in turn would result in a no-start, no-charge condition until the shunt wire is replaced/repaired.

[vince1]

Mossbeard I started the truck today with -15C showing outside so it took a bit of choking to get it going. The voltage at the posts right after start up showed 17.3 settling down to 16.2 after about 15 minutes. Maybe I have a problem too. My limited understanding of the automobile electrical system is that the voltage should be regulated at around 14.0 to 14.5 no matter what the state of charge of the battery.

After you get that wire put back the way it is supposed to be as suggested by Ray what do you get for voltage?

[Mossbeard]

Originally Posted by vince1

I started the truck today with -15C showing outside

Vince, I'm so sorry that I asked you to go out in -15C weather. I'm in central California. I forget that some places get cold in the winter. I don't venture outside if it's below +15C.

I won't be able to actually install the wire until the weekend at the earliest. Because of my job, my truck and I live in different cities during the week. That's why I pester you guys with questions all week long - I'm dying to get home and play with the truck!

Anyway, thanks for the info. I'll check it this weekend and get back to you.

~M

[Mossbeard]

A new mystery.

Yesterday I replaced the missing shunt wire. The voltage measured across the battery at idle changed by about .3V (14.3 to 14.7).

I quickly discovered that the Batt gauge had stopped working. Even while cranking the starter the needle doesn't move.

So, from what I've seen on the diagrams and learned from Ray (and others), it acts like there was already a shunt wire and I've added a second! This would reduce the resistance and make almost all of the alternator current bypass the dash gauge; making it useless.

The mystery now is: where is this invisible shunt wire? If not connected to the battery terminal it must be coming through the other end of the battery cable: the starter motor!

After cutting open a taped bundle of wires I found a wire that runs from the horn relay junction toward the firewall. The wire is routed along the top of the firewall (using non-1966 zip ties, uh oh ), across the engine compartment, and into a hole in the firewall near the heater. I believe (but haven't been able to verify) that there's supposed to be a plug in this hole (Engine Harness Connector on diagrams?).

I can't tell where the wire goes after that but it must somehow be carrying current back to the starter motor then to the battery as my "invisible" shunt.

That's my best guess.

You ever feel like you'd love to look under the hood of another truck to see how the wires are supposed to look?


So, now I get to remove my heater to get to the wire (heater wasn't working anyway). I have a feeling this is about to grow out of control.

~M

[ray_mcavoy]

Originally Posted by Mossbeard

So, from what I've seen on the diagrams and learned from Ray (and others), it acts like there was already a shunt wire and I've added a second! This would reduce the resistance and make almost all of the alternator current bypass the dash gauge; making it useless. ...

After cutting open a taped bundle of wires I found a wire that runs from the horn relay junction toward the firewall. The wire is routed along the top of the firewall (using non-1966 zip ties, uh oh ), across the engine compartment, and into a hole in the firewall near the heater. I believe (but haven't been able to verify) that there's supposed to be a plug in this hole (Engine Harness Connector on diagrams?).

I can't tell where the wire goes after that but it must somehow be carrying current back to the starter motor then to the battery as my "invisible" shunt.

Yes, that definitely sounds like a previous owner re-routed the battery charging wire that serves as the ammeter shunt. And you're right, adding a second shunt wire will reduce the resistance to the point where not enough current will go through the ammeter to make it useful for measuring normal current levels.

Here's a pic with labels for all of the firewall holes --> http://67-72chevytrucks.com/vboard/s...2&postcount=91

He has 2 holes labeled "engine harness" ... the larger hole is obviously where the bulkhead connector for the harness itself goes. The smaller hole was originally used for a snap-in clip that secured the harness to the firewall.

[Mossbeard]

Thanks Ray. So, there is supposed to be a plug on the larger hole? That's disappointing but not surprising. I have a hole there with a few wires routed through. Not even a grommet to cover the sharp edges. Sigh.

I guess I'll be spending next weekend under the dash trying to figure out where everything goes.

Does anyone have experience with the commercially available wiring harnesses? If I'm missing that plug entirely (as opposed to just being shoved under the dash somewhere) I'd like to replace it.

Ideally, I'd like to get the wiring back to a near-stock state.

~M

[ray_mcavoy]

Originally Posted by Mossbeard

Thanks Ray. So, there is supposed to be a plug on the larger hole? That's disappointing but not surprising. I have a hole there with a few wires routed through. Not even a grommet to cover the sharp edges. Sigh.

You're welcome. Yes, there is supposed to be a 6-cavity bulkhead connector that fits into a rubber grommet in that larger hole.

Originally Posted by Mossbeard

Does anyone have experience with the commercially available wiring harnesses? If I'm missing that plug entirely (as opposed to just being shoved under the dash somewhere) I'd like to replace it.

Ideally, I'd like to get the wiring back to a near-stock state.

I've used harnesses made by American AutoWire and M&H ... they both make excellent products.

Since you want to return the wiring to the stock configuration, I'd recommend either M&H's reproduction harnesses or AAW's Factory Fit line of harnesses. AAW's Classic Update kits are good harnesses too but they're meant more for modified trucks and don't support the factory ammeter.

If your engine harness connector is missing entirely, you'll have to purchase both the cab harness and the engine harness. The cab harness includes the female socket and the engine harness includes the mating male plug.