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.

[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.

[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.

[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