66 starter / battery meter issue

[Richard E.]

I'm working on a small block 1966 roadster with a 2 speed powerglide transmission.
Often starting the car (cold or hot start) when turning the ignition switch to the start position nothing happens, except the battery meter will peg full left (-40). This is an intermittent problem, but it happens fairly often. I never hear a starter solenoid "click" when this occurs, just silence with the battery meter pegged at -40. The starter solenoid has been replaced with no improvement. If the car sits for a few minutes after the problem occurs, it will sometimes start normally with no issues. I'm thinking that the starter may have a bad winding, possibly the ignition switch is bad (seems unlikely to me), or possibly a poor firewall connection (I would not think this would cause the meter to deflect to -40 however). I have not found any loose or corroded connections thus far but possibly I'm not looking in the correct locations. If anyone has trouble shooting suggestions or has experienced this situation, I would be very interested to hear possible solutions. Thanks for all comments, suggestions.

[Stephen L.]

Re: 66 starter / battery meter issue

It sounds like a starter intermittent short. That is about the only device that would cause a -40+ amp deflection without blowing a fuse. I'd replace the starter with a rebuilt (about $75) to see if that solves your problem. You could also take your starter (if numbers correct for your car) and have it rebuilt.

[Bill B.]

Re: 66 starter / battery meter issue

I have a '70 4-spd that did the exact same thing. Replaced the starter and still had intermittent starts, hearing no solonoid (Bendix) slap and had -40A on the ammeter. Turned out for my situation to be high resistance in the clutch safety switch. Because yours is an automatic, I suspect you have a similar Neutral/Park switch that may have high resistance.

Bill B.
(Retired electrical engineer)

[Richard E.]

Re: 66 starter / battery meter issue

Gentlemen,
Thank you for the comments, I will investigate both suggestions. Regarding the safety switch, that device was removed by the previous owner, so the car currently does not have this switch. That makes the wiring suspect as to how the switch was by-passed. I'm not sure if these switches are still available for replacement on a 66, I expect they are not. I would think this switch disables the starter solenoid, but I do not have a schematic handy to check. I will do more wire tracing to see if I can find the problem before trying a new starter.
Thanks again.

[Richard M.]

Re: 66 starter / battery meter issue

The NSS plugs into 2 plastic terminal connectors in the engine harness. Both harness wires are Purple, IIRC...located just above the wiper motor under the hood gutter. If not there, somewhere nearby in the harness. The NSS wires are also purple so find those and it should get you close. It may be hard to see.

The NSS was likely bypassed by removing the NSS plugs from the above 2 mating (purple wire)plugs, then simply plugged together. This emulates the method used for manual transmissions as no NSS was used.

Check the above (bypassed) plug connection. It may be corroded, acting like a low ohms resistor causing intermittent high current operation. Also check the bulkhead connector pins. If ok, follow the purple wire down to the solenoid "S" terminal. See if it's bare and shorting to ground somewhere.

Attached is a 1966 wiring diagram. Page 2 (left center area) shows the Purple wires/plugs and how the NSS connects, along with the path down to the starter solenoid and from the bulkhead connector back to the Ign Switch on page 1.

Rich

[Bill B.]

Re: 66 starter / battery meter issue

Not to provide a tutorial here, but I'd thought I'd share a bit more about starter solenoid characteristics and why the ammeter pegs at -40A when starting when the starter's solenoid does not pull-in, but when actuating the starter with everything working correctly, the ammeter does not peg. This is an excerpt from Industrial Electronics website that explains it nicely:

When power is first applied to the coil, the amount of current drawn by the coil to begin building the magnetic field will be approximately three times the amount of current that is used after the armature moves to the middle of the coil. The figure below shows a diagram of the current flow pattern when a small solenoid coil is energized. The initial current flow is called inrush current. The current that holds the armature in the energized position is called holding current.

Since the armature physically moves inside the coil when power is applied to the coil, it will change the magnetic field, which will cause the current to drop to the holding-current level. If the armature did not move, the current would remain at the inrush level.

inrush_current_solenoid_vlv.jpg

While this example above only uses a 1.5 Amp coil current, if we assume an inrush current of approximately 50 Amp for the Corvette starter's solenoid, then using the 3:1 characteristic, once the solenoid pulls-in, the holding current, as evidenced via the ammeter, should be approx. 17 Amps, which is what I recall seeing when starting my engine.

The bottom line here is providing enough initial current to get that solenoid to pull-in. If the resistance anywhere in the circuit wiring were to get high enough to limit that initial inrush current, the solenoid will not pull in. Exaserbating the situation, copper wire resistance increases with temperature, thus if the inrush current were to remain over a period of time, the solonoid and its wiring will increase in resistance, thus creating a no-win situation in starting the engine.

Sorry for the long explanation.

[Richard E.]

Re: 66 starter / battery meter issue

Rich,
Thank you. I located the purple wires at the wiper motor easily. The connectors did not separate readily I will need to pry a bit with a small screwdriver to get them separated. I cringe a bit at separating the bulkhead connectors, but I may have too regardless. Could you please provide some correlation between the schematic of these bulkhead connectors and the actual physical connectors on the fire wall?
For the following explanation I am referring to the connections on the engine compartment side bulkhead connector not the wire harness connectors; My guess is the purple wire in question in on the "inner" fire wall connector (closest to engine), second pin down from top, on the left bank of the connector. Directly alongside the purple wire on the same connector would be a dark green wire. For additional reference I would expect the outboard bulkhead connector (closest to the driver side fender) has a dark blue wire at the top (outboard) and a yellow wire at the top (inboard). Does this sound correct? Based on this I would only need to remove the bulkhead connector closest to the engine? I hope this is not as confusing to read as it was to write! Appreciate your comments.

[Richard E.]

Re: 66 starter / battery meter issue

Bill,
Thank you for sharing this, very informative. A person should never stop learning! Appreciate your insight.

[Richard M.]

Re: 66 starter / battery meter issue

Bill, Great Info. Thank You.

Richard, Below are some photos and a wiring location note I did a while ago when I replaced a fuse panel on a '67.

Wire locations. Note it's rear view of the 2 bulkhead blocks. Top is going upward into the main harness, bottom is toward the foot dimmer switch. Purple(viol) will be "outboard", 2nd wire down.
DSCN4802.jpg

More color code reference.
DSCN4785.jpgDSCN4786.jpgDSCN4793.jpgDSCN4794.jpgDSCN4795.jpgDSCN4796.jpgDSCN4798.jpg