My backup lights used to work well.  Now they don't.  All fuses are good. C6 transmission. Starter safety switch works, but sometimes prevents starting while in park.  Always allows starting in neutral.  Suggestions of what to test and how to test are appreciated.

Got the AGC fuse tap and put this in with the proper radio fuse position, ran a 14 guage wire directly to the tap. This seems to have fixed my radio gremlin...now on to others
1) horn
2) backup lights
I'll post separately.

Thanks for the suggestion, guys. This sounds reasonable to me. I found that the blinker flasher is spliced on the same circuit (and the radio power is a thin yellow/black wire, not blue/red--oops), so that could be causing a big voltage drop which would affect the radio if the radio voltage was already low due to the thin wire.  NAPA has some AGC fuse taps that I'll get Monday and run a 14 gauge to the radio. I'll let you know how it goes.

69 Grande
While chasing electrical gremlins (questions 'bout that in another topic) I removed my ignition switch. It seems that the plastic part on the back which the pigtail connects to is a bit loose.  In fact, I can see inside the switch.  I'm guessing this isn't normal.  Any ideas why this would happen?  I tried pressing the tabs a little bit to make it more secure, but I don't want to absolutely break it (I think the housing is pot metal).  Suggestions, besides getting a new switch.

Funny you should mention Adam-12.  I saw an episode the other day (don't know which one) but the guys were stopped and questioning someone on the street. In the background, among others were 2 Mustangs, a convertible and a coupe.  They each drove by a couple of times.  Later in the episode, the guys were in a parking lot talking to someone. And here come the same Mustangs, driving around. No, they weren't involved in the story, just background motion.

Are you SURE that the toe-in was .24 RADIANS and not degrees.  .24 radians is  13.75 degrees and for a 25" tall tire, that's about 3" of toe!!!! (Angle (in radians) x radius of tire).  Double check the toe measurement.  If it's .24 degrees, that's about 1/19"  If it really is .24 radians, your toe is the problem. But I'd be surprised you could even drive it without leaving skid marks.

1 radian = 57.3 degrees

1/8" toe-in would be about 0.010 radians or 1/2 degree.

I'm making progress.  Thanks for everybody throwing in their expertise, too.  Lots of good tech stuff here.

I checked at O'Reilly's and they had the same Model dist. in stock, so we pulled out some allen keys and found that a 1/8" would engage the advance adjustment.  I went home and tried a 1/8"...it wouldn't even go in the hole! Tried a 7/32" and nothing....hmmm...let me try 3 mm. Because it was on a big flip-out set of keys, it wouldn't fit, so  I got over my "leave it put together" anxiety and pulled the distributor (after making many marks) and restabbed it in a better position for the vacuum hole.  The 3 mm fit and engaged something.  Oh, wait...what are my current settings.  Using a vacuum pump I tested that the advance arm immediately started moving with any vacuum at all (< 1"Hg) and was fully in at 13".  A turn CCW and it's coming in a little later.  I made several turns and got it to 5"Hg before it started advancing, and it took about 20" before full advance.  Time for a test drive.

Overall, it solved the pinging problem.  AFter a good warmup period I cruised several miles under different load conditions with no ping except for extreme acceleration at high speed.  A cruising accel from 60 to 70 was nice and smooth.  The one problem is a brief sag when starting from rest until the engine hits about 1200 rpm.  I'm idling in gear at 900.  I probably need to turn the vacuum back CW a little bit so it comes in earlier, but that's a detail adjustment now.  My big problem is solved.

Now, if I can just get the base timing down a few degrees.  I did check the timing marks this summer, and AFAICT, the 0 BTDC mark is true.  I did not have an "official" piston stop, but I did use the same technique with fine pencil marks on sticks in #1 and masking tape on the balancer .  I actually did not look at the numbers on the balancer until I was through making marks.  I was pleasantly surprised that 0 was dead center between the tape marks.

Yeah, I'm pretty sure it's either a timing issue or a temp issue.  I don't know what thermostat I have ("stock"?) but it opens, I get water flow, temp gauge is sitting in the middle.

Spark Plug is Autolite 45.  It looks normal. No deposits, slight toasty brown ceramic, gray/white electrode.

I'm running the ported vacuum, not the constant one.  I did run constant earlier but the pinging was worse.
The carb is a reman Autolite/ Cardone 30-2895 single vacuum, but I don't know if it's adjustable because I don't have any long allen wrenches.  What size? I read 3/32" somewhere, but don't know if it was for Autolite distribs. The distr is twisted such that I wouldn't be able to get a long wrench in (interference with AC compr) and I don't want to take it out until I know whether or not it has adjustable vacuum.  Can someone help with this info?

I did a warm-up drive, got the pinging problem, disconnected and plugged the (ported) vacuum hose.  The acceleration from rest was not as crisp, but seemed okay once I got rolling, and the pinging was gone.  Obviousy, I'm getting too much advance at warmed-up temps.  Is there a problem running without vacuum advance? Will it hurt (or even help) MPGs?  Why doesn't it ping while sitting still?

Thanks...

It was good to see/meet people at the BASH.

Now, back to the technical problems.  69 Grande, C6, 2.8 rear, 351 Windsor, 4 bbl Edelbrock, stock fuel pump, MSD 6A ignition, Crane Fireball E-core coil. Ford distributor with magnetic pickup. Premium gasoline

Engine cranks easily, slightly rough idle at 850 rpm when cold but idles well after warmed up.  Acceleration is good when cold throughout the throttle and speed range.  BUT once the car warms up, acceleration produces pinging/detonation/clatter at just about any speed, and also going uphill at constant speed.  When cruising at constant speed (even at 75) there is no clatter; only when I accelerate.  No unusual behavior when decelerating. No backfiring or dieseling.

Sitting in the driveway at rest, it never clatters.

Idle timing is 12 BTDC (warm, 900 rpm, no vacuum)
Idle vacuum at the manifold is 12 psi. I don't know what the cam is.
With no vacuum at the distributor, timing maxes out at 29 BTDC while adding throttle at the carb
I hooked up a vacuum pump to the distributor and pulled a vacuum without opening the throttle. As I increased the vacuum, the engine rpms increased (no, I didn't have a tach with me under the hood and no helper either) and the timing advanced. This maxed out at about 32-34 BTDC (just beyond the scale on the har. bal.) and the vacuum at the distributor was about 20 psi. Further vacuum did not give more advance or increase engine speed.

I have not tried driving the car without the vacuum connected to the distributor.

Can you help me solve the pinging without making the car driving like a slug?

Like Bob N, I'm back and forth between a motorcycle (VTX 1300) and my '69 coupe.  The gas mileage on the coupe is killing me because I'm only 4 miles from work, but I am quizzed daily about what I drove in.