EmTee

Yes, I had the same reaction, but on a car like this I would also probably stick with the original configuration. One thing I would do, however, is trim that tailpipe tip to better approximate the original opening. I hate seeing cars with replacement tailpipes having the 'chop-saw' 90° cut...

A light whine may not be anything serious. Does it stop when you let-off the throttle and coast? Growling/rumbling usually goes along with bad bearings. Your noise sounds more like gear whine that is related to increased lash; likely resulting from normal wear. How many miles on the car? Eliminating the whine at this point will likely require new ring & pinion gears (i.e., a total rebuild), because resetting the lash now would change the wear pattern and most likely induce rapid wear form that point on. You may have better luck trying to find another complete third member. That would allow you to swap the entire differential assembly without hunting for individual gears and bearings. FWIW, I owned an '89 C1500 pickup that I bought with ~90K on it that had a similar light gear whine. I drove it another 100K miles before getting rid of it and the differential noise never got any worse. In fact, I know a friend who had a very nice late '80s Chevy wagon who had the rear end rebuilt (due to bad bearings) and it had a light whine following the rebuild that I don't recall was ever eliminated.

From what I have read, Code 23 is a Manifold Air Temperature (MAT) issue. Specifically, 23 says the PCM is getting a temp value pegged at the low value (-32° F). This is apparently caused by the PCM seeing the full 5V bias signal. You can try unplugging the MAT sensor and short the two pins on the connector together. If the wiring is OK, that would cause a code 25 to be set (MAT will be pegged at highest value). I'm not sure how this would cause the symptoms you're seeing unless the PCM is setting the mixture extremely rich to compensate for the cold air temperature. Before the engine dies is it belching black smoke from the exhaust?

I would do it now. It's much easier (I think) to work from above than to have to lay on the ground. Access for routing and securing the wiring will be easier too.

3800 V6 crankshaft position sensors were notorious for failing during that era. I had one quit on my '90 Bonneville. I don't think there's a good way to test it without using one of those scan tools shown above.

Search the forum, there should be several threads out there on that subject. Some of the LEDs don't work well with the dimmer.

Never seen one of these before. Between the two mentioned here, I'd have to go with the Dodge. The convertible, big motor, four-speed combination makes me go "Oooooo, Oooooo..." The quirky styling is icing on the cake!

Now the fun begins...

Weird - sounds more like a Hellcat than a Wildcat!

Ditto!

I drove the Century to get its annual safety inspection on Thursday. 'Only' about 1,100 miles driven since last year's inspection. Pretty good, but a lot less than the previous year, when I drove it ~1,100 miles on the Glidden Tour alone. She drove great, so I just checked fluids and gave it a much needed wash yesterday before finally loading it into the trailer in preparation for the trip to Buick Gardens next week...

I think GM used some type of threadlock compound on the seatbelt anchor bolts from the factory. That would explain much of your difficulty. So, are the US-spec belts not good enough to meet Australia's requirements? That seems hard to believe. Hopefully you don't need to change anything in the SRS/airbag system!

My son had a '67 Cutlass convertible with the ST300 behind a 330 4BBL. That car had good power and the switch-pitch worked well. It performed much like a later TH350.

Towpath road?

Hard to see in the picture -- is the wire intact? If so, that's good. There could still be another problem with the regulator, however. Did you perform the charging system tests outlined in the shop manual?

Better than new!

Remove the cover from the regulator and look for a fine wire tacked to the regulator base. I recently had to reattach that wire in my regulator when my alternator stopped charging.

Yes - the regulator needs to be screwed to the firewall to complete the circuit. If testing a 'loose' regulator, you need to connect a jumper wire from the regulator body to the car body (ground). The condenser is an open circuit for DC (direct current); it shunts radio frequency (RF) 'noise' on that terminal to ground.

No brown wire on Riviera, since there is no alternator light on the dash. You are correct; the condenser is for radio noise suppression.

Hmmm, Where have I seen this before...? Oh yeah, now I remember!

I believe the brown wire connects to the GEN (or ALT) light on the instrument panel. The Riviera uses an ammeter instead of a dashboard indicator light.

That's what I was thinking -- I believe that trick should work on all pre-OBD2 GM cars. The SES is illuminated, so at least that indicator appears to be working. Bear in mind that there are issues that can cause the engine to not run that don't necessarily set a code (e.g., crankshaft position sensor). https://f01.justanswer.com/nmwagschal/c2dc1097-6a35-4b83-8844-813a806098ce_p30_checking_codes.pdf

What happens when you disconnect the dimmer switch and connect a jumper wire from the common (+12V) to each terminal (high, low)? Do the lights operate? If so, either the switch is bad internally or there's a problem with the connector fitting securely on the switch terminal. It's hard to determine what's going on with the headlight switch rheostat without testing the resistor coil directly. I'd first probe the wire resistor with an Ohm meter to check for end-to-end continuity and then check continuity between the resistor and the rheostat wiper terminal. If you don't have a meter, you can also carefully probe with a test light.

Welcome - you've come to the right place!