Newbie needs help, replace starter now some gauges don’t work

Hi, new guy here. Just joined 2 days ago

79 GMC 3500 Sierra Grande with 350 GMC engine.
Replaced starter, now appears not charging from alternator. Checking volts at battery shows no increase with increase in revs. Lights on drops voltage with no change when rev’d.

Some gauges now don’t appear to work. Volt gauge is full left and does not move, temp gauge no movement. Oil pressure 60psi (normal) but when turn off it drops to 1/4 not zero..

The only wiring I touched was at the starter. Any ideas on what the problem could be???

I do not have an owners manual or any repair manuals or wiring diagrams. I’m definitely not an electrical expert, know just enough to be dangerous.

Thanks for any guidance.

Sounds like you forgot the alternator wire when you re hooked the battery cable on the starter.

Large starter lug should have the main battery cable and at least two smaller cables on it. The two smaller cables are the feed to the alternator BAT terminal, and the power to the junction on the firewall next to the brake booster. They both have a fusible link on the end that connects to the starter.

If your starter has been replaced, it may have an extra terminal, which is only used with points distributors (you have an HEI distributor). Make sure you did not connect something to that terminal, since it has only 9 volts when the engine is running.

Hi Good morning

Large starter lug has a large ring connector with 2 wires attached followed by the battery cable on top of it.

The new starter has 2 smaller terminals (S&R). A small wire with ring connector is attached to the S terminal. I’ll verify that it is indeed the S terminal later this morning. But it is attached to the terminal closest to the block as it was on the old starter.

Both removal of old and install of new starter was done with the battery disconnected.

So since the large terminal is hot all the time I should have 12V at one of the connections at the alternator, correct? And would it be at the 2 prong plug at the alternator? If not then perhaps fusible link is blown. What will I see and where, to know the link is blown? If I do have 12V at alternator then what?

Further on the gauges:
Oil pressure seems to be working, comes up to 60psi when started and stays there, drops to near 0 at shutdown.

Temp & volts have no movement. I found temp sender and checked it 4 Ohms cold, 202 Ohms hot so I assume it is fine.

Truck has 2 fuel tanks, one on each side. Those still work fine.

Thanks