13V at Coil?

From the factory the coils on older vehicles were set up with a 2-circuit power feed and there were commonly 2-3 types of coils made. The OE wiring would have a resistance wire or a ballast resistor in line with the coils feed, which was to help lower the rate of points erosion by lowering the voltage they had to switch. Normally on those vehicles that wire was bypassed when you used the starting position on the ignition. So, you had full battery power for starting then 6-9 volts while running. Now with yours being a 76 it should use a 12-volt coil and electronic ignition instead of points so it should have 12 volts at the coil and be triggered through the electronics. In the pictures it looks like there are a lot of non-stock splices. I would probably say to go through those before you replace parts, those look like unsealed butt splices and out in the weather they have a bad habit of corroding and giving odd results. Then once you are sure they are good connections try to diagnose the problem.

Do you have a Prestolite system?

It'll (usually) have a gold-colored ignition module

and your distributor will have 2 round dealees made on the front

with a vacuum post on one of them.

This system uses a coil with "INTERNAL" resistance

The 1979 and newer use a resistance wire --that system is called "Duraspark"

I have a 1977 CJ-5, I changed my Prestolite (lots of bad issues) over to a

Duraspark, everything has be great ever since.

Yours should have battery voltage at the coil!

Let's look at your backfiring issue.

Can you pin it down as to when--speed--bumps--turning L or R---RPMs?

Can you remove your breather and send some really good pics all

around and over your engine?

Do you know how to look for vacuum leaks?

Are you 100% comfortable under the hood or are you a novice?

I'm here for you!

Keep on posting.

THE MEDIC