328 Electrical Gremlins?

Augustine. Search for a thread of a few months ago on this problem. I had the same problem that you had and went through a lot of diagnostics which told me that the slow down ligh was not related to a bank of cylinders not firng. As a last resort I opened the connection panel in the right side of the rear trunk and sprayed electrical contact solution on the contacts after taking them apart and then I put them back together. It solved the problem and the SD light has not come on again except on startup when it is supposed to.

 

Agree with Russ, that the electrical connections on both sides of the trunk (left and right), should be cleaned up, before any further diagnosis is done. This can correct many running problems and glitches you are having. There is also a tech tip for adding an additional ground to the box in the left side. Pay particular attention to ground connections, and make sure they are clean and tight...remember, your car is now 15 years old, and this stuff needs periodic attention.

Here is a tip:
http://www.ferrariforum.net/tech/view.php?id=20

Just remember that your car has only one (1) box on the left side, not two (2) like the 308 pictured.

 

For your dash lights, you'll also probably want to check the connectors on the fuse/relay board (where the glove box would be on most cars).

As you're in Atlantic City, you'll want to clean the contacts pretty well, and might want to add some electrolitic gel (available from most auto parts stores) to keep the salt air from doing nasty things to the contacts.

When I lived in "downbeach" (some 30 years back), the headlight switch on my old Plymouth developed gremlins from the salt air. It had just enough resistance that, while it didn't show on an ohmmeter, it would heat up and pop the integrated bimetal circuit breaker. I'd be merrily cruising through the pine barrens when the headlights would suddenly go out! Tons of fun at 60 MPH.

 

The Plymouth was parked on the street in Ventnor (at a basement apartment smaller than a Ford Excursion) when I was a co-op. After graduation, I lived in Brigantine and then Somers Point.

For the relay board, you'll definately want to unplug the battery. (Hint: remove the ground lead first, in case the other end of the wrench hits something.)

For the circuit board in the rear, it depends on how steady your hand is and how much experience you have -- do you turn off the circuit breaker to change a wall outlet?

I think all the power on the rear board is fused (except for the O2 relay), but there's "hot" power on the relay board (with a lot of amps behind it). (Got arc-weld?)