General Electrical/Power issue.

[Terrinharmon]

I recently bought a 1978 fiat spider 1800. The old guy we bought it from kept it in good condition, but that means everything is original so I have been replacing certain things and it is running way better, the problem I'm having is the brake light and the seat belt light and radio don't turn on until it hits around 500rpm, and while I'm driving if I hit around 4000 rpm in 4th gear the car sputters, but runs fine under that. I have replaced the alternator, carburetor, starter, battery and distributor. The distributor is in timing with the spec on the manual and the idle is set 900rpm which the manual recommends. I'm just at a loss is all.

 

[348azeus]

On the electrics sounds like you have too much resistance in the circuits. I would check connection like making the earths good, cleaning fuse connections and block connectors. You may find using something like de-solv-it will help.
The running sounds like a blocked jet, but you may have a fuel delivery issue with the pump or fuel lines ? Try and blow through from tank to carb and fit an in-line filter. Without seeing it misbehaving it’s always difficult but it could be age related and coil or plug leads could be breaking down.

 

[Terrinharmon]

I replaced the manual fuel pump and I tuned the carb to spec, but I'm new to carbs so I don't know the full tuning about it. Do you know if the ground is under the car like some cars or is there spot in the engine bay?

 

[s130]

I don't have a 124 but generally Fiats of that era have from the battery terminal a strap/lead to the chassis under the battery box on the inner wing in the engine bay and this then continues to the engine block/gearbox. Often dirt and corrosion affects the connection under the battery box/to the chassis.

 

[348azeus]

Depending on the model some have a group of earth connections on the inner wing sections or even the bulkhead.