1988 GTS speedometer issue

Pull apart and clean all the electrical connnectors with some electrical cleaner. Stabilant 22 is really good.

Try that first, if that doesnt fix it there maybe a ground issue.

 

Palo Alto Speedo

http://www.paspeedo.com/

common problem.

 

smack the top of the instrument cluster (really)

 

+1. Then consider replacing the speedo sender, screwed into the transaxle. I have owned three Ferraris, including a 328, all of them needed a new sender at some point in my ownership. If it really is the speedometer that is bad, then yes, try Palo Alto Speedometer for the repair. But I would start wtih checking connections, then replacing the sender.

 

On the 328, it is more common to have issues with the tachometer or the clock.

 

It's either the sensor or speedometer, the sensor is cheaper to replace than the speedometer is to fix. To differentiate, look for voltages at the sender unit located at the corner of the engine accessed by removing the right wheel well cover. One sensor wire comes from the fuse panel (check for battery 12V there with key on) and the other wire goes to the speedometer (check for a 6v square wave swing here with each wheel revolution). Chuck front wheels, raise the left rear wheel off the ground with the engine in neutral. Turn wheel, read voltmeter.

Elsewise throw money starting with a new sensor.

 

my 89 was like that. It would not work in the morning, and start working again at the same spot on the freeway every time. Finally died for good. A change to a used speed sender fixed the problem.

 

No need to remove the wheel well and wheel. The impulse generator is easily accessible from underneath the car.

 

Worked for me , gave the top of the instrument cluster a couple of open handed strong taps .... speedo started working again.

 

I believe that's the Ford diagnostic test!

Worked for me when I had a a dash light problem on a Ferrari. Helped me find a loose ground by pounding on the dash.