Could running without a speedo cause a jumpy tach and dead battery?
 

OK, so a bit of a random one. Could running the car (1980 SC) without a speedo cause issues similar to a faulty alternator/voltage regulator?

Last week I pulled my speedo to have the odometer repaired. While it was out, I ended up going away for the weekend - about a 4hr drive up the coast. Car was absolutely fine on the way up, and driving around town on the Saturday. On Sunday, about 2hrs into the drive I noticed that the tach was occasionally swinging wildly from zero to redline, and the radio was turning itself off and then back on randomly.

Sure enough, when I eventually stopped for fuel (luckily I was only a few minutes from home at this stage), the battery was flat. Called a tow truck and had it jump started.

I replaced the battery the next day - the original was 7 years old, and figured it was probably 'due' regardless.

Unfortunately the symptoms returned today - swinging tach, and battery dead after about an hour of driving. The speedo was still out at this stage. I've now (finally) got the speedo back into the car, and the battery on a charger overnight.

Meanwhile I've been doing some reading... and the symptoms are pointing to a faulty VR and/or alternator. However, before I wade into testing and possibly repairing the alternator, I'd like to get the opinion of the forum. Is it possible that the lack of speedo could have been causing these symptoms? Bit of a long shot, I feel - and probably just coincidental that the alternator decided to die while the speedo's out, but still.... thoughts?

Al

I forget, is the alt warning light in the speedo on an sc? If so, what did you do with the blue bulb?

no. i did it for weeks while mine was being repaired.

was afraid of that... Thanks.

John, alt light is in the tach...

Just a thought, the ground jumps from the back of one gauge to the next. Is there a chance you did not maintain a ground through the instruments?

Best to check the alternator output while running the engine.

Does the alt light come on and/or stay on when turning the ignition to on and starting/running? The bulb is part of the circuit.

The light will occasionally turn on at low revs, blipping the throttle makes it go out.

If you have a volt meter, check the output at the terminals when running. Should be 13-14 volts. ....12.5 at rest, 13 ish at idle higher when revved.

Sounds like your alternator is dying but not yet dead, same symptoms as I had. Change it.

Ian