Is it the alternator.

[kdubb]

Today while pulling out of my garage, I turned on my lights,drove away, and noticed that my speedometer wasn't working. However,when I turned my headlight off, the speedometer started working again. Lights off, not working. Lights off speedometer works. What gives? I recently took out the speedo and replaced a gear inside. Could it be that I didn't connect the wires properly?

Thanks for your help!

[fbeatty]

When my alternator went out, the car drove fine for a while. Then all the electrics inside started acting up.

[86 911 Targa]

Originally Posted by kdubb

Today while pulling out of my garage, I turned on my lights,drove away, and noticed that my speedometer wasn't working. However,when I turned my headlight off, the speedometer started working again. Lights off, not working. Lights off speedometer works. What gives? I recently took out the speedo and replaced a gear inside. Could it be that I didn't connect the wires properly?

Thanks for your help!

This may/may not be your issue.


^^^^^
Prevents IC damage.

Good luck,

Gerry

[Ronnie's.930]

kdubb - to check the alternator/voltage regulator output, measure charging voltage at the battery terminals with a multimeter (with and without lights on) . . . you should see 13-14 volts at 2K RPM (sometimes might be a bit less when the engine is hot and all of the accessories are on).

[TheRedSlantnose]

Sometimes my speedometer doesn't work either, but after driving for a few miles it starts working again, but it only seems to happen during cold weather. Since it's spring and warm, it doesn't happen, but that's just my speedometer.

[DRACO A5OG]

Do what Dr Gerry wrote and also check the ground is nice and clean/solid.

[vash]

1st step is always check output with a multi-meter.

[tirwin]

Originally Posted by 86 911 Targa

Prevents IC damage.

Don't you avoid this problem altogether if you simply disconnect the negative terminal at the battery before messing with any of these connections, and then reconnecting when you're done?

[wwest]

Your speedometer case/circuit is not properly ground. Instrument light backflow is providing the needed ground.

Dash instrumentation bulb power off, low bulb filament resistance provides a ground path "backward" through the filament to other bulbs that do have ground connection.

[rick-l]

Check to make sure those two brown wires are firmly conected. The Bentley says one of those wires goes to G116, trunk floor plate left (below fuel filler tube).

Is this car in the 84-89 trange?

[rick-l]

Originally Posted by tirwin

Don't you avoid this problem altogether if you simply disconnect the negative terminal at the battery before messing with any of these connections, and then reconnecting when you're done?

The ignition switch off should do exactly the same thing.

I don't see what attaching power last really does since theoretically that is an open circuit. When connecting something up hot it is a good practice to connect ground followed by signals and then power but that is not what is done here and no one mentions the ground connection first.

[tirwin]

Rick,

My point was that if there is a risk of damaging a component because of connecting things back in the wrong order, then the safe thing to do would be to disconnect the battery. Seems to me that it would be really easy to create a short to ground with all those wires dangling around. And at least on some cars the instrument cluster is unfused. Really easy to let all the magic smoke out and it's easily avoided.

[kdubb]

I will check the connections as well as the order of reconnecting the wires and reply to this thread.

Also, thanks for the heads-up on disconnecting the battery before any electrical work is done. Sounds simple, but I did not think of that.

Kevin