Electronic/Charging Malfunction

[volvoaddict007]

1990 760 Turbo Wagon. 304K miles. 2.3 liter.

I jumped my 95 Nissan 300ZX last night with my 760 after the ZX was sitting for a week. The ZX would not start with the jump after being very dependable for the last couple of years since I bought it. I was sure I had the correct terminals hooked up although I may have touched the cables together briefly at some point prior to hooking up.

Then the 760 would not start like it had a dead battery so I charged the battery with a trickle charger for about 6 hours and it ran OK till the headlights ran the battery down so it definitely is not charging itself. Now all the dummy lights are lit up on the 760 instrument panel and the car is acting like the alternator is fried. The headlights are draining the battery rapidly. I had the alternator rebuilt about a year ago.

What is shorting or ? to cause all the dummy lights to stay on when driving the 760? Could a short in the battery or alternator cause this?

[billofdurham]

When jump starting any car you should follow a set procedure to avoid possible damage to either or both cars.

1. Turn both cars' ignition off.
2. Connect one end of the red wire to the positive of the bad car battery.
3. Connect the other end of the red wire to the positive of the good battery.
4. Connect one end of the black wire to the negative of the good battery.
5. Connect the other end of the black wire to an engine earth (ground) point on the car with the bad battery. One of the engine lift hooks is a good point. Do not connect it to the negative terminal of the bad battery as the bad battery may be putting out hydrogen which could explode if a spark occurs near it.
6. Start the good car engine.
7. Start the bad car engine.
8. Switch on the headlights of both cars. This is to prevent a spike after you remove the cables since the regulator was set to supply a heavy load. You instantly switched from a heavy to light load and the voltage may spike.
9. Disconnect the jump leads in reverse order, being extra careful to keep cables and clamps from touching as a short circuit can cause damage.

The alternator (charging) warning light in the instrument cluster feeds a small amount of electrical current to the field coils in the alternator when you turn the key on and the engine isn't turning. This excites the coils, which are an electromagnet, and the alternator gets the magnetic field it needs to start charging as soon as the engine runs. When the alternator isn't charging at all (engine stopped) that wire to the alternator also provides an earth path for the warning bulbs in the cluster, so they light up. Diodes in the network keep current from back-feeding into unwanted circuits.

Having all the idiot lights go on at once is not as strange as it might seem. This will happen if the small wire leading to the back of the alternator is earthed. It will also happen if the alternator is not generating any current. When this wire is at earth potential, it is the same condition as before you start the car - hence the idiot lights are on.

First check the wire at the back of the alternator but, if you did inadvertently touch the cables together, you may have done internal damage to the alternator.

Bill.

[volvoaddict007]

Thanks Bill.

You have always been very helpful with this car for the last 7+ years that I've owned it. It has been a great work vehicle for me and very dependable.

It sounds like a damaged alternator is the worst case scenario. I'm not good at all with electrical stuff. I will have it checked out and take a look at the wire AND properly jump cars in the future per your instructions.

[volvoaddict007]

Turns out that somehow the alternator belt had broken during the jump... complete mystery.

Anyhow that took care of the lights on the dash. Back in service. Thanks again Bill .

[billofdurham]

Welllllll - never thought of that one.

Thank you for the update.

Bill.