jmartins

Today my son and I was working on my 928.

I removed the starter to change the buches and left the wire harness umprotected on the ground . My son, using one stick to pick some tool on the ground, accidently short-circuited the starter wires and now I have no power on the car.

No lights, fuel pump, coil, nada...

Could my ignition switch is dead? Is there some master relay or fuse anyware out of main relay panel?

Thank you guys!

jmartins

Mine is a 78 EURO.

Thanks

76FJ55

There is no fuse on the line from the battery to the starter. You need to start running a few test to give us more to go on.

What is battery voltage?
What is the voltage at the jump post?

dr bob

Disconnect the battery cables and carefully remove the battery. There's a reasonable chance that the battery has damaged itself, so use care and wear a plastci apron and rubber gloves if there's any evidence of damage to the case or acid leaking in the battery well. Clean and neutralize the area as necessary.

With the battery out of the car, use a Volt meter to see if there's any power available at the battery terminals. A charged battery should show about 12.6 Volts at rest. If it's less, use a good battery charger to restore the charge level.

Almost any repairs or maintenance to the car that includes working on the wiring deseves a moment to disconnect the battery ground strap.

The battery itself is a high-current source of electricity, and needs to be to crank the starter motor. Meanwhile, a 'dead short' as you might experience by grounding the positive cable to the chassis or engine, can cause almost instant heating of the battery itself. There's the risk or warping the plates internal to the battery, and if they do warp and touch, the battery is instantly junk. If the heating continues unchecked, the vaporization of the electrolyte can quickly get to explosive force. The case will swell at minimum, and there's a serios risk of a case rupture. That can be a disaster if you happen to be standing near it, and at best very inconvenient with all that acid leaking from a fractured case.


Anyway, your early steps include finding out whether there's voltage available from the battery.

jmartins

Thank you guys for the reply!

Battery has 12.3V did check for internal short-circuit with a smart battery charger, and it passes OK.

No voltage on hot spot at engine compartment.

No signs of burn or burn smell on engine compartment, starter wiring and main fuse box.

Any guess?

Thanks a lot!

j.kenzie@sbcglobal.net

A marginal ground strap, that melted when short occurred?

jmartins

It´s very frustrating... after months fighting with the fuel injection... when I finally found the problem - a big one for instance, return fuel line clogged - now this electrical mystery.

3 years working on this car, and for every step forward, 2 steps behind...

76FJ55

My guess is on ground strap as well. With the battery connected, and the system under load (turn marker lights on) check the voltage between the negative battery post and the chassis. use a point other than the ground strap chassis mount. if you see voltage then the ground strap is bad. let us know what you find.

Mrmerlin

take a battery jumper cable and connect it to the negative terminal,
then connect it to one of the shock tower nuts.

NOTE leave the ground wire connected,
if you now have power your original ground strap needs to be replaced

Wisconsin Joe

With all due respect, Dr Bob, I suggest disconnecting the battery any time you are working on the car anywhere near a wire that carries constant power.

You don't have to be doing electrical work to accidentally ground out a hot positive. Trust me on this one. I learned the hard way a long, long time ago. Unfortunately, I need to relearn it every now and then. I've blown fuses working on a variety of things on a variety of vehicles.

The "wingnut" on the ground strap makes it so easy that there's almost no excuse not to ("I don't want to reset my clock & radio presets" is about the only one).

jmartins

Thank you guys for the ideas!

xI use to be very careful, and use to disconnect the battery very often... this time I forgot to isolate the wires... this is making me very sad! I'm a electronic engineer and no excuses to this fault.

I'll try to use a battery jumper to some another ground point, and the hot spot at engine bay as 12V source. Just to troubleshoot the problem, not to start the car.

Thanks again, and open to new ideas!

dr bob

Warniing well stated. My only 'exception' is when I'm troubleshooting electrical problems and my toolset includes the DMM.

dr bob

JMartins--

One thing that isn't mentioned yet is the current flow path between the battery and the rest of the car. The first stop for the primary wiring is the starter solenoid terminal, which is the connection you were working on when you removed the starter motor. Revisit that connection now, making sure that the red connections going forward in the car to the alternator are still intact, and on the same bolt on the starter solenoid as the feeder from the battery. Current flows from the battery to the starter, the starter to the alternator, from the alternator to the jump-start post under the hood, and from the jump-start post to the central electrics panel. You can test for voltage at each of those connections, referencing chassis ground, starting at the battery. You've already identified that there's no power at the jump post. Testing at each point from the battery to the jump post will isolate the break in the circuit to one of three possible sections of cable.

jmartins

Good point dr bob!

I'll do that!

Thanks

gsmarrara

Dear JMartins,
glad to see you in the rennlist. I have a 1983 928S auto, and I live in Brasilia-DF. Happy to see another 928 owners here. By the way, I also have a 1978 Maverick GT. Lets keep in touch, we may help each other to keep our cars running here in Brazil. My email is gsmarrara@bol.com.br. Hope you fix your car electrical problem soon.
Best regards, Gmarrara.