Bill Ball

A buddy called saying his 88 S4 had no electrical power. I told him most likely the battery had gone flat, but that proved not be the case. When I went over to check out the situation I found 12.5 volts at the battery. None of the interior lights worked. When I switched on the headlight switch, the dash lit very dimly. When I inserted the ignition key and twisted it to start the car, everything including the instrument lights was completely dead. I decided to clean the battery ground point and noticed no spark at all when the ground strap was pulled or reattached - essentially no current flow.

A few minutes later I turned on the headlight switch and the interior lights and instruments lighted up brightly and I twisted the key and the car started and ran normally. I shut it down and then everything went dead again with no response to the key.

The ignition switch is about one month old, installed after the owner reported erratic starting that he could overcome by wiggling the key in the switch. I understand there have been some bad ignition switches released recently and this may be one of them.

The only puzzling thing was that the voltage at the jump post in the engine compartment only registered 3 volts. Could a bad ignition switch account for that or do I need to look further?

Speedtoys

Whats the condition of the entire ground strap?

Just replaced mine..I had about 1" of ugly on it.

danglerb

Battery, big fat wire, starter, big fat wire, alternator? or jump post?

Is the 14 pin in there?

Sounds to me like a bad ground and you have current flowing through the backwards connection to another ground point.

Alan

No - it isn't the ignition switch - it isn't even in that circuit.

It could be a ground strap - quite possible.

Alan

Mrmerlin

add a battery cable jumper wire to the neg post and one of the shock tower nuts see if you have power,
where was the ignition switch purchased from?

I would be betting on a bad ground

depami

What Alan and Stan said.


Where was your negative meter lead when you measured 3 volts at the jump post?

Put a really long wire on your negative meter lead and measure from jump post to battery negative terminal.

If still no good then it's in positive cable. Check connections at alt./starter.

If good when reference from battery negative terminal, then it's likely the ground strap.

SeanR

Check the connections at the starter. Had one do this and the feed lines at the starter were not tight.

Randy V

No.

RET

Easy check of the ground strap: place one lead of a volt meter on the negative teminal post of the battery and the other on a good chassis ground, and turn on the headlights. If there is more than a nominal voltage drop (millivolt range) across the strap as shown on the meter when the load is applied, then you likely have a bad strap.

Bill Ball

OK, it looks like everyone is unanimous. I figured the ignition switch could not do this. The strap and ground point LOOKED OK, but I've seen ground strap pictures here that showed heavy corrosion under the insulation. Thanks for the suggestions on testing further to determine if it is the ground or possible the positive cable or junction at the starter. Since ALL power everywhere is dead or close to it, I'm suspecting the battery ground. However, I think I put the meter across that ground and saw 12.5 volts. Will test further.

THANKS!

Alan

12.5 volts across the ground strap means its bad.

BTW this is a dynamic test not a static test (weird as that seems). With battery in circuit - put the voltmeter across the strap (negative post - ground point) and flex the strap as much as you can. It is highly likely you will see huge variations as you do this on a marginal strap - all the way from ~0V to full battery voltage...

Since every time you install and remove a battery you flex the strap - this is why debug becomes difficult - since replacing a battery or charging it can seem to fix everything (for a little while...)

So you may have to stress it repeatedly to see it. In any case cut off the sheathing and evaluate it.

Alan

AirtekHVAC

My positive wire at the starter was all corroded and green....could be there...

SanDiego928

Replacing the neg strap has seemed to fix my ignition issue. Overall the car seems to start and run better.

LT Texan

I always used this test, with the headlights on, crank the engine.

If the headlights lights dim significantly while trying to crank - battery is dead.

If they don't, crap ground or battery connection.

Alan

Ahh... No. That is not a good test.

A bad ground strap or bad battery connection can look exactly like a bad battery (or not).

It can also be bad (as described) and most of the time can work quite perfectly - so no test like this is in any way conclusive.

You must directly test and flex the strap while testing to evaluate for this failure mechanism. It is quite counter intuitive - I know - but yes a big thick strap can actually be a conductor one moment and an insulator the next...

Alan