Tampa 928s

Took at test drive tonight and lights were very dim and got worse. The measured battery voltage with car running 13.72 Volts battery shows 12.20 volts off. This has gone on for a while I keep charging it battery is almost new. Since I keep working on the car this is the first night drive any feedback.

Mrmerlin

might have a lose cable on the either the battery or the alternator, the charge seems about right its over 13.5,if its less than that it usually indicates a blown diode in the alternator. Also check the hot post connections, remove the 14 pin connector and also hot post 11mm securing bolt with the battery disconnected of course

85fortheDrive

First thought is that this is a failing alternator.
When you turn the key to just before the ignition point, does the low voltage light turn on?
What does the voltage read when the engine is running?

Tampa 928s

Gauge with full charge battery it reads around 13v doing this by memory, then it goes down to 12v. No the light never came on. Odd the headlamps are so low could not even see although the battery read 13.7 with car running. I'm going to check out all the starter, alternator connections tomorrow. I should see 12v with key on on the small red exciter wire on the alternator, correct?

SharkSkin

Sounds like the charging system is OK if you're @ 13.7V running -- doubly so if that's with lights on. Check/clean the connections at the jump post, the drip cover gets lost and that corrodes quick. Also the 14-pin connector next to it. If all is well there, check the large cables that attach with ring terminals and nuts on the studs that stick out from the top of the central electric panel. Also, it could be a slipping pulley on the alternator that gives enough juice normally but slips under load as you begin to turn on more electrical devices.

Tampa 928s

Sounds like the charging system is OK if you're @ 13.7V running -- doubly so if that's with lights on. Check/clean the connections at the jump post, the drip cover gets lost and that corrodes quick. Also the 14-pin connector next to it. If all is well there, check the large cables that attach with ring terminals and nuts on the studs that stick out from the top of the central electric panel. Also, it could be a slipping pulley on the alternator that gives enough juice normally but slips under load as you begin to turn on more electrical devices.
__________________

Jump post is fine I cleaned it recently now its under the S/C pipe so another job to do. Why would the 14 pin connector cause the head lamps to be dim I mean hardly on at all.
Belt is new with S/c and it was doing this before the install.

Mrmerlin

just seperate the 14 pin and clean the pins with a pink eraser,the pins corrode fast since a lot of cars dont have the hot post cover fitted, then when the car gets wet from a wash or rain the connector gets wet and there is elex going throught it .
Also have the headlights grounds been checked? near the front of the engine compartment?

Tampa 928s

No the headlight grounds have not been checked but the low battery condition on the gauge has been going on without the lights on. With everything done on this car I am going with a connection problem. It seems like its an current issue not a voltage issue.

Bill Ball

The voltage read on the gauge can go down to 12V or lower at idle, especially if the headlights are on, but should pop up to 13-14 once you anywhere above idle. Do the headlights get brighter when you rev the motor?

Tampa 928s

No low beams checked fuses, charged battery last night. I worked under the pass fender installing the S/C filter and cannot find any disturbed wires. Just cleaned the Main ground and checked the fuse panel grounds all OK. Any common point to the headlamps? Gauge still shows low battery fully charged, starter wires look ok.

Mrmerlin

check the grounds in the front of the chassis near the edges of the headlight tube as they pass into the fenders

Alan

What exactly is the problem here...?

From everything you have said the alternator is fine and working as normal - don't chase any ghosts....

If you are worried about the battery voltage - first steps:

Remove the battery & charge overnight

Test the voltage without installing it - if it reads 12.6v or above the battery is OK. If it still reads 12.2v you need to replace it.

If it seems good - install it - test the voltage - did it go down?

If its still >12.6v turn ignition to accessory & then off - whats the voltage now, then try turning to ignition (not start) & then off how about now ?

I think its likely you have some current flow even when the car is off - and that can discharge the battery and also cause the voltage to be lower because the battery is supplying some current. If this is the case you need to debug he parasitic current draw - how much and where is it going...

The headlights dimming while driving is probably a totally different issue - connections, grounds - something. If your system voltage is 13.7v and you don't see fluctuations the headlights should be bright.

Alan

Tampa 928s

Allen

I agree with my gauge showing low and the dim head lamps I assumed it was the Voltage. Charged the battery last night went to 13.45 Volts opened the doors battery went to 12.43 which is fine. I get the same voltage on my exciter wire as the main alternator post or close to it with key on. With key off exciter goes to 0 volts which is correct. Seems there maybe a connection issue in the pod or the gauge.
As far as the lights that got me off track, I removed the pass fender well to hook up the air cleaner but don't remember any grounds in that area. I cleaned the block main ground, Coil energizer grounds near front radiator. I see a group of grounds near the Receiver Dryer that looks fine and dirty but it will take a lot to remove and clean those. Any other place to look for the lamp circuits, fuses are good it was dim last night now low beam is dead.

Dennis Wilson

With that much voltage drop either the battery is bad (needs load testing to determine) or you have high resistance somewhere in the primary voltage path. On an 86 928 the positive battery cable has probably seen better days and may have corrosion under the covering near the battery which could cause this problem. Also, the positive cable connection at the starter could be loose/corroded. BTW there are alternatives to buying the factory battery cables. If you need to replace yours, a check of the archive should be in order.

Dennis

Alan

Again - stop - think...

I guarantee you do not have 13.45 V on your battery unless A: the car is running or B: the charger is still connected...

If your measurement device is telling you this it is lying - get another one...

When you talk about battery voltage - it must be a test when the car is not running...

When the car is running you are measuring the system voltage which is the alternator output - to a first order the battery doesn't matter in this case...

I'd still suspect parasitic leakage is an issue with the battery discharging - do the appropriate tests - many posts on this already.

The headlights dimming - simplest check - remove the pod covers (3 screws) evaluate the bulb connections - test the voltage levels with the car running & headlights on.

With the low beams on measure the voltage between a ground point and:

The jump post in the engine compartment
The low beam supply to the bulb
The ground to the bulb

What voltages do you get?

Also are the high beams similarly affected or different?
How about the fog lamps?

Dennis - if there was enough resistance in the primary battery circuit to dim the lights appreciably the car would never be able to start... as Dave said earlier its possible there is a connection issue between the alternator & the jump post & Central Electric panel. It might be worth cleaning those connections:

Alternator main terminal, starter main terminal, jump post & CE panel top (2 terminals). But - if the jump post voltage measurements with headlights on still seem good this is pretty much a moot point.

Alan