Hello everyone,

I'm currently having a pretty serious problem with my `93 VDP, in that the output from the alternator varies significantly. Most of the time, it runs at about 15 amps, which from what I understand, is fairly high, but randomly drops down to around 13 or so, causing my headlights to dim, the AC blower to vary in speed, etc. Unfortunately, this doesn't just happen at idle, it happens while driving as well, and I suspect it to be some of the reason why the 20 Amp Sunroof fuse keeps blowing out occasionally when I start the car.

I have replaced the alternator entirely, so it's probably not the voltage regulator, and checked all of the connections that I could, but still can't find the problem. My thought is that it could be the battery cable running from the trunk through the car that could be corroded, since I did a voltage drop test that revealed I'm losing about an amp from the battery to the engine.

Any suggestions on how to address this problem? I think it's already blown out the audible warning speaker, so it could very well start damaging other, more expensive bits like the ECU module.

Really appreciate any thoughts you all might have!

EDIT: Also, forgot to mention that I do have an aftermarket stereo and a 500 Watt Amp+Sub in the trunk, but it seems to make no difference if I disconnect it.

 

You say the output is up to 15 amps at times. Do you mean volts? The alt should be supplying a steady actual 14.6 volts, with the amps varying as needed- up to its own limit of course. I definitely agree that blowing fuses is a problem. I think the first thing i would do if the volt output is actually too high would be to take the alt back to the seller (if possible, if not then elsewhere) and have it checked. It isnt beyond reality for new rebuilts to be defective out of the box. I hope its a simple fix in any case. Good luck.

 

Hi gpwicks,

I'm sorry to hear you're having electrical gremlins. Just to be sure we understand, were you having all the same symptoms before you replaced the alternator/voltage regulator?

Also, do you mean the alternator is producing 13-15 amps or 13-15 volts? Amps and volts are units that represent entirely different properties. Off the top of my head, your '93 should have an alternator rated for 120 amps, but which should produce something like +/-13.5 volts to +/-14.5 volts depending on engine rpm.

Are you measuring the alternator output with a separate meter, or viewing the voltage on the gauge in the instrument cluster of the car?


Again, just to be clear, do you mean that your voltage measurement in the engine compartment (either at the alternator or starter) was 1 volt lower than the measurement at the battery? Or do you mean something else? A very common issue is corrosion on the large jump-start terminal on the right firewall near the row of relays. This terminal connects the battery power cable from the right-side fuse box to the starter and alternator, so it pays to remove the large brass stud (I think it takes a 19mm socket) and thoroughly clean the ring terminals on the wires that connect to it.

My first instinct is that these are unrelated issues. Both wires to the audible warning speaker connect to the CPU, so it's unlikely that an over-voltage condition would damage the speaker voice coil without damaging the CPU as well. The speakers just fail with age. I found a suitable replacement at Radio Shack for a few dollars - just note the outside diameter, total height of the speaker, and the rated impedance, and any speaker that will fit in the space with an impedance equal to or higher than the stock speaker should work.

The sunroof fuse could be blowing due to a short in the sunroof motor or switch wiring or a water leak at the sunroof seal or plugged sunroof drains (pretty common). I'm not sure how the fuse would blow simply because the alternator was supplying too much voltage unless there was a path to ground through the fuse even when you were not activating the sunroof switch.


Are the failed speaker and blown fuse the only symptoms that have caused your concern that the alternator may be producing too much voltage, or do you have other reasons that have contributed to your concerns?

Cheers,

Don

 

Thank you all for your helpful responses. I do in fact mean volts, sorry about that, had it reversed in my head for some reason.

To clarify, I did mean that the voltage at the alternator was 1 volt lower than the voltage at the battery, tested using an external meter. These symptoms were happening both before and after I replaced the alternator. While it's possible they both have defective voltage regulators, it would be very odd.

The main reason I'm concerned is that whenever I drive the car, there is noticeable fluctuation of the dashboard lights, head lights, stereo volume, blower speed, and so forth. Granted, this could be exaggerated recently by cold weather and poor conditions, but it's still problematic.

I'll definitely look into cleaning the terminals on the right side fusebox connections, and see if that helps.

You're probably right about the sunroof having a short, since there's been a TON of snow (at least from my perspective) where I live on the east coast, and some could've melted onto the sunroof motor, causing the fuse to blow. I've checked all the drains with compressed air, but they all seemed to be clear. It's good to know that the speaker issue is unrelated, and I've got a replacement for it a while ago, so that'll be an easy enough fix.

Again, thanks for all your help!

 

Hi gpwicks,

You probably have more than one issue going on, and a good automotive electrical service shop may be able to find it faster than you can, but if you want to rule out some of the possibilities, you can clean all the battery power connections, all the grounds (especially the ones in the engine bay and the battery negative cable to body connection), service your fuseboxes and reflow any cold or starved solder joints, and do the same to all the relay modules behind the passenger-side knee bolster. Below are links to photos showing all this work except for the insides of the relay modules (the last album does identify the modules though):

Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page

You should also check for water or corrosion on the electrical connector for your CPU and possibly inside the CPU case. It's also behind the passenger-side knee bolster but you have to disconnect several items to access it.

Sorry for such a long list, but you've definitely got some odd symptoms. As I said, a good automotive electrical service shop may be able to track down the problem faster than you can.

Please keep us informed.

Don