1985 Cougar Voltage Drops when driving, Charging issue?

October 23, 2019, 11:07:45 AM

Hello Guys,

Having some issues with my stock 1985 Cougar LS V6 charging system. Looking for ideas on what my be the problem.

When Accelerating and or at a speed around 40MPH or more my voltage gauge drops to around 10(On the digital dash gauge its one bar above the Very Low cutoff). I also get static interference coming thru the stereo speakers when the voltage is low like that. As soon as I take my foot off the gas/come to a stop/ coast etc, the voltage jumps up several notches to the normal level.
I can see the dash lights dimming and brightening when in these stages as well. When I drove on the freeway at 65MPH for 10 miles the gauge stayed very low and the battery icon even started blinking at me. So it doesn't seem to be charging unless the car is idling or or the RPM's are low when driving at slower speeds.

A few weeks back before any of this was noticeable the battery died on me so I got a new one (after the store charged it they came back saying it had a bad cell).
Car ran for 2 days and died again. At that time I put on a new external voltage regulator and new alternator.
Since then its ran but I've noticed this voltage drop issue and the static interference thru the speakers. The stereo is aftermarket and has a older amp hooded up, none of which I installed, not sure how much if any that may have to do with it.

Any ideas?

Thanks
-Dennis

Re: 1985 Cougar Voltage Drops when driving, Charging issue?

Reply #1 – October 23, 2019, 11:24:43 AM

Is the charge wire tight and in good condition? Could the serpentine belt be slipping on the alt pulley at higher rpms? Check the charging grounds and make sure are tight and good.

Not sure, just trying to help. Seems odd.

It didn't do this with the old alt, did it? Maybe a bad new alt?

Re: 1985 Cougar Voltage Drops when driving, Charging issue?

Reply #2 – October 29, 2019, 04:56:57 PM

With your multimeter, check the voltage at the battery terminals.
Engine off=12v?
Engine running=14v ?
Engine revving=14 v ?
If no 14v:
Turn engine off and check for 12v at the black/orange wire on the Alternator. If no 12v you have a blown fuse link.
The black/orange wire goes on the alt terminal labeled B
The orange/light blue wire goes on the terminal labeled F
The white/black wire goes on the terminal labeled S