I have an 89 Cabrio that will not show more than 13 volts, and dips below
12 volts with lights and blower on. I was told that the voltage regulator was adjustable, but I don't see how. The alternator checks out okay and the voltage regulator is new. Any ideas?
When you say the alternator checks out OK, what kind of tests have you done one it? If your battery is bad, it can present such a big load that the alternator is not able to get up to the nominal 14V. How old is the battery?
Is the 13V measured at idle? What happens if you rev the engine up to something like 2000 RPM?
Engine speed makes virtually no difference - reving up to 2000 or beyond has not effect. The battery is a year old, fully charged. I never see that nominal 14V. The alternator has had the standard bench tests and is putting out "good power"...
1- at alt
2- at battery
3-at the gauge in the console
If 1 & 2 are around 13.8-14.1v then there is no problem with the ALT and the regular isn't adjustable. The lower voltage inside is something that has always been an issue with the old cars. My opinion it has a lot to due with resistance in the electrical circuit some from age and some from original design.
Have you checked your grounding straps, this one had me scratching my head for a few months. Take some booster cables and short the negative batery post to the case of the alternator. If you see any sparking or if the engine load/rpm changes it'll be your grounding.
I'd run 4 or 8 Ga. wire (250 strand) from the alternator directly to the +ve terminal and clean every contact you can find as everyone else has indicated.
From a Google search of a post I did a long time ago:
Augment the Ground wires and recondition the electrical connections;
Replacing the Battery's leads (Ground to Frame/Block & Pos. to Starter)is an easy & cheap restorative.
Replacement cables are plentiful at local auto parts places.
Cleaning and a _light_ coating of the cables' contacts with (at least) some Vaseline will prevent future corrosion from returning.
Adding an _additional_ wire from the Alternator's CASE to the engine block (reread that to be sure you dealing with the Alt's outsides) will help w/ the 'flow of electrons'.
"I'd run 4 or 8 Ga. wire (250 strand) from the alternator directly to the +ve terminal and clean every contact you can find as everyone else has indicated."
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