Driving home the other night I noticed the gauge on my 87 showed only11.1 volts. I got home and put the meter on the battery with the car running and only got a little over 11 volts.. The next day I took the alternator off and took it the my auto parts dealer who checked it and said it was fine. He suggested I replace the external voltage regulator. Since it was only 20.00 I bought one but can't find where it goes. The parts guy said it was on the drivers side near the headlight. It looks like it fits inside another housing but I can't find anything that looks about the same size. As a side note, after I reinstalled my alternator, it has been reading over 13.1 volts until today and once again it's showing low voltage. My Haynes manuel does not show any drawing or instructions concerning this, any suggestions?

 

You can get parts for that cheap CS-130 alternator but the best out is go buy who evers parts store you likes LIFETIME WARRANTY Alternator and be done with it. Hou do I know? My 87 has had 5 alternators on it since I've known the car. I bought 1
Long ago a auto electric guy told me 4 yrs was good for an 80's GM alternator. There is no engine driven fan and they overhead and burn up.
A lower temp boost fan switch and a reprogramed main fan will help and a good charged up battery. I'm sure low battery killed at least one on my car.
All the parts inside that alternator are soldered in place. They are nothing like a good on GM SI alternator.

JS

 

First, the Haynes manual is garbage. You will not find an accurate wiring diagram for the car in these types of manuals. Get the 1987 Factory Service Manual set. The second of the two-book set has all of the electrical wiring diagrams for each system and component locators.

Second, there is no external voltage regulator; the regulator is part of the alternator. Don't know what the guy sold you but he's wrong . The only thing on the driver's side of the car by the headlamps are the three relays that control the headlight motors and a relay for the auxiliary cooling fan if your car is equipped with one.

It sounds like the voltage regulator is failing intermittently. What you need to do is to use a digital voltmeter to check alternator output at the large terminal where the large red wire attaches. Do that when the dash displays the low voltage. Also check the battery voltage across the two terminals.

A fully charged battery in good condition should show around 12.8v with the engine off. The 13.1v you see is still somewhat low; even after driving around, the display should read around 13.6 to 14.0 volts with the engine at around 1200 RPM if the alternator and battery are in good condition.

How did he check tha alternator? Did he put it on a motor that spins it and then checked for voltage at the output terminal??

 

Thanks, for your input. Ihave changed alternators before but was having a hard time believing there was an external voltage regulator. You are also right about the Haynes manual. It's hard to follow and poorly written but it happened to be the only one I had. Thanks for your help.

 

To answer the last part of your memo, yes he tested the alternator by putting it on a test bed and spinning it. Two tects looked at it and said it tested OK.

 

C4cruiser is right.

You want to measure output voltage between ground and the thick red output wire on back of the alt with engine running. It's got a black rubber cap on it, underneath it's held down by a nut.

Then repeat at the battery. You should get an identical reading across the battery terminals.

Note that the guage voltmeter is off by about .3 volts too low compared to actual voltage at the alt and battery. Your readings are still low though.

You also need to have battery voltage at the two smaller wires on the alternator harness connector.

One red and one brown. Terminals L and S. Unplug, turn the key to the "on" position but motor off, and check for voltage to ground with a voltmeter on each one. These power the internal regulator inside the alternator.

There is no external regulator.

 

Sounds like you may have a poor engine ground or the connector pins on the alternator connector are pitted or corroded.
Again, the monkeys behind the counter are usually book experienced, and can only regurgitate what they see in a book.
They may have confused an early 63-72 corvette alternator with yours.

 

87 alternators have the voltage regulator mounted INSIDE the alternator, not outside. At 11.1 volts, you have a totally discharged battery and you should charge it up. Normal alternator output voltage is 14.3v (dash voltmeter) cold and it drops as the alternator warms up and is 13.3v at its operating temp. The voltage reg could cause no alt output, but there are also other things that can cause no alternator output, a blown fusible link, open diodes, broken output wire on the inside of the alternator going to the output bolt. If the store test of your alternator shows it is good, then disconnect the neg battery cable and measure the resistance between the positive battery terminal and the output terminal on the alternator to test for a blown fusible link. It should measure the same as touching the ohmeter probes together, or very very low resistance too low for conventional ohmeters to measure. You can replace the fusible link.