Samuel,
I got your email with the photos. That's a REALLY old isolator. I don't
think I'd ever seen a real, OEM, GM labelled one before! Too bad you're
probably going to have to replace it. But before you do, you should test
it, both to ensure that it's really bad (or good) and to let you learn a
little about them. Before we get into details of that, let's agree to quit
using those meaningless terms "top, bottom, etc." and call the terminals
what they are: The middle terminal is for the Alternator. The other two,
when disconnected, are identical in function, so when connected, they
become either House or Chassis terminals, indicating which battery they
serve.
To test the Isolator, since I know you have a multimeter, use it. With the
lowest Ohms range selected, touch the two leads firmly together and be sure
the display reads at least close to zero. When they're not touching, it
should read as high as it's capable of -- "infinity". Now, with all leads
disconnected from the Isolator:
1. Put the Positive (should be Red) lead on the middle terminal and the
Negative (should be Black) lead on one of the other terminals.
2. Note the meter reading. It should be nearly zero or nearly infinite.
Remember that.
3. Now move the Negative lead to the other terminal, keeping the Positive
one in place. Read the meter again and remember what it says. It SHOULD
read the same as before; if not, the Isolator IS bad. We'll find out which
side in the next step.
4. Swap the locations of the leads (Negative to the middle terminal) and
do the same two tests you did above. Anywhere you read zero before SHOULD
now read infinite and vice versa.
5. If either test does not reverse its reading, the diode between those
two terminals is bad. If the unchanged reading was zero, the diode's
shorted; if infinite, the diode's open.
6. If there's not a defective diode, the Isolator should continue to work
fine. Otherwise, buy a new isolator.
But while waiting for a replacement Isolator, you can continue with all
other tests -- remember that the ONLY thing the Isolator does for you is
prevent the batteries from being drained together when the engine's not
running. And it's not even needed with the Sense lead connected to the
Alternator Output.
Johnny's already given you some hints about checking for shorts. IIRC, you
already tested the circuit from the House battery to the Boost solenoid and
repaired the deteriorated insulation on that cable. If not, complete those
tasks now. Since you've repeatedly reported seeing the same voltage at the
Chassis battery and at its connection to the Isolator, I'm confident that
circuit is in good condition. However, the reported voltage is that of a
DEAD battery, which makes me ask, "How did you start the engine?" The
answer to that may be significant.
Ken H.
On Sun, Sep 22, 2019 at 11:48 AM Samuel Ferguson via Gmclist <
> Johnny,
>
> I did fond the booster cable to have coating missing from it along the
> framing behind the grill area. I have unhooked the booster cable from the
> solenoid on the firewall engine compartment. I checked the cable to the
> connections block located behind the converter and found the cable to appear
> to be in working order (no other shorts/grounding) other than what I found
> it to be touching the frame behind the grill. I have insulations material
> ordered to recover the exposed sections (which is approx. 3 feet). But for
> now the cable is unhooked and no power running to it. My house batter y is
> new and it is still holding a charge.
>
> Samuel
> --
> Samuel Ferguson
> Pittsfield, Illinois
> (West Central Illinois)
> 1976 GMC Palm Beach (A newbie who will not allow this thing to kick my
> butt!!)
>
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Now,
