Electrical issue.

[hilaegis]

Hi. I haven't posted much because my truck has been on the back burner. I did get great help about my gas tanks. So, I have a 1987 that was a diesel and the PO swapped in a 305 with carburetor.  I went to start the other day and nothing. No power to anything except the clock.
What I have done:
Tried to jump start nothing
Battery reads 12.5 volts
Checked for power at starter Yes
Checked for power at alternator Yes
Checked for power at junction on firewall Yes. Back probed at bulkhead and both red power wires have 12.3 volts. I took bulkhead apart cleaned and greased.  Now I have 12 volts at light switch but still no lights. Checked fuse for ignition and with a power probe it shows ground and multimeter less than a volt.
I checked grounds from battery and engine to firewall and they have ground. I cleaned them up too. So I am at a loss. I think it points to bulkhead connector or fuse panel. Could really use help. Thanks


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[bd]

The battery cable(s) may be corroded internally where it's hidden from view.  Measure the voltage drop across each battery cable, end-to-end, while trying to crank and post your results. 

[rich weyand]

If the battery cables are more than ten years old, just replace them.  We have had several cases recently of battery cables corroding internally with no external sign of problems.

Testing voltage on the starter or fuse block while cranking will tell you if it is the cables.  They can read full voltage when not carrying current, then have a big voltage drop when trying to crank due to the current through the (excessive) cable resistance.

The clock working doesn't say much.  Most auto clocks are spring clocks, that use a solenoid to rewind when the spring runs down.  They don't use any current when running on the spring.

[hilaegis]

Thanks for the replies. Can I tested cranking without power to ignition? 
I will get new battery cables tonight.


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[rich weyand]

Can I test cranking without power to ignition? 

Yes.

[hilaegis]

Can I test cranking without power to ignition? 

Yes.

Ok. I will give it a try.  Thanks


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[bake74]

     One more thought, my son's blazer had a problem like this, it ended up being the fuseable links that are located off the starter (shares the main battery input to starter, see diagram here, top of page below and right of starter  (  http://www.73-87chevytrucks.com/techinfo/wiring_diagrams/81-87_V8_engine.jpg ) ).

    The blazer would not start one day, did my run down with the meter and everything checked voltage wise, but as soon as a load went to the fuseable links they stopped the flow of volts.  Replaced and started right up, this could be your problem.  The easiest way to check this is have someone turn the key on and you check the voltage downstream.

[hilaegis]

Thanks. I will try that tomorrow.


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[hilaegis]

It snowed and I do not have a garage so it was fun, but I changed the battery cables. Voltage drop was .1 volts to starter.  Cranking made no difference.  However, now I do not have any voltage at the junction block on the firewall. So I am guessing the fusible link by the starter?  Thanks again for the help.

[bd]

There should be two fusible links coming from the battery cable stud on the starter solenoid.  There is a third at the firewall junction block.  Give them a gentle tug and see if they stretch like a rubber band; inspect their insulation and terminal junctions for signs of heat damage.  For detailed technique on replacing fusible links, see How to make a Fusible Link.

[hilaegis]

Thanks. I will take a look at them


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[hilaegis]

Thank you to BD, Rich Weyand and Bake74!  I replaced the battery cables as I stated and checked the fusible link by the starter.  It looks like the PO just twisted the fusible link and red wire together.  When I took off the electric tape the connection just fell apart.  So I fixed that connection and it started right up. 

Thank you.  I appreciate your knowledge and experience.