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George H.
George H., Technician
Category: Classic Car
Satisfied Customers: 18445
Experience:  Old enough to have worked on them when they were new
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1972 corvette. Replaced starter solenoid and wired back same

Customer Question

1972 corvette. Replaced starter solenoid and wired back same as I took off..turn key and starter does not work. I can use a screw driver to jump solenoid terminals and starter works. Took ignition wire off s terminal and tested 12.5v with key in start position.put wire back on s terminal and only gets 7.5v with key in start position. trying to get my starter to work ...any suggestions?
Submitted: 1 year ago.
Category: Classic Car
Expert:  George H. replied 1 year ago.

Hello I will help you with your question,

If you jump 12 volts from the battery cable at the solenoid and it will pull in and connect the battery cable to the motor cable but you only have 7.5 volts at the purple wire when you turn the key you have a voltage drop between the 12 volts applied to the switch and the start S terminal where the purple wire is connected.

Is there any evidence that other circuits fed from the switch are short on voltage?

Can you measure at the purple wire at the switch with the key in the start position to see if you have 12 volts there?

Customer: replied 1 year ago.

What are you calling the switch? The key switch?....yes as to other voltage drops..at the coil pos+ only when key is in start position

Expert:  George H. replied 1 year ago.

The ignition switch is where the purple wire that leads to the starter solenoid is fed 12 volts in the start position.

Is this an automatic or does it have a clutch?

Customer: replied 1 year ago.

Its a manual..I'll go check voltage from the ignition switch if I can find it...what's weird is with that wire off the s terminal gets 12+ volts but on s terminal it gets 7.5 is it because its has to be under load to get a voltage drop?

Expert:  George H. replied 1 year ago.

OK, on the manual the 12 volts runs from the switch through the clutch switch connector to the solenoid. If you find 12 volts at the switch (neutral on the trans please!) then unplug the clutch switch and use a paperclip to connect one side to the other and see if the solenoid is now getting 12 volts. Last place is the bulkhead connector, you may end up running a new wire but if someone put an aftermarket alarm in then they usually cut the purple wire and run it through a relay which they tie up under the dash.

Let me know what you find and if you see any aftermarket wiring up by the steering column

Thank you

Customer: replied 1 year ago.

Some after market wires...don't know if I can get to key switch without tearing column apart...wondering why wiring worked fine till I broke + off solenoid and replaced solenoid and now not working....main question I have before I tear column apart is why do I get the 12 v on the purple wire going to s terminal on solenoid while it is off the terminal? Then when I hook it up I get the voltage drop?

Expert:  George H. replied 1 year ago.

You can test at the clutch switch if that is easier to get to. If you see a square black box and another rectangular box about the size of a deck of cards, cut the ties that hold them up and check what the square box is connected to . Probably the purple wire.

Do you have a key fob or a switch to start the car?

Customer: replied 1 year ago.

Ok I will look for that... But I'm still looking for an answer as to why I AM getting 12v needed down to the solenoid with wire off s terminal?

Expert:  George H. replied 1 year ago.

A voltage drop only comes up when current is flowing in the circuit. The solenoid has very low resistance in the winding the purple wire runs so lots of current flows and if there is another point in the circuit that has a higher resistance then the voltage will "drop" at the high resistance point not leaving enough to run the solenoid winding.

Your meter has millions of ohms of resistance when you measure voltage if you disconnect the solenoid and measure at the end of the wire then you substituted the low resistance of the winding for the high resistance of the meter and with little current flowing you see all the voltage with the meter. Google voltage drop and there are many tutorials on how this works. You have a drop caused by high resistance in a connection or switch (relay) so keep the solenoid connected and check along the circuit to see where the voltage drops. If you need to slip a straight pin along a wire to allow you to measure inside a connection so you can leave it connected you can do that but you want a complete circuit when measuring.

With the fiberglass body on your car there is little ground available so checking voltage drop is a skill you need to work with this car.

Let me know what you find and how I can help

Thank you

Customer: replied 1 year ago.

Understand voltage drop now....found connector with purple wire to the clutch switch... It was unplugged and looks like that since I owned the car, but still started the car fine.guess I need to follow the purple wire back to the key switch till I find where it drops then that's my problem?

Expert:  George H. replied 1 year ago.

Great, check to see if you have 12 volts there, use a paperclip then measure at the solenoid. If you see the purple wire spliced into a relay or some other "black box" remove said box and splice the purple wire back together.

Let me know what you find

Thank you

Customer: replied 1 year ago.

Found many splices in the power wire going to the ignition switch..that is where the voltage drop was...thanks for your help

P.s. I burnt out the new starter solenoid testing the voltage with the key in start position...guess it got to hot..lesson learned.

Expert:  George H. replied 1 year ago.

Glad you found it, the solenoid should not have burnt so if it was not AC Delco you should use that brand. AC has moved many of its suppliers offshore so if it was one of those then that could be the reason, check the box for the origin.

Glad you found the problem, please let me know if you have further questions and you are now ready to find voltage drop issues as they come up.

Thank you

Expert:  George H. replied 1 year ago.

Glad you found it, the solenoid should not have burnt so if it was not AC Delco you should use that brand. AC has moved many of its suppliers offshore so if it was one of those then that could be the reason, check the box for the origin.

Glad you found the problem, please let me know if you have further questions and you are now ready to find voltage drop issues as they come up.

Thank you

Expert:  George H. replied 1 year ago.

Glad you found it, the solenoid should not have burnt so if it was not AC Delco you should use that brand. AC has moved many of its suppliers offshore so if it was one of those then that could be the reason, check the box for the origin.

Glad you found the problem, please let me know if you have further questions and you are now ready to find voltage drop issues as they come up.

Thank you