Blown Fuse Link and Now No Power at Ignition

[ZNate]

Have a 9/70 240Z with a blown fuse link and no power at red-white at ignition.  This happened last fall before car storage, so I have researched over the winter and have worked on the problem for many days.

Test 1:
Everything still connected, except fuse link.  Ran jumper from fuse link connection to solenoid while key turned to start.  Had spark when jumper wire touched solenoid.  Solenoid appeared to engage a little.  Same test/result we had last October.

Test 2:
Everything still connected, except fuse link.  Ran jumper from solenoid to positive battery terminal, but had no response.

Test 3:
Same as #2, but disconnected positive battery connection from battery.  Ran jumper from solenoid to positive battery terminal, but had no response.

Battery and starter(s) pass test at auto parts store.

1. New battery cables.
2. Cleaned all starter and battery connections.
3. Cleaned the two grounds (above the battery on the firewall and along the frame where the “white” (yellow on diagram) fuse link connection comes out of the harness).

I started testing the original ignition and found no red-white power coming into the key.  This suggests, battery, power connections, grounds or something along the red-white from the key to the battery.

Would appreciate your help.

Thank you!

Nate
 

 

 

 

[siteunseen]

Could one of the small glass fuses under the radio have blown when the starter link failed. I'm pretty sure there's one for ignition.

[ZNate]

Thank you for the reply.

All the fuses are good.  Just removed the in-op ARA evaporator to inspect the wiring.  No analysis yet.

[Zed Head]

With everything turned off, use a meter and test for a dead short from the fusible link terminal.  You never described why or how the fusible link blew.  Somehow you're on to hot wiring the solenoid.

[ZNate]

Appreciate the reply Zed Head.

Have no idea why or how the link blew, it just happened one day.  Car drove fine before that.  

Of all the car work I've done, I have never had to search for an electrical short.  Guess I'll need to search google for some how-to.

[Zed Head]

Electrical is difficult to learn but powerful once you get some basics down.  A test light is a simple starting point.  An inexpensive meter would be the next level.

[ZNate]

Minor Update:

Retested the battery, solenoid and starter today; successfully got the starter to spin the engine.

Removed and labeled all fuses in block; then installed one at a time and tested circuit by using a jumper between the fuse link spade and the 8mm solenoid bolt.  Repeated adding one fuse at time and testing circuit until all fuses/circuits past the test - no or very little spark when jumper touches solenoid.

Off for a few days, will update when I return.

[ZNate]

We found the short causing the fuse link to blow and my Z is running again.

While waiting for an auto electrics expert to help me, I discovered melted connectors on the defrost switch.  The switch was left on by mistake causing the short issue.

The switch was non-OEM, with a built-in light and a PO cut the console plate to install the switch.  The switch light was burned out, so it was easy to miss that it was on.

My expert arrived at this point and he set-up a 12v light bulb to help identify the short.  He also added a 25 amp push button fuse to protect the circuit during testing.  

The bulb lit when connected to the circuit, so he knew there was a short. (I do not know how he connected the test light, since I was in the driver’s seat).

He suggested that we remove the Accessory Relay, since it is part of the defrost switch circuit with a potential problem.  With the Acc Relay removed, the light went out, so the short was identified somewhere in the Acc Relay circuit.

I traced the three defrost switch wires: 1-Ground to cigarette lighter body screw, 2-to a female connector and 3-to a female connector with an inline fuse. 

The inline fuse contained a 25 amp fuse with a small burn hole. The inside of the holder was brown, plus part of the wire was melted and exposed. 

I cleaned the holder and copper connection inside, plus I put shrink wrap on the burned/melted wire and inserted the proper 20 amp glass fuse.

See attached photos for before/after repairs.

Before connecting everything back up I tested the accessory relay circuit.  With the relay still detached, I used jumper wires to connect three of four pins.  Between the blue-red wire, I attached a 12v bulb.  I turned the key slowly from lock to start.  The relay clicked correctly at ACC and the bulb did not light as I started the car.

Success!  No light = short fixed.  If the bulb burned bright, we would have still had a short.

With positive test. I removed the temporary push button fuse and installed the correct fuse link.
The Z starts and runs fine again.

Appreciate everyone’s assistance with getting my Z operational again.

(My Z now blows the brake light fuse when the turn signals or hazard lights are used.  Will do a separate write-up to discuss.)

Nate