- Starter Relay wiring
- Red – 12V constant
- Black – ground
- Purple – starter feed
- Yellow – control signal (ignition switch)
We had a ’95 Chevy S10 towed in to the shop for a no start the other day, and I started with the usual; checked the battery cables for tightness and corrosion, booster pack to check for a dead battery, tap on the starter to check for a burned spot in the armature. No dice! We pushed the little guy in for further diagnosis. Once on the rack, I used my volt meter to check for power on the large (12V constant) post and the small (control) terminal of the starter which activates the solenoid and spins the starter motor. Finding battery voltage on the large lug, but no power on the small terminal during cranking told me that there was a problem in the control circuit somewhere.
The starter could still be bad, but I had to diagnose and repair the power circuit before I could determine that.
You can use back probing pins or unplug the relay for most of this testing, but I prefer back probing because the circuit is in tact and you can check for proper relay operation.
– I tracked down the starter relay and checked for power on the red wire (12V constant). No voltage here. I made a mental note and moved on to the other wires.
– Next, I used my Power Probe to check for a good ground on the black wire. You can also accomplish this by hooking a simple test light or volt meter to the POSITIVE side of the battery and back probing the ground wire. If the light lights up (test light) or you get battery voltage (meter) then you have a good ground. Check!
– Next step was to check the signal (yellow) wire for 12V during cranking. Check!
– Lastly, I checked the starter feed (purple) wire for 12V during cranking. No voltage here because there was no power on the red (12V constant) wire.
These tests told me that the ignition switch was good and the security system wasn’t interfering. The problem had to be on the red (12V constant) wire.
A visual inspection (and a faint burning electrical smell) led me to trace the red wire and the purple wire. I found that the fusible link on the red wire was burned through. So, replace the fusible link and it’s fixed right? Maybe, but what CAUSED the fusible link to burn through. The fusible link is like a fuse in that it burns in two if there’s a direct short, so I was looking for a short somewhere.
A visual inspection on the purple wire showed that it had been rubbing on the exhaust manifold (sorry, no pic) and shorted to it. A little electrical tape to replace the chaffed insulation and a zip tie to keep the wire safely away from the manifold and the short was fixed! After replacing the fusible link, the customer was back on the road for much less than a starter replacement!
If you come across a vehicle that doesn’t start, don’t just immediately replace the battery and/or starter before doing a little thinking and logical testing. If this post helped you, let me know in the comments section.
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