12V Starting Issue, help requested!

Hi Guys.

I need some help. I've got a 1986 Toyota Corolla (see readers' rides!) and it's been plagued by starting issues most of its life.

I've redone the wiring to the starter several times, and it typically works for a while after that, but inevitably it stops starting.

A little background: It was a SR-5 and I converted put in a fuel injected motor so I had to add the fuel injection relay and circuit main relay. Also, the battery is in the back.

So here's what's going on. I'm pretty sure the issue is the starter trigger somewhere. I've got a basic Fluke DMM I'm taking measurements with. When the battery reads 12V. and I go to start it, the starter trigger wire (unplugged) reads 11V (DMM grounded to chassis). When the wire is plugged into the starter, it only gets 5V (same chassis ground). When I connect the starter trigger to the battery directly it starts right up. I've got ground wires from the starter bolt to the chassis, and a couple other ground cables around the car.

I've had this issue with 3+ starters and I just replaced the contacts in this one.

Why would plugging the starter trigger into the starter cause it to drop from 11V to 5V?

Any input is really appreciated, I'd really really love to squash this gremlin!

I'll assume "trigger" means "solenoid" - the low current terminal on the starter that you apply power to when you want to start the car.

Terminology is crucial, donchaknow

You've already done a voltage drop test. Good. With that you have already diagnosed what is wrong! You should never see a difference from battery voltage on the side of the circuit before the load, in this case that load is the starter solenoid. You should see battery voltage there when cranking, let alone when the lead is off! A ONE VOLT DROP with no load on the system at all is a gigantic clue that there is some serious resistance in the circuit. Dropping to 5v when connected means that over half of the voltage is lost to a resistance somewhere in the circuit when under load. Find the point where you are losing seven volts.

So now, map out the entire circuit back to the battery and check for voltage drops everywhere convenient. Easiest is probably to check the voltage drop before and after the ignition switch, since that would be the most accessible spot.

Probably have a good spot of green death in a connector somewhere, or a crimp connection with only one or two strands actually in the crimp.

You're almost there, you have the tools to figure it out, now it's just a matter of finding the bad wiring/connection/contact.

Starter is fine. As said above, the reason it drops to 5 volts is because there is a loose/melted/green connection somewhere. Don't discount the contacts inside the ignition switch, either.

I forgot a good one that is always good for torn-out hair - female connector terminals with relaxed pins. They look fine but aren't actually making contact.

But first, find WHERE. For example, last week I had to diagnose why a truck's trailer brakes weren't working. Had voltage up in the cab, had no voltage in the 7-pin connector. Found a bulkhead connector under the truck - had voltage there. Move back. No more bulkhead connectors so I pierced the wire (don't worry, I resealed it) halfway back and there was voltage there... Eventually I found this hidden above the spare tire in a big wad of electrical tape:

And the lesson is: Be methodical and use scientific method in narrowing down your problem. And only complete berkheads use wire taps. The rest of the wires pulled apart with finger pressure even though most of them still made contact.

Your problem is of the same nature but reduced in scope - a voltage drop is a bad connection that hasn't failed 100% yet.

What size positive cable ? How is the battery grounded ? How is the engine grounded ? there must be complete circuit.

grounds are often the problem.

A bad ground is a voltage drop on the other side of the circuit But if he's seeing 11v with no starter solenoid in the circuit and 5v with it in the circuit, the problem is not in the grounds. Or at least the main problem is not in the grounds. There's a big chunk of resistance somewhere between the battery positive and the starter solenoid.

This is why I actually liked those old Haynes books. The wiring diagrams give you connector views and locations, and then there'd also be a diagram of where each connector was in-chassis. Sometimes getting this information is like pulling teeth.