I'm having a bit of a strange problem with my 99 ls400. Before I start, I have checked all electric components and the battery, alternator, starter relay, main relay, and all grounds are good. The problem I've run into is a small black connector on the starter unit itself. I'm not too sure what it is, but my best guess is something related to the ignition? When bench testing my starter, the teeth extend and spin perfectly fine, no problems there. However, I find that if i do not connect the positive lead to the black connector via a screwdriver, the starter only extends and does not spin-the same symptom I have when the starter is mounted on the car. I cannot see where this wire leads to, as there is virtually no space behind the block to see or even feel around. Does anybody have a clue as to what this piece could be, and how I could fix my no start issue?

 

It looks like a connector to the plunger coil.

 

The signal at the black connector is the starter control signal & it's tied to the ignition. When you crank the engine by turning the ignition key, 12V (low current) is sent to the starter's solenoid which will energize the solenoid's internal electromagnet then the 12V (high current) from the battery is routed directly to the starter via the heavy gauge power cable & caused the starter's pinion to move out & engage w/ the flywheel. This in turn will crank & start your engine. The way you stated your problem wasn't clear & accurate but here's the answer anyway: When you bench tested the starter, you're testing it w/ an open circuit which means there's no load at the output of the starter & there was indeed 12V applied to the pin at the black connector, that's why you were able to see the starter's pinion moved & spun freely. However, when you had the starter mounted back into the car, when you've tried to crank & start the car, the starter was loaded down by the engine via the flywheel that's why you stated the pinion only moved out but couldn't spin. I suspect 1 of the 2 copper's contacts/terminals inside your starter's solenoid has worn out so when the starter is loaded w/ a heavy load (engine), the plunger inside the solenoid couldn't provide a solid connection for the 2 contacts/terminals thus no 12V (high current) from the battery was present at the starter. You have the option to replace the entire starter/solenoid with a new one or just replace the 2 copper contacts/terminals & plunger inside the solenoid. If you opt for the 2nd option, you can buy the starter solenoid repair/rebuilt kit at the dealer or online. Due to the placement of the starter/solenoid in our Lexus LS400's, most people have opted for option1 as it has given us a peace of mind just in case there may be a problem w/ the electric starter motor later on down the road.

 

I took another look at your photos & the starter appears to be new so if it is then I may have misunderstood your problem statement. If that's the case then check your starter control signal. Have someone turn the ignition key then check to see if 12V is present at the black connector. If it's not present then there's a broken connection somewhere between the ignition key's switch & the black connector (broken wire or bad connector/pin). If 12V is present then you have a faulty starter/solenoid & most likely it's the solenoid as I have stated previously.