Location of Flyback Diode

The inductance source is ... what? The starter?

 

I think you are preventing a non existent problem. in 47 years I have never seen an electrical failure of one of those ignition switches.

 

I've had a persistent problem with my 328 for years of turning the key and nothing happening (aside from some noise from the fuel injection unit) despite a full battery. When it does crank its fine but if its been sitting for a while its quite likely to misbehave. It can go for weeks & be absolutely fine & then it'll do it again. I've changed the starter relay & checked as many connections as I can find around the fuse board and in the loom but no luck.

I do recall reading somewhere that the starter activation is quite sensitive to voltage & one of the things I have in my car is an Alpine powerpack amplifier in line with the head unit. It occurred the other day that this might be causing a voltage drop because it powers up with the ignition, so I was thinking about putting a switch in line with the radio power feed to disable it & seeing if that helps.

I should also check that connector under the car first though though it has been apart several times over the years. I do need to get to the bottom of it because its irritating!

 

That's a solenoid. It's low load (switching a high load) so it's not significant.

 

My 328 did the no start" thing every once in a while and banging on the switch with my hand under the dash always "fixed" the problem. about five years ago I removed/disassembled/cleaned the switch and the no-start has never recurred.

 

I get the same noise which I think suggests that the ignition switch is OK because that noise only occurs when you crank the key to the start position. That would seem to point to either low voltage on the starter LT circuit (failing to trigger the starter) or a bad connection in the HT circuit (but I'm less inclined to think its that).

This sort of electrical gremlin is no fun!

 

I had a look at this today & I *think* I've fixed it.

The below for the benefit of anyone suffering a similar issue:

I came to the conclusion that the problem was on the LT circuit because when the starter failed to engage I could hear the fuel system whirring away, but no "click" at the starter - as you would get with a flat battery when you can hear the solenoid engaging but the motor won't turn over. So when it happened, there was no power to the starter on the LT circuit, or at least not enough to trigger it.

Nonetheless, because I could hear the fuel system activating it also said that the ignition switch was OK and passing current at the start position, so I left that alone.

The LT circuit (on a 328) is pretty simple - its a big fat white wire that goes down to a connector behind the passenger foot plate. From there it goes to the rectangular connector on the left side of the engine bay & from there down to the starter. Its very obvious which wire it is, its a much heavier gauge than anything else.

In my car someone (before my ownership) installed an immobiliser and there is now also a relay in the circuit in the passenger footwell beside the connector.

So I just cleaned all the connections & made sure the pins were a tight fit in the connectors and & replaced the immobiliser relay for good measure as well. I think the culprit was either the engine bay connector or a connection at the relay. I think the relay was OK but its a cheap thing to replace.

The starter engages every time now. There was also always a tiny delay even when it did engage & that is now gone too suggesting much better connections.

So it looks like it was a cheap and easy fix. If it reoccurs in the same way, then next stop would be the LT connection at the starter, or even the starter itself

 

This is the exact thing I have been experiencing on my 328 sporadically for a few months now. I too can solve the problem with a gentle tap near the key switch. Took me a while to pinpoint down to that area -- I originally was doing a Fonzie slap on the dash. I didn't want to go randomly picking at the wiring, so I was patient. My guess is the white wire connection at the key switch might need cleaning, so I'll start with that. If it doesn't solve the problem maybe contacts inside the switch need a cleaning.