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Re: Starter dead

PostPosted: Sun Sep 08, 2013 6:31 pm
by RogerFrench
Steve, I've sent you a PM.

Re: Starter dead

PostPosted: Sun Sep 08, 2013 8:48 pm
by billwill
Ah, I could not find the hand drawn one I did before, So I have redone a neater one.

BasicStartAndIgnition_ClassicCars.gif and
Basic Starter and Ignition Circuit of Classic Cars

Inside the starter switch, the moving contact is wide enough to connect simultaneously to TWO of the contacts.
In the normall running position it connects to the ignition circiut on the third terminal and to nothing on the second terminal.

But when you put the ignition key in the Start position the contact is also still connecting to the ignition circuit (the coil and contact breaker).

In the start position it connects 12v to the starter solenoid coil, which by magnetism sucks the big core iron bar upwards and causes the heavy duty copper contact to britdge the two fat terminals of the solenoid thus providing a heavy current path to the starter motor.

Re: Starter dead

PostPosted: Mon Sep 09, 2013 7:05 am
by JJDraper
Back to basics. The solenoid is a heavy duty switch supplying power to the starter motor. The switch is operated by electricity supplied by the ignition circuit as shown in the previous post. If the switch doesn't work, no power gets to the starter and it appears dead.

You have shown that the starter seems OK, and that the problem seems to lie with the switch (solenoid) not operating. The switch will fail to operate for one of two reasons; it has failed or it is not getting enough power to operate the electromagnet switch.

If the solenoid has failed, substitution with a working spare will solve the problem. If this cure fails, the problem lies elsewhere. I have been down this road!

Long story short, I have had two related issues in the past which gave rise to similar symptoms, both earth/poor connection based. Both times, the solenoid failed to operate, or gave a variety of squeaks, groans and clicky noises. Testing with a voltmeter showed a massive volt drop on the ignition circuit when I turned the ignition starter on. The volt drop was so great that the solenoid did not get enough power to operate cleanly.

In the first case, I tracked the volt drop down to a poor connection across a fuse on the ignition circuit - cleaned up fuse holder & the problem went away.

The second case was harder to track down, but was traced to a poor earth connection from the battery to the chassis (frame).

In both cases, the massive rise in current as the starter is engaged caused a poor connection to fail, leading to a non start.

Try connecting the battery via an additional earth strap, jump lead and/or cleaning up all contacts. Cheap & non glamorous but poor earthing/joints is at the root of the vast majority of electrical problems. Really weird symptoms are often down to earthing issues, as the power tries to find different paths to bypass a high resistance joint.


Re: Starter dead

PostPosted: Mon Sep 09, 2013 11:00 am
by billwill
Jeremy, Steve has already established that the battery earthing and engine earth strap are OK, because when he connects accross the fat terminals of the solenoid, the starter spins the engine.

Following on from that in a recent message, he says: "I tried checking the ground on the Solenoid using the multimeter but got no reading. " Unfortunate turn of phrase, because with someone not used to electric testing he might mean it reads 0.0 (which is good) or he might mean a blank screen or infinity indication, which would mean that the solenoid is not earthed.

Steve: The next step must be to get that solenoid properly earthed, or most subsequent tests will be invalidated or complicated by the fact that the solenoid cannot be operated.

Re: Starter dead

PostPosted: Mon Sep 09, 2013 11:19 am
by billwill

Test that you have mastered the art of finding bare metal connection on the engine, by putting your Ohm-meter probes on TWO such points on the engine and observing that you get a very low Ohm reading.

Then after you have fixed the earth wire for the solenoid and your Ohm-meter reads a low reading ( should be less than 1 ohm) between the solenoid case and the metalwork of the engine then redo the test which was on page 1 of this topic.

The medium thick brown wire is the feed from there (i.e from the battery) to the fuse box and onwards from there to all the other electrics.

The small terminal between the big cables is the actuating coil for the solenoid.

So all you need to do to test the solenoid is pull off the thick brown cable and the small cable on the centre connector then with care use a piece of wire about 3 inches long to tap between these two exposed contacts. On a working car that will close the solenoid and spin the starter (it won't start the engine because you disconnected the main feed to the ignition.

As AHM says, be very careful with that fa connector to the battery and the blade that you exposed pulling off the thick brown wire. That is a high current unfused connection direct to the battery. If you were to drop a spanner on it bridging to earthed metal it could MELT THE SPANNER... not kidding!!

If it clicks but the motor doesn't spin, because you have already established that the starter motor is OK, it implies that the connections inside the solenoid are dirty & you need a new one.

If it doesn't click you still have a problem in the earth of the solenoid or the solenoid is no good (coil burned out).


You won't get much further testing your circuits until you establish whether the solenoid is good or bad.

Re: Starter dead

PostPosted: Sun Sep 15, 2013 5:06 pm
by LoTex

Thanks again for all the suggestions. Here's the weekend update on the starter/solenoid/ignition issue:

Roger F lives about a 20 minutes drive from me and was kind enough to come out to have a look. Being a 3-Lotus man (and English) he has seen much of this kind of thing before. He spent the better part of 6 hours patiently working through the possibilities (while explaining to me what he was doing). He replaced the old solenoid with the new one and the engine turns over nicely now. He also changed out a number of frayed leads and grounds which may have been contributors to several fried wires (courtesy lamp, radio) which while not directly impacting the operation of the car clearly were not helpful to the cause. A previous owner had also done some not too nifty rewiring to add an Ampmeter and an separate temperature gauge and that was causing problems as well.

After all that, the ignition is still heating up when turned on so we think there is a short internally in the ignition switch. I'll get a replacement for that and do the install hopefully next weekend and report back.


Re: Starter dead

PostPosted: Sun Sep 15, 2013 7:22 pm
by billwill
Normally an ignition switch is not earthed, so it wouldn't normally be able to have a dangerous short circuit in it. (see my wiring diagram above, all exit wires do something), however what I expect has happened is that the contacts are burned and now high resistance, leading to hot contacts for the ignition current.

Re: Starter dead

PostPosted: Mon Sep 16, 2013 3:08 pm
by RogerFrench
billwill wrote:Normally an ignition switch is not earthed, so it wouldn't normally be able to have a dangerous short circuit in it. (see my wiring diagram above, all exit wires do something), however what I expect has happened is that the contacts are burned and now high resistance, leading to hot contacts for the ignition current.

I think you're right, with my multimeter I got connectivity, albeit with resistance, between the isolated terminals on the switch even with the switch in the "off" position. For example, when connecting the battery terminal, switch off, there's a slight click from the starter solenoid.

I really enjoyed my visit to Steve, it's nice to find and resolve some issues, though some remain. Just a bit frustrating to find one thing after another. To give an example of prior owner meddling, the starter switch Steve mentions in his first post was wired with that Amber-coloured transparent domestic flex often seen on bedside lamps. Such a shame in a great car!

Re: Starter dead

PostPosted: Mon Sep 16, 2013 4:32 pm
by billwill
Ouch, sounds like the ignition switch got really really hot at some stage and melted the contacts, so there is now no idea what connects to what.

And I have to retract my Nothing Dangerous... :o because power permanently to the solenoid actuation circuit is pretty dangerous even if as you say the resistance is too high to pull the solenoid in... because if it DID... the starter motor might engage while being driven fast and there would be bits of Bendix and teeth off the starter ring scattered everywhere.

Re: Starter dead

PostPosted: Sat Sep 21, 2013 8:57 am
by Pistacchio sprint 72
Humm i cheated because i did not install it myself. But i have now the high torque starter i bought from sjsportscars last year.
Geeez like in my super seven i think this mod really change life.
The starter cranck the engine all the way until it fires. No more whinning sound when the starter disengage...
Really happy with it.

Re: Starter dead

PostPosted: Sun Sep 22, 2013 5:16 pm
by LoTex
Hi Guys,

A lot of positive progress but still one issue.

I installed the new ignition switch this morning and was able to get the car running, first time in about a month. Good news in that neither the positive battery terminal nor the ignition switch got hot as was happening before.

However, after running the engine for about 2 minutes I noticed a small amount of smoke coming from the left side of the engine compartment. Roger, you may remember this particular wire, I think you tested it for continuity. It's a brown wire with a green tracer going from the wiring bundle to the fuse box, position 3 (lower left). I've attached a picture. This wire was definitely hot and although it was not totally clear that the smoke was coming from it (might have been from the exhaust headers below but I can't imagine why that would happen) I think that was it.

Any thoughts on what's happening now? This was not a problem previously.


Re: Starter dead

PostPosted: Sun Sep 22, 2013 6:22 pm
by richardcox_lotus
Are you convinced its the wiring ?? If the car hasn't been used for a few weeks - especially if its been up & down jacks or ramps, it's possible you've had an oil drip onto the exhaust.

1st time I had this I was somewhat concerned as well ( until I realised what the cause was...)

Re: Starter dead

PostPosted: Sun Sep 22, 2013 6:39 pm
by LoTex

Certainly a possibility that's where the smoke is coming from although it was never on a ramp, I did use my lift jack on both sides though. That still wouldn't explain why the wire was getting so hot-


Re: Starter dead

PostPosted: Sun Sep 22, 2013 10:46 pm
by billwill
The exhaust pipes will often smoke, when you restart an engine. In my case it is usually because some oil missed the hole in the cam cover when I was topping up the oil level.

My service manual is not on hand. What does it say brown with green tracer is used for?


The S4 wiring diagram says Brown with Green tracer is the main wire from the Dynamo to the control box. Even if you now have an alternator it is likely to use the same Brown/green wire.

When charging that does carry a lot of current and may get warm, but if it gets too hot it may be that there is something wrong in your dynamo (or diodes have blown in your alternator).

Re: Starter dead

PostPosted: Mon Sep 23, 2013 3:48 am
by RogerFrench
Good News! I am glad you got the car running - progress has been made!

For the benefit of readers, as well as Steve, the car has a dynamo, and a bunch of spurious wiring. While the smoke may be from the exhaust as suggested, I have my doubts.
The rewiring of the horn to the button on the dash, the substitution of an electric temperature gauge for the original, and the final resolution of some burnt wires all in my opinion need to be investigated. I'd be glad to come out again and help out.

I suspect dynamo / charging circuit, given that you told me your ignition light wasn't working, but I'd really rather not commit myself! It'll certainly be a lot easier to diagnose, now we can run the engine.