Fiat TC 1756 Wiring for starter solenoid - help please!

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twincamspit
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Fiat TC 1756 Wiring for starter solenoid - help please!

Post by twincamspit » Sun Sep 25, 2011 10:23 pm

Hello all,
Apologies for this, but I've spent days trawling the internet and various Fiat forums and not been able to find what I need.

Can anyone direct me to adiagram, photo or explanation of how I wire up the starter/solenoid on a 1977-registered Fiat 132 (1756cc)?

I have moved house several times since the wiring and engine were separated, and now it's time to wire it up I can't find my notes on which lead goes where! And the Haynes book doesn't help.

There is a large, heavy green lead with a ring connector at one end, and a battery terminal on the other. Also attached to this is a thinner brown lead with a smaller ring terminal. I recall that this was attached to the positive battery terminal, and I assume that the brown lead is the 'feed' for the fusebox for everything other than the starter.

There is also a thinner pair of leads, one black with a ring terminal, and the other red with a female spade terminal.

The red lead is not a problem, as it can only fit onto one place on the solenoid.
However, I am at a loss to where the other leads go. There are 2 heavy threaded 'post' connectors on the solenoid.
Does the black ring terminal go to one, and the heavy green lead go to the other?
If so, does it matter which way round?

Also, which lead (red or black) is the positive 'trigger' to activate the solenoid please?

Sorry if this is an overly simple question to you experts, but I'm seriously frustrated at not being able to make sense of this with my multi-meter and haynes manual!

Richard (twincamspit)
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Guy Croft
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Re: Fiat TC 1756 Wiring for starter solenoid - help please!

Post by Guy Croft » Mon Sep 26, 2011 10:17 am

Do me a favor (save me having to) and post a photo of the relevant end of the starter and I will tell you how to hooki it up.

G

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Re: Fiat TC 1756 Wiring for starter solenoid - help please!

Post by twincamspit » Mon Sep 26, 2011 8:28 pm

Hello Guy,

Thanks for looking at this I appreciate it.

The photos are attached (hopefully) below. They're a bit rushed and rough due to work commitments, but hopefully sufficient for you to determine the type. The Haynes manual says that the 1.6 and 1.8 (mine) use a Fiat 1.3 KW starter, the 2.0 and Argenta use a different one, although I'm sure you already know that!

Starter is embarrasingly grubby; the whole engine is going to have a thorough clean and paint touch up once I prove it still runs.

Richard (twincamspit)
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twincamspit
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Re: Fiat TC 1756 Wiring for starter solenoid - help please!

Post by twincamspit » Mon Sep 26, 2011 8:32 pm

sorry, forgot to mention - please ignore the wiring on these photos, it's wrong!
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WhizzMan
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Re: Fiat TC 1756 Wiring for starter solenoid - help please!

Post by WhizzMan » Tue Sep 27, 2011 9:20 am

In general, on the vast majority of cars, there are two terminals on a starter. One goes to the positive of the generator/alternator and is also connected to the battery positive. These are big fat leads, since the starter and generator work with high currents. This way, you only have one lead coming from the battery, "touching" the starter and then continuing to the battery. This is alway 12V, even with ignition off. Do not connect the battery end until the other ends are properly bolted on, or you risk a short of a very thick, unfused lead.

The other terminal is usually set up with a smaller gauge wire. This is the "signal" lead for the solenoid to activate. The solenoid then triggers a switch to power the starter motor and it also throws the little gear on the shaft of the starter motor on the gears on the fly wheel. As soon as you stop cranking, a spring inside pulls the little gear back in a "neutral" position and the starter motor switch is also switched off.

Negative for both leads comes from the engine itself. The engine itself therefor should be ground to either the chassis or the negative terminal of the battery.

With this generic description you should be able to figure out yourself which lead goes where, I hope?
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Re: Fiat TC 1756 Wiring for starter solenoid - help please!

Post by Guy Croft » Tue Sep 27, 2011 10:04 am

I've taken out all but the best of your pics.

Wiring picture which I trust is in accord with what has been written above...

G
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twincamspit
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Re: Fiat TC 1756 Wiring for starter solenoid - help please!

Post by twincamspit » Tue Sep 27, 2011 9:52 pm

Thanks Whizzman, that is a nice clear description and pretty much agrees with what I thought I understood about relays/solenoids and starters generally.

What didn't seem to make sense was the lack of a circuit between the heavy terminals once the solenoid was activated.

I'd established that the lower heavy terminal (which goes to the starter) is earthed to the engine/chassis, whereas there was no circuit
from the upper heavy terminal to the body.

I suspected that the red was the 'trigger' +12V to activate the solenoid, so I tried an experiment with minimal wiring of:
The heavy (green) wire to positive battery (via a 12V lamp) at one end and onto the upper heavy solenoid terminal at the other, plus
The red "trigger" wire to the only place it can go on the solenoid, the spade connector.

With the solenoid not activated (i.e. no +12V supply to the red trigger) there was no circuit across the heavy terminals, as expected.
However, with the solenoid activated (i.e. +12V supply to the red trigger) there was a satisfying "clunk" from the solenoid - yet still no circuit across the heavy terminals.

This unusual result, along with the "left over" brown and black cables left me feeling uncertain of how it should be wired, hence my search for a definitive description or diagram!
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twincamspit
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Re: Fiat TC 1756 Wiring for starter solenoid - help please!

Post by twincamspit » Tue Sep 27, 2011 10:04 pm

Guy Croft wrote:I've taken out all but the best of your pics.

Wiring picture which I trust is in accord with what has been written above...

G
Thanks Guy, appreciate your feedback.

Although it can't be seen in that photo, there is another black lead between the solenoid and the starter, very close to the lower post
that you labelled "B". The black lead that you can see in the photo, rather misleadingly, is a different black lead with a ring terminal, and I think that's why you labelled that one as "goes into motor (or should do)"! Sorry about that, it's obviously not easy to take a decent photo without removing the mechanical fuel pump or removing the starter, neither of which I had time to do.

So the solenoid 'B' post only has the "inbuilt" connection down to the starter, I understand that.
The red is the activating / trigger supply from the switch, thanks for confirming that (thought it might be).
And the heavy green lead goes to "A" and onto the battery, great.
Presumably, from what Whizzman said, there should also be a connection from here to the alternator, also of significant thickness?

I think the brown lead that is joined to the green at the battery terminal end is too thin to be the feed from the alternator to be honest,
so I'll probably wire up a second heavy connection from the alternator to the "A" post separately, and use the brown to feed the fusebox.

The thin black lead doesn't seem to be needed by the sound of it.

This now makes me wonder if there's something wrong with my solenoid (even though it clunks nicely), because as I said to Whizzman, there is no circuit between the heavy terminals when +12V is supplied to the red activating lead.

Or, just as likely, I've missed something?
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Re: Fiat TC 1756 Wiring for starter solenoid - help please!

Post by WhizzMan » Wed Sep 28, 2011 6:52 am

The starter motors I've seen so far, with the only exception of a pre WW-II one, have the "clunk" make the connection to the starter motor internally, from the big positive terminal. The solenoid does two things, engage the gear and switch on the power to the starter motor. The Pre WW-II one had a pedal replacing the electro-magnet in the solenoid, but still had the switch "internally". I don't know if this starter motor is an exception to the above, but it sounds much more logical that your starter motor has developed a problem. If anyone could confirm or clarify what system is used here, you should be able to get this puzzle solved.
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Re: Fiat TC 1756 Wiring for starter solenoid - help please!

Post by Guy Croft » Wed Sep 28, 2011 9:46 am

briefly -

nothing should be connected to 'B' (excepting that some models have a cable to the motor from that point). Any ancillaries must be connected to 'A' because that is the only permanently live +ve connection on the motor.

'B' is only live when you activate the starter so if you have anything else on there I'd gure it's wrongly wired.

G

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Re: Fiat TC 1756 Wiring for starter solenoid - help please!

Post by Urbancamo » Wed Sep 28, 2011 11:02 am

Hi Richard;

You have obviously cleared thru wiring, there should be only 2 wires on the starter (and +1 which goes inside starter motor)

If your solenoid clunks but starter won't turn, you either fave fault on the solenoid or motor itself. Do you have tested started outside of the car?

If your B-terminal doesn't show voltage when starting, obviously solenoid doesn't let thru anything even if it clunks. It may have burned points. Solenoid is very simple device. It's basically a relay, but with high current capacity.
IMG_4496.jpg
Typical Fiat-family solenoid disassembled. You can see terminals on the left. When ignition is turned on, coil magnetizes and hits big plate to the terminals and lets current to flow to starter motor.
IMG_4496.jpg (37.93 KiB) Viewed 3946 times
On old cars like this it's vital to check also engine-body ground connection. Where ever it's found, i don't know exactly where it is in this specific Fiat 132.
Poor ground connection leads to very odd problems, and usually problems starts when high current is used, like starting an engine.

T
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twincamspit
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Re: Fiat TC 1756 Wiring for starter solenoid - help please!

Post by twincamspit » Thu Sep 29, 2011 12:58 pm

Hello again,

Thanks for the extra information and the photo.

It certainly sounds like there's a problem with the solenoid itself, so I think I'll try an external one with the output to the 'B' post so that it goes live when the external solenoid is activated.

I've got an old external one kicking about anyway, as the 132 engine and box are actually in a Triumph Spitfire rather than the original Fiat body, and the Spitfire used an external relay.

Should anyone else find this post due to similar confusion with their TC, I now have a photograph of a Fiat 124 spider's starter and solenoid, which although earlier than my '77 Fiat 132 is a very similar setup (it certainly fits the descriptions of wiring from both of you), see attachment.

Thanks again,

Richard
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Re: Fiat TC 1756 Wiring for starter solenoid - help please!

Post by TomLouwrier » Thu Sep 29, 2011 1:25 pm

hi Richard,

I'm still not entirely clear on the connection between the relay (post B) and the motor. That should be pretty short and fat connection, usually not even wire but a solid copper strip going straight into the casing. In size and shape not unlike the tag that I see over your thin black wire(s?).

Keep in mind that you may be able to test the starter with an external relay, you could do that just as well by clamping a jump start lead on terminal B and then pushing the other end onto the battery's plus. It wil spark a bit, but you should hear it hum. However, it will not start the engine, see below.

A starter that was designed with an integral relay can not be run off an external relay!
The old Lucas item originally fitted to the Spit uses an inertia-activated pinion, that comes out as the starter spins up. They tend to get stuck and then you just get a click and a hum, but no engagement. No joy...
The Marelli item on the Fiat engine uses the solenoid to first slide out the pinion into the ring gear, then switch on the starter motor. You see that you need the integrated relay to connect the starter and the flywheel.

Pull that starter and get it on a bench. You're giving yourself a hard time by trying to avoid it.

regards
Tom
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twincamspit
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Re: Fiat TC 1756 Wiring for starter solenoid - help please!

Post by twincamspit » Thu Sep 29, 2011 2:18 pm

> "Pull that starter and get it on a bench. You're giving yourself a hard time by trying to avoid it."

I think you're right Tom, it'll have to be done. It was just a long-shot that I'd simply wired it wrong!

So my idea of using an external solenoid to simply provide a heavy supply to the B post on the solenoid isn't going to work; your reasons fit in with the last post from WhizzMan too, i.e. "The solenoid does two things, engage the gear and switch on the power to the starter motor."

I'll remove the starter and solenoid and take the solenoid apart initially.

Thanks everyone for the info, at least I've more of a clue what it should look like now.
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