TM1820 Starter circuit

[Harry in Ky]

I'm only half way/sort of following this, but in the original post I thought I saw where someone "added a fuse to the ignition switch feed from the starter solenoid". Am I reading this correctly? There is a fuse between battery and ignition switch that's not factory? IF that's the case, my first thought is to change that. If you want a fuse in there, it should be AFTER the switch but before the ignition/accessory circuits. NOT involved in the start circuit. The start circuit can easily blow most any standard fuse in a heartbeat.

 

[pycoed]

But it's in the ignition feed, not the actual heavy starter circuit. i.e the wire that feeds the ignition switch & subsequently all accessory circuits. It has to handle supplying the solenoid switch current (about 10A apparently)until the engine starts & supplying accessory current thereafter. In theory a fuse here shouldn't blow unless something is wrong, which is the case here. I assume the previous owner fitted it because something WAS wrong & disconnected the start circuit, requiring two small wires to be touched to start it. I want to get the switch working again & to date have found the switch, the clutch switch AND the solenoid all to work individually but not together, which is EXASPERATING.

 

[Harry in Ky]

If it's in the feed circuit, it's still in the start circuit. Any power coming OUT of the switch (no matter where it goes) has to come INTO the switch first.

That's the wrong place for the fuse. And it's NOT just 10 amps to supply the solenoid. It's a great deal more. It only takes a second to blow the fuse, right?

 

[alexpops]

A normal key switch will have 4 terminals:
1. Batt+ (in from battery)
2. Run ( goes to ignition/accessories/fuse panel)
3. Start (to starter solenoid)
4. Glow (to glow plug relay)

The wire connected to batt+ will be heavier gauge than the others (10 or 12 awg vs 14 or 16 for run & depending on draw glow & start could be same 10/12, but usually 14/16 since only activating a relay -- same for big fuse panel ). The batt+ wire should come straight from the battery or run through the main fuse (100 amp). Did the previous owner change out the key switch to non-oem part? Did they wire it right if they had to take apart connectors?

Like Harry said, other than high amp main fuse, I've never seen a fuse in any part of the start circuit. Wires are upsized to handle the current. Shade tree stuff rigged wrong? Yeah throw fuses in to prevent a fire, but not in properly wired/designed oem wiring.

 

[ponytug]

But it's in the ignition feed, not the actual heavy starter circuit. i.e the wire that feeds the ignition switch & subsequently all accessory circuits. It has to handle supplying the solenoid switch current (about 10A apparently)until the engine starts & supplying accessory current thereafter. In theory a fuse here shouldn't blow unless something is wrong, which is the case here. I assume the previous owner fitted it because something WAS wrong & disconnected the start circuit, requiring two small wires to be touched to start it. I want to get the switch working again & to date have found the switch, the clutch switch AND the solenoid all to work individually but not together, which is EXASPERATING.

Given what you have reported, I would focus on two things;
1) the fuse to the ignition switch works in every position, except "Start", and
2) Applying +12V to the solenoid directly works.

I would suggest trying a new (even temporary) wire from the start wire at the ignition switch to the starter. If that works, then the problem is in the ignition switch to solenoid wire. If that doesn't work, then you need to either clean the switch out, and perhaps disassembly it to clean, or repair, the contacts, or just buy a new start switch.

I would be in favor of disconnecting the battery and perhaps giving the top of the solenoid a good cleaning. File it under the "it can't hurt" category. Perhaps I'm being overly sensitive to the damp and humidity in west Wales, but it comes of experience in similar climes.

All the best,

Peter

 

[Harry in Ky]

Given what you have reported, I would focus on two things;
1) the fuse to the ignition switch works in every position, except "Start", and
2) Applying +12V to the solenoid directly works.

I would suggest trying a new (even temporary) wire from the start wire at the ignition switch to the starter. If that works, then the problem is in the ignition switch to solenoid wire. If that doesn't work, then you need to either clean the switch out, and perhaps disassembly it to clean, or repair, the contacts, or just buy a new start switch.

I would be in favor of disconnecting the battery and perhaps giving the top of the solenoid a good cleaning. File it under the "it can't hurt" category. Perhaps I'm being overly sensitive to the damp and humidity in west Wales, but it comes of experience in similar climes.

All the best,

Peter

I believe we're seeing this differently. My impression is the fuse and ignition switch work as expected UNTIL the switch goes to "start". That's when the fuse blows. The solenoid and starter work fine as long as it's NOT supplied through the fuse. Maybe I got it wrong.

 

[ponytug]

I believe we're seeing this differently. My impression is the fuse and ignition switch work as expected UNTIL the switch goes to "start". That's when the fuse blows. The solenoid and starter work fine as long as it's NOT supplied through the fuse. Maybe I got it wrong.

Actually, I think we are on the same page, I think that I may have just explained it poorly.

The previous bypass of the ignition switch was from the battery to the solenoid directly, at least as I understood it. To my way of thinking, that leaves both the wire from the switch to the starter (or the connector/terminals) and the switch as potential issues.

If @pycoed were to run a temporary wire from the switch to the solenoid that could test whether the existing wire is the issue, and if the temporary wire fries the fuse, then the issue is at or in the ignition switch. I leave open the possibility that the start wire is shorting at the switch.

BTW: @pycoed a 10ga wire is 5.2mm2, FWIW...

Sorry for not explaining it well the first time.

All the best,

Peter

 

[Harry in Ky]

No, we're not. Bypassing the switch to solenoid wire still relies on the feed wire with the fuse. Bypassing everything and going from battery to solenoid does NOT blow the fuse because it's not using the fuse.

 

[pycoed]

Actually, I think we are on the same page, I think that I may have just explained it poorly.

The previous bypass of the ignition switch was from the battery to the solenoid directly, at least as I understood it. To my way of thinking, that leaves both the wire from the switch to the starter (or the connector/terminals) and the switch as potential issues.

If @pycoed were to run a temporary wire from the switch to the solenoid that could test whether the existing wire is the issue, and if the temporary wire fries the fuse, then the issue is at or in the ignition switch. I leave open the possibility thatthe t the start wire is shorting at the switch.

BTW: @pycoed a 10ga wire is 5.2mm2, FWIW...

Sorry for not explaining it well the first time.

All the best,

Peter

Yeah - I agree with all that. I'll try a new wire from terminal C to the solenoid & see if the fuse blows. Just to avoid misunderstanding, I attach the following sketches showing (Start1) what should be in place

& (Start2) what was in place when bought.

I'll be quite happy to ditch the extra fuse once I knew the problem that must have led to the PO fitting it has been fixed. Until then it might will save loom damage.

 

[pycoed]

If it's in the feed circuit, it's still in the start circuit. Any power coming OUT of the switch (no matter where it goes) has to come INTO the switch first.

That's the wrong place for the fuse. And it's NOT just 10 amps to supply the solenoid. It's a great deal more. It only takes a second to blow the fuse, right?

I'm thinking that the pull-in coil in the solenoid is drawing too much current & blowing the extra fuse before the reduced hold-in current is applied. What troubles me is WHY they put in the fuse in the first place. Solenoid & starter work perfectly with jury rigged wires, just not with the factory setup