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Starter Circuit woe. Help needed

Glad it’s sorted John.
It does make faultfinding interesting not having drawings but it’s so much easier with them.
 
Not so sure about interesting- but time consuming, frustrating and slow certainly. I'd still be at it without your imput though.
Cheers.
 
Haha… I’ve always loved troubleshooting and I often have to troubleshoot machines I’ve never seen before. Sometimes with no drawings.
I must say I’m less keen on car electrics as the darn things don’t stand still, vibrate like crazy and have mostly hidden or taped up wiring.
 
And finally, having fitted the later starter specified for late 1995 onwards I was struck by a thought.
The original starter was 24V on both circuits with the actuator fed through the starter relay from a fusible link attached to the starter battery positive. The late 1995 onwards 80s wiring eliminated the starter relay, with the starter actuation circuit fed 12V direct from the ignition switch.
As my 80 stands at the moment the late specification starter is getting 24V for actuation from the starter relay. I've not used the car much since fitting the starter and there are, so far, no signs of ill effects from over voltage. I've moved the fusible link connection to the negative side of the starter battery so it sees just 12V when the starter is operated, which makes no observable difference.
I am having some trouble beleiving that Denso went to the trouble of making a unique starter for the later 80s to operate on two voltages and I am now searching to see if the same starter is specified for the later Coaster bus, which is 24V only. Anybody got any light to shed on this?
 
Could be a 12v coil and overdriving it by 100% for the tiny time it takes to start is not going to harm it in the short term. If it works well on 12v sounds like it’s job done, no need to worry about anything else.
 
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Well you say I shouldn't worry but I hate leaving things I don't understand. Although I said I had connected the fusible link that feeds the starter relay to the negative terminal of the starter battery I hadn't actually done it then but I used a temporary wire from the other battery. Actually when I got round to wiring it properly to the negative of the starter battery it didn't work, and it prevented the 12/24 changeover relay working too.
The reason must be in the workings of voltage converter timer which led me to trying to understand the theory and practice of the timer. After much thought and head scratching I haven't a clue what problem the timer is solving or what it is intended to do that couldn't be achieved by operating the voltage converter with the starter relay.
Any explanations anyone?
 
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I think you could be overthinking this John.

If your starter is 12v on the solenoid coil and is receiving 24v and its a problem, you could either swap the starter for the correct one, replace the coil for the correct voltage, fit a current limiting resistor of suitable size and rating or leave it as it is.
 
I have absolutely no doubt that I am overthinking the whole business but I do go to some pretty remote places and the more I understand about how the 80 works the more confident I feel that the solution to any problems won't involve a lot of walking; so I like to know what things do and why. Incidently, I am beginning to think that the post 1996 wiring diagrams that are available may be all American market versions which are petrol, 12v and don't have a starter relay. I don't know anybody with a later diesel to poke my nose into but in the meantime I think I'll stick with treating the 1996 starter as a full 24V starter with 24V on both circuits, unless anyone knows different.
 
upload_2018-11-19_12-0-24.png

I looked up the starter on the HZJ75 and the parts# matches with the nummber on the denso starter I pulled from my 97 80-series.
 
Yes Firewart, that was part of my problem. The OEM starter pre 1996 with the post type actuator connector is only available, so far as I could find, in Chinese copies or from Toyota at eye watering prices. ($1733 from Amayata) I bought a genuine Denso DSN1228 specified for 1996 onwards for £175 (which is what your '97 80 should have had on it). This has a spade connector for the actuation circuit so I altered the wiring to suit with a late model wire from a scrapper. At this point I had only copies of wiring diagrams which showed the starter being actuated direct from the ignition key in post 1996 80s with no starter relay. I now realise that all these diagrams are for US petrol based vehicles and having found the EWS supplement for post Aug 96 HDJ80s I am relieved to find that the diesel starter needs 24V on both circuits so I can just use the existing circuit from the LH battery fusible link. Problem now solved to my satisfaction!
No nearer though, in understanding what the little computer that controls the 12/24 changeover does; though, as it senses the alternator warning light, I assume one function is to protect the alternator from 24V if the relay sticks. Still waiting for a forum expert to tell me, or hazard a guess.
 
There is no computer for starting. There’s a changeover relay that puts the batteries in series for starting on the second key position, controlled by a timer so if doesn’t sit there at 24v all day. The alternator volt sense contact is also disconnected while this relay is energised. When the key is turned to start voltage is applied to the starter through the start relay contacts. That’s all there is to it really. :)
 
OK. But if that's all it does why make it so complicated, and what is it timing. When you start the ignition switch powers the starter relay and the "timer" at the same time. (it also tells the glow plug computer and the AC as I would expect) I could understand making a short delay before actuating the starter so that the 12 to 24 changeover didn't happen under load to reduce arcing but it doesn't seem to do this, though perhaps it does this at the end of the starting cycle, delaying the changeback until the starter is disconnected. According to one wiring diagram I've seen the connection from the timer to the alternator goes to the L connector not the battery sense (S) connector. Another diagram showns a "24V hold warning relay" connecting the "CHARGE" fuse to earth, which I find confusing! Any idea if/how the "24V hold warning" is shown to the driver?
 
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