Booster solonoid

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pcatterall

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Or booster for the solonoid. The lead to my starter solonoid seems, at one time to have gone straight to the solonoid, it seems to have then been cut at some time and routed to a 'unit' at the other side of the engine then back to the starter. My electrician says this may be 'booster' what does this do?? (up the volts or what??)
Thanks Peter
 
Are you referring to the lead from the starter switch on the control panel? If so, one possibility is that a relay was fitted. The switch closes the relay, which then feeds the starter solenoid direct from the battery. The switch therefore only handles the relay coil current. Similar arrangements can be used for the heater plugs and stop solenoid. Mainly useful to reduce voltage drop if there is some distance between the panel and the engine and battery at the expense of some complication.
 
Thanks for the ideas to date. It is the lead from the control panel. The unit concerned could be a relay I suppose but the lead is the same section ( 1.5 or 2mm say) from the control panel to the 'mystery unit' and from there to the starter. The lead from this unit to the starteris just as long as it would be to come straight from the control panel so it seems pointless to have it there at all.
Depending on further advice perhaps I should chop it out as part of excercise in simplifying and chopping out redundant wiring??
Regards peter
 
If it is a relay for operating the starter solenoid there will be four connections (although there could be other unused terminals)

One will come from the starter switch on the panel
One will be earthed (or at least go to negative)

One will be a supply from the battery
One will be connected to the small terminal on the starter solenoid

The first two are the connections to the coil the second two the contacts.
 
Ah, but, Philip my comment was pending further advice!!
There really are a lot of wires which dont seem to do anything and have themselves been by passed over the years, perhaps I should just go back to basics and start again it is after all just a diesel engine with a starter and an alternator plus oil and water sensors.
 
It is possible that this booster solenoid was fitted because the contacts of the start switch were dicky. (and not because of volt drop in the wiring)
A start solenoid can take 5 amps or even more to activate it, especially the types that shove the pinion into mesh as well as make a contact to power the starter. A booster relay (solenoid) will take more like a 1/4 amp and so is a lot kinder to the start switch contacts or doesn't require such good contact. The booster relay will often operate happily at down to 8 volts. Allowing for bad switch contacts.
It may have been a more economical modification than cost of replacement start switch.
So if you want rewire the start switch direct to the start solenoid and see how it goes. If operation is unreliable then it was probably done to allow a bad start switch to work ok. good luck olewill
 
I was only being careful.

I'm a marine electrician (retired from MN) and it is always difficult to sort out old wiring. I have the same problem on my boat, and I am slowly getting it sorted out. I had the same problem when on containerships, trying to find faults where some new equipment had been fitted, and some of the old (unused) wiring was left behind.
 
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