Troll Hunter Posted January 13, 2023 Share Posted January 13, 2023 Hi, All, The vehicle is a 1991 Defender 110 CSW in middle east spec. which originally had a 3.5V8 but now has a 300Tdi You can tell from my earlier requests for help that I'm no expert in electrickery. I now have another question that I need help with. In the rat's nest of old wires from behind the dash there are three Pektron A75-294 diodes. The old wiring doesn't give any clue what they were for since none are connected close to any component and each seems to have multiple wires connected to it. Also, cable colours do not give any sensible clues! I'm assuming that they are all flyback diodes, but what circuits were they protecting, and are there only three circuits that need protecting? Or can a single diode protect multiple circuits? I've not seen this in any of the Youtube vids I've watched. I understand that a flyback diode is required on inductive circuits, and those I've been able to identify are: - Starter solenoid - FIP solenoid - Cabin heater fan motor - Starter motor - Ignition coil - from original motor - Alternator - Rear window Wiper motor - Windscreen wiper motor And I'm sure that I've not identified some😕. So, if anyone with the necessary linked-up grey cells can enlighten me I will be very thankful. Mike Quote Link to comment Share on other sites More sharing options...
western Posted January 13, 2023 Share Posted January 13, 2023 Some info here Quote Link to comment Share on other sites More sharing options...
Troll Hunter Posted January 14, 2023 Author Share Posted January 14, 2023 Of course, I did forget some items. What about the two screen wash pumps, one for the windscreen and one for the back window, and what about all the relay coils? Do these small current users require protection with a diode? Mike Quote Link to comment Share on other sites More sharing options...
western Posted January 14, 2023 Share Posted January 14, 2023 No diodes in the washer pump circuits or in relays, except for the voltage sensitive switch (yellow case) that stops the rear screen heater being on when ignition is off. Quote Link to comment Share on other sites More sharing options...
monkie Posted January 14, 2023 Share Posted January 14, 2023 This is the only circuit containing the diode you mention that I found in my wiring loom on a 1988 2.5TD 110. As Western says, it is in the heated rear window circuit. Quote Link to comment Share on other sites More sharing options...
western Posted January 14, 2023 Share Posted January 14, 2023 I will have a look in my Defender wiring diagrams but pretty sure there are only 3 in the system Quote Link to comment Share on other sites More sharing options...
Troll Hunter Posted January 14, 2023 Author Share Posted January 14, 2023 OK, that's one accounted for, although I don't understand how it works in the VSR. Damn electrickery! Thank you, monkie. I've identified the section of wiring from the alternator to the battery, including the section to the no charge warning bulb. This section is intact and includes the resistor, but does not include a diode. As far as I can tell from the wiring sections the fuel shut-off solenoid does not have a connection to the alternator. So what are the other two for? Do any of my list of suspects qualify? Mike Quote Link to comment Share on other sites More sharing options...
monkie Posted January 14, 2023 Share Posted January 14, 2023 It's been a while since I looked at the wiring. I'll double check all my notes and drawings for you that I made when I rewired my 110. I don't recall any more than 1, but I'm starting to doubt myself (also my original wiring was a right mess of previous DIY jobs since 1988, so maybe others were deleted by previous owners?) Quote Link to comment Share on other sites More sharing options...
western Posted January 14, 2023 Share Posted January 14, 2023 3 hours ago, western said: I will have a look in my Defender wiring diagrams but pretty sure there are only 3 in the system Can only find one on my wiring diagrams item 9 in the attached diagram Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted January 14, 2023 Share Posted January 14, 2023 I doubt in automotive any of them are being used as flyback protection as there's no sensitive electronics in a Defender that would care about a flyback pulse. They're probably used as "one way valves" which is more common, as others have said they crop up on the charge light circuit to stop the alternator warning light back-feeding into the ignition live and keeping the stop solenoid from actually stopping. A picture or list of connected wire colours might help. Quote Link to comment Share on other sites More sharing options...
monkie Posted January 14, 2023 Share Posted January 14, 2023 12 minutes ago, FridgeFreezer said: They're probably used as "one way valves" which is more common, as others have said they crop up on the charge light circuit to stop the alternator warning light back-feeding into the ignition live and keeping the stop solenoid from actually stopping. This rings a bell. I had this very problem a few years ago before I did the rewire. It wasn't 12v leaking back, but just enough to prevent the solenoid from closing so I had to stall the engine to stop it. I think I had a thread about it... Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted January 14, 2023 Share Posted January 14, 2023 11 minutes ago, monkie said: It wasn't 12v leaking back, but just enough to prevent the solenoid from closing so I had to stall the engine to stop it. I think I had a thread about it... It's 12v on the other side of the warning light divided by however many milliamps it takes to keep the stop solenoid holding on! Same thing with V8 EFI conversions, if the ignition is run from a relay rather than direct from ignition live you only have to back-feed enough to hold a relay closed and the truck won't turn off Quote Link to comment Share on other sites More sharing options...
Troll Hunter Posted January 14, 2023 Author Share Posted January 14, 2023 14 minutes ago, monkie said: This rings a bell. I had this very problem a few years ago before I did the rewire. It wasn't 12v leaking back, but just enough to prevent the solenoid from closing so I had to stall the engine to stop it. I think I had a thread about it... You did, on 1st January 2019. It's one of the threads that western included in his reply. Mike 1 Quote Link to comment Share on other sites More sharing options...
Northwards Posted January 14, 2023 Share Posted January 14, 2023 My car is a 1994 300Tdi, so a bit later, but I think there's a diode somewhere in the brake light circuit/handbrake light. Quote Link to comment Share on other sites More sharing options...
monkie Posted January 14, 2023 Share Posted January 14, 2023 2 hours ago, Troll Hunter said: You did, on 1st January 2019. It's one of the threads that western included in his reply. Mike I didn't even notice that was mine! 1 Quote Link to comment Share on other sites More sharing options...
western Posted January 14, 2023 Share Posted January 14, 2023 3 hours ago, Northwards said: My car is a 1994 300Tdi, so a bit later, but I think there's a diode somewhere in the brake light circuit/handbrake light. 2 in the 300tdi wiring diagram, 1 between handbrake wire to dash warning light & 1 in transmission overheat wire to dash warning light, none in brake light circuit. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted January 15, 2023 Share Posted January 15, 2023 Worth saying that for small loads a bog standard 1N4001 diode (50v/1A max) would be perfectly fine, for larger stuff just step up the range, for most applications I can imagine in a Land Rover it's not going to be critical and almost any diode with a suitable rating should do. Quote Link to comment Share on other sites More sharing options...
Sigi_H Posted January 15, 2023 Share Posted January 15, 2023 I can remember, I had diodes in my air condition circuit. Maybe the compressor clutch. Was a V8 before as well. Quote Link to comment Share on other sites More sharing options...
Troll Hunter Posted January 16, 2023 Author Share Posted January 16, 2023 Thank you, all. It's slowly coming together. Since my vehicle was originally a V8 with air-conditioning, there may well have been a diode(s) in the A/c system, now gone, as Sigi_H suggests, and since it was first registered in Kuwait it may have been to Saudi spec, as shown in the 300Tdi Electrical Circuit Diagrams, and it has got a HRW, which accounts for another one, both identified by western. Thank you, western. The 300Tdi Electrical Circuit Diagrams also shows a diode in the brown/yellow lead to the alternator. So, having identified five possible locations for diodes, are there any of the locations in my earlier list that would benefit from a diode, primarily to reduce arcing at the switch? If nobody (FF) comes back with recommendations I'll stick with the HRW, park brake and alternator locations. Mike 1 Quote Link to comment Share on other sites More sharing options...
Sigi_H Posted January 16, 2023 Share Posted January 16, 2023 This had been the relays for the air condition I removed incl. the diodes Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted January 16, 2023 Share Posted January 16, 2023 7 hours ago, Troll Hunter said: are there any of the locations in my earlier list that would benefit from a diode, primarily to reduce arcing at the switch? I've never seen it done by LR or anyone else, some automotive relays have a diode across the coil but I suspect that's either for radio interference or to protect an ECU that's switching it. I doubt any LR switches would really care. Quote Link to comment Share on other sites More sharing options...
Troll Hunter Posted January 16, 2023 Author Share Posted January 16, 2023 Thanks for the reassurance, FF. I'll ignore all the items in my previous list. Hi-Fi radio in my LR is not a possibility, let alone an objective, so the occasional interference will not be a problem. Thank you, again, to everybody who has contributed to this thread. Mike 1 Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted January 17, 2023 Share Posted January 17, 2023 14 hours ago, Troll Hunter said: the occasional interference will not be a problem It would only ever be a brief click or pop when switching something on or off anyway. Quote Link to comment Share on other sites More sharing options...
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