JST Posted October 31, 2007 Share Posted October 31, 2007 OK, i got one of these timers from Western, PRC 6796, 5 pin which is for a rangie heated front screen. i am fitting it to a '99 td5 defender Ralph kindly sent through some electrical diagrams with it but i still cant work it out. Firstly is this a combined relay and timer or just a timer? Secondly how would i wire it up for either of the above two outcomes? there is no continuity across any of the terminals. Quote Link to comment Share on other sites More sharing options...
western Posted October 31, 2007 Share Posted October 31, 2007 Found that this is used on Defender from VIN 2A622424, which I believe is from 2001 onwards [nothing in my Td5 1999 info] hth glad it got to you safely Quote Link to comment Share on other sites More sharing options...
MPS4X4 Posted October 31, 2007 Share Posted October 31, 2007 I have a wiring diagram that I made up using loom from a RRClassic I have listed part numbers of loom, relays switch and timer relay used. I have used this in the past as I fitted heated screen to a 90 of mine about 10 years ago. Email me at mps4x4@mac.com and I will e-mail you the diagram as I cannot figure how to put it in a post. Simon Quote Link to comment Share on other sites More sharing options...
JST Posted October 31, 2007 Author Share Posted October 31, 2007 email sent Quote Link to comment Share on other sites More sharing options...
MPS4X4 Posted October 31, 2007 Share Posted October 31, 2007 PRC6796 is the timer relay. Simon Quote Link to comment Share on other sites More sharing options...
JST Posted October 31, 2007 Author Share Posted October 31, 2007 Simon, thank you very much for the diagram, its a great help just what i needed and posted here for the benefit of others. Quote Link to comment Share on other sites More sharing options...
ciderman Posted October 31, 2007 Share Posted October 31, 2007 James , you wont get any continuity across the terminals until the relay is triggered . Quote Link to comment Share on other sites More sharing options...
Steve 90 Posted October 31, 2007 Share Posted October 31, 2007 James, Are there any numbers next to the terminals or a small diagram of the terminals with numbers on the casing somewhere? If there are give me a ring in the morning and I'll tell you where each one goes and what it does. Quote Link to comment Share on other sites More sharing options...
JST Posted October 31, 2007 Author Share Posted October 31, 2007 Steve - from the diagram ^^ think i can sort it but may ring anyway (although prob not tomorrow) from the diagram any ideas as to why there is a feed from the oil pressure switch? I got it as: 2 - earth 4- +ve ign 5 - switch (to earth) 6. oil pressure switch? - only come on with running engine? 8.. to relay to trigger the screen power which in turn is fed through a fuse. My screen only has 2 wires i think - for the one above 2 inputs and and earth it says 25A, so for one input? ideas on fuse size. Thanks for the help guys. Quote Link to comment Share on other sites More sharing options...
western Posted October 31, 2007 Share Posted October 31, 2007 James -- have you got the PRC7303 relay as well, otherwise known as a Hella 12V 4RA 003 510-46 embossed in the top face of mine, when I get round to fitting the wiring. Quote Link to comment Share on other sites More sharing options...
Guest diesel_jim Posted November 1, 2007 Share Posted November 1, 2007 from the diagram any ideas as to why there is a feed from the oil pressure switch? So that the front screen will only come on when the engine is running (to save the battery power). i suspect that if you left this connection "off" (un connected to anything) then the unit would work properly... if you put 12v into this connection (as if the engine was not running and the oil light was on, thus giving 12v) then it would "lock out" Quote Link to comment Share on other sites More sharing options...
David Sparkes Posted November 1, 2007 Share Posted November 1, 2007 Diesel Jim - Oil Pressure switch. My view of the diagram is that the terminal, and therefore White/Brown wire, on the oil pressure switch is at full Earth when the engine is not running, not 12v as your reply indicates. When the engine is running, and the oil pressure switch operates, the wire has a high resistance 12volt condition, coming from behind the warning light. Thus I would NEVER put full +ve 12 volts on the OP timer contact. I agree, the purpose of the OP connection is to prevent the heated screen operating until the engine is running (and the alternator can supply the electrical load). Disabling this function, by leaving the OP terminal unconnected would NOT enable the timer to 'work properly', as an important safety feature is missing. Yes, the screen would probably heat, but that is not a full definition of 'working properly'. Why omit the safety feature and leave JST with a trap to fall into? For the sake of one connection, why not do the job correctly? JST - Screen Connections. I'd double check whether you have 2 or 4 connections. Typically, modern screens are so powerful that they are split in two halves, switched and fused seperately. I don't know if you are looking at the actual screen, or some preinstalled wiring, but on the screen, two connections may appear close together, centre lower or centre upper edge, with two single connections at the outside corners, again either upper or lower. If your screen really does only have two connections then I'd put the relay outputs in parallel, but by all means just use one of those shown in the diagram. This is because, by definition, if only two screen connections exist, the screen isn't powerful enough to require two - see my fusing comments. For fusing you should contact the screen supplier, but I strongly suspect you do not have wiring in the car to take 50 amps to the windscreen, irrespective of the fuse, so I'd stick to a single 25 or 30 amp fuse. (My 38A uses two 30 amp fuses) HTH Quote Link to comment Share on other sites More sharing options...
Guest diesel_jim Posted November 1, 2007 Share Posted November 1, 2007 Diesel Jim - Oil Pressure switch.My view of the diagram is that the terminal, and therefore White/Brown wire, on the oil pressure switch is at full Earth when the engine is not running, not 12v as your reply indicates. When the engine is running, and the oil pressure switch operates, the wire has a high resistance 12volt condition, coming from behind the warning light. Thus I would NEVER put full +ve 12 volts on the OP timer contact. I agree, the purpose of the OP connection is to prevent the heated screen operating until the engine is running (and the alternator can supply the electrical load). Disabling this function, by leaving the OP terminal unconnected would NOT enable the timer to 'work properly', as an important safety feature is missing. Yes, the screen would probably heat, but that is not a full definition of 'working properly'. Why omit the safety feature and leave JST with a trap to fall into? For the sake of one connection, why not do the job correctly? I wasn't suggesting that anyone leave anything disconnected, was just stating what migh/would happen (As it happens i got it back to front! ) but i wasn't instructing James to connect it in any fashion Quote Link to comment Share on other sites More sharing options...
JST Posted November 1, 2007 Author Share Posted November 1, 2007 Cheers guys for the replies, fantastic help, screen goes in tomorrow so i will check connections then. ref the oil pressure feed dues it will be as 12v feed from the said wire then! Ralph - i was just going to use the timer to switch a normal relay to give a feed from the battery - that would work wouldnt it? Quote Link to comment Share on other sites More sharing options...
western Posted November 1, 2007 Share Posted November 1, 2007 Should do provided it can handle the current flow, the relay above ---- Hella unit is listed as able to handle 70amps but the fuse in my loom for the heated screen is 30amp. Quote Link to comment Share on other sites More sharing options...
Porny Posted November 1, 2007 Share Posted November 1, 2007 HEATED FRONT SCREEN - Post 2002 spec Td5 (as per JST) Item Description 1. Heated front screen RH connector 2. Heated front screen LH connector 3. Heated front screen ECU (behind instrument pack) 4. Heated front screen relay (passenger compartment fuse box) 5. Heated front screen switch The HFS comprises two elements laminated in the windscreen. The elements are connected by bus bars within the screen and therefore the HFS has only one feed and one earth connector. The HFS is controlled by the HFS ECU which determines when HFS operation is permitted. The ECU also has a timer which allows HFS operation for up to 8 minutes. The HFS ECU is located behind the instrument pack, adjacent to the dim/dip relay. The ECU is connected by a multiplug. The ECU receives an ignition feed via the satellite fuse box and an engine running signal from the engine oil pressure switch. A non-latching switch for HFS operation is located in the fascia. The switch has a tell-tale lamp to indicate when the HFS screen is operative. The HFS relay is located in the under seat fuse box and receives a permanent battery voltage supply via fusible link 1 in the under seat fuse box. The relay coil is connected to the HFS ECU and an earth point. When the relay is operated, battery voltage is supplied from the relay, via fuse 25 in the passenger compartment fuse box to the HFS element. When the HFS switch is depressed, a momentary earth path is completed from the HFS ECU, through the switch to earth. This is sensed by the ECU as a request for HFS operation. If the ECU receives an ignition on signal and an oil pressure signal, it allows HFS operation. The ECU provides an output to the coil of the HFS relay. When the coil is energised, the contacts close and battery voltage, via fusible link 1 in the under seat fuse box is supplied to the HFS element, via fuse 25 in the passenger compartment fuse box. The feed is also supplied via a splice joint to the HFS switch to illuminate the tell tale lamp in the switch. The HFS ECU will allow screen operation for up to 8 minutes, after which it removes the feed to the HFS relay coil, which, after the contacts open, removes the supply to the HFS element and simultaneously extinguishing the tell tale lamp in the switch. If, during the timed operation period, the HFS ECU receives an additional request signal from operation of the switch, HFS operation is stopped. When operating, the HFS element draws approximately 25 Amps. To prevent excess drain on the vehicle battery, if the ignition on signal and/or the oil pressure switch (engine running) signal is lost, the HFS ECU de-energises, if already operating, or will not energise the HFS relay. Ian Quote Link to comment Share on other sites More sharing options...
Guest diesel_jim Posted November 2, 2007 Share Posted November 2, 2007 Ian, does that mean that all post 2002 Td5's have the wiring in place for the screen? (as in, that bulkhead i got from you?) or was it a factory fit option only? (i've not looked at mine yet to see whats there) Quote Link to comment Share on other sites More sharing options...
JST Posted November 2, 2007 Author Share Posted November 2, 2007 Ideal thanks Ian, will be looking at it today sounds reasonable enough to put together. Will see how it goes today! Quote Link to comment Share on other sites More sharing options...
JST Posted November 3, 2007 Author Share Posted November 3, 2007 Yipee, its done, finished it this am, it all now works off the HRW switch, with consecutive pushes of the HRW button giving: HRW on FHW off HRW off FHW on HRW on FHW on All off FHW is on an 8min timer and must have the engine running for it to work plus uses the TC light to tell you its on!!!! Thank you for all your input and help guys. Quote Link to comment Share on other sites More sharing options...
Guest diesel_jim Posted November 3, 2007 Share Posted November 3, 2007 Great stuff James!! was it more or less "plug and play" or did you have to make up any looms? time to write a tech report for us thickies!! Quote Link to comment Share on other sites More sharing options...
JST Posted November 3, 2007 Author Share Posted November 3, 2007 Jamie, if i knew how i had done it and therefore how it worked i would do a tech article but alas i dont know but it works so i wont be touching it. i made up my own loom to patch in the timer and 3 relays in the end (1 for the HFS, and 2 to change output signals from +ve to -ve (1 for TC light and one from the HRW switch to make the timer switch come on)) Quote Link to comment Share on other sites More sharing options...
Peter Puma Posted February 6, 2011 Share Posted February 6, 2011 Hi guys, Most useful thread this one I've just finished installing the HFS electrics in my 2005MY 110. Although people told me that the wiring loom would already be fitted this proved not to be the case. So I put all wiring in myself , including the timer relay PRC6796. The 12V feed is taken from an electronics split charge relay that goes in only when the battery voltage is above 12.8V for > 1 minute. So I didn't use the OP wire that prevents the HFS from working when the engine isn't running. At the same time I'm also installing the DefenderVent kit (perhaps overkill in combination with the HFS). Honestly speaking I'm not too impressed with the quality of this kit, especially considering the cost of it. What is really below standards is the plastic flex tubing intended to connect the site vents to the main vents. This tubing is just too small to fit properly. Instead i found that the air inlet tubing supplied by Webasto is a much better option (although a bit too large but that is easily fixed). I'll post some pictures once all is ready . Quote Link to comment Share on other sites More sharing options...
JST Posted February 9, 2011 Author Share Posted February 9, 2011 Does anyone know where the HFS and HRW relays are located on a 11MY Puma 110? Quote Link to comment Share on other sites More sharing options...
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