AJAS Posted March 18 Report Share Posted March 18 Hi all I’ll give you the problem before the background so if you’re not interested in the topic you won’t waste your time! Last drove my 69 TR PI a week before Christmas when I took it for mot. Since then I swapped to an overdrive gearbox. Switching on ign to test overdrive electrical function there is no ign light (but have oil pressure light) and I find I have continuity between the battery +ve cable and earth, when the cable is either connected to the battery or not. Also appear to have continuity between +ve and -ve battery terminals. Am I being a numpty and missed something? More detail. As above it drove fine for it’s MOT. Since then I have swapped to an o/drive gearbox, plus a new gearbox-to-body wiring loom and overdrive relay. Checked the function of the overdrive switch and the isolator switches and had continuity in all the right places. I then hooked up the battery (fully charged) switched on the ign and had no warning light. Reverse lights work. No switching from the relay. Checked the ign bulb and it has continuity Checked the ign light feed at the alternator and replaced the small connector – I noted that there is a loose earth wire from the alternator body, but reading up in the forums this is not needed as the alternator is the 3 terminal jobbie, with 2 individual connectors (1 large and 1 small). There is a snipped thin brown wire in loom near the alternator which is also part of the conversion I believe. I’ve checked the starter connections and replaced the ign connector. I have disconnected every wire in the overdrive circuit one by one and checked continuity at the +ve cable but no change. Any thoughts / suggestions and prompts gratefully received Quote Link to post Share on other sites
RobH Posted March 18 Report Share Posted March 18 (edited) It isn't exactly clear to me what you are doing with these 'continuity' tests nor why you are doing them. Depending on what you are using to do the measurement you may get all sorts of weird results, because everything is connected to everything else in some way and an over- sensitive meter can show connection where the path is rather tenuous. The best instrument for electrical fault-finding on a car is a small 12v bulb with wires attached. You say there is 'no switching from the relay' - what relay is that? Do you mean the starter solenoid? It's also not clear what type of alternator you have - 'three-terminal jobbie' could be anything. Is it a Lucas or a Denso type? If you are not sure a photo would help. Did you try anything other than reversing lights? Do the horns, indicators or headlights work ? Edited March 18 by RobH Quote Link to post Share on other sites
AJAS Posted March 18 Author Report Share Posted March 18 Thanks for getting back to me. Firstly, I am more of a mechanical person than electrickery. Answers to your questions: I am simply using a multi-meter set to 'ohms' and placing a probe against a connector and the other to earth. The reason I started doing the test was two fold - one to ascertain whether the switches on the overdrive were working and secondly I have an earth disconnect coupling on the -ve battery cable and was just looking to see how sensitive it was to unscrewing the coupling. At that point I found that the -ve terminal and the supposedly disconnected cable was still showing continuity. Following around, I then discovered that the +ve battery cable, when disconnected from the battery showed continuity when one probe was on the connector and the other on an earth point. As the car was put away with no electrical fault and I now appear to have no ign light working and the +ve cable seemingly having continuity to earth I assumed that both problems are related. The starter motor was the only thing moved that has electrical connection so I assumed that would be the cause of the problem The relay referred to is the 6RA type for the overdrive solenoid. There are no manufacturers name on the alternator. Pictures attached - there is an etched code on the top of the alternator - AS D18, which brings nothing up on a quick search, nor the code from the sticker Didn't try anything else as I have only disturbed wiring relating to the switches on the gearbox Quote Link to post Share on other sites
BlueTR3A-5EKT Posted March 18 Report Share Posted March 18 The alternator looks like a Lucas ACR type. As Rob has said use a bulb and wire for simple continuity test. The ohmmeter is probably too sensitive Get one of these https://www.ebay.co.uk/itm/256441484251?_trkparms=amclksrc%3DITM%26aid%3D1110018%26algo%3DHOMESPLICE.COMPLISTINGS%26ao%3D1%26asc%3D260662%26meid%3D84c8720c0db54f43ad0164c32a06c2ee%26pid%3D101196%26rk%3D2%26rkt%3D12%26sd%3D192846063407%26itm%3D256441484251%26pmt%3D1%26noa%3D0%26pg%3D4429486%26algv%3DCompVIDesktopATF2V4WithDefaultIMAFeature&_trksid=p4429486.c101196.m2219&itmprp=cksum%3A25644148425184c8720c0db54f43ad0164c32a06c2ee|enc%3AAQAJAAABALUK373GZYwoSkhvUXwZwr2SLMQzpCH9tKsUlXR5IUOVFg6%2BDk7Rw1OZXS%2Bb4%2BWbabZIsOOgx9SJlBDGdIYZhZExEbg0jEfdTcG84O%2FdDMKTYv7VS2x1aQjNZyhAUvr7XqTMjIgQg1xequ%2Bu%2BrxIZZTxSwji39Ft%2FFn3Plt9aXhrHqZpLZ%2B6fdqphdeSBjacSnBHoChXisF4Q9uis2%2FUdjus%2FRoVJyA41PHXBMPofeiXrUojUmcHqds4t4nNYkRQ%2BOGumS4LNglOtIYlGlOYKsZZos10LnHz1rGFpngEOyoi1lvTOqzbCAorW%2FTtxjTPS6aPgpN4qnTn8OKb3qssvdk%3D|ampid%3APL_CLK|clp%3A4429486&epid=1159836048&itmmeta=01HS9BH5FT3RF9YSG0005DXA5X Quote Link to post Share on other sites
RobH Posted March 18 Report Share Posted March 18 (edited) Ah - OK. That is a Lucas ACR pattern alternator. The continuity tests you are doing are finding return paths through equipment in the car which is why it looks as though the positive lead goes to earth. It is not a meaningful reading. You say the reversing light works - which is an indication that the battery is OK but more than that depends on where it is connected and whether it is switched by the ignition switch. The fact the oil light comes on with the ignition shows there is power to the switch and that the switch is working. It should also feed power to the ignition light, which earths via the alternator, and also to the indicators so they should work too. If they do we need to look at the alternator end of things. There is a thin wire connected to the alternator - probably the one on the right in your photo. It ought to be brown/yellow but since alterations have been made to your car that may no longer be the case. That wire is the other end of the ignition lamp and if you disconnect it from the alternator and connect it to earth, the lamp should come on when you switch the ignition. That would prove that part of the circuit is ok. Are you sure the engine is properly earthed to the chassis by a heavy braid ? Edited March 18 by RobH Quote Link to post Share on other sites
keith1948 Posted March 18 Report Share Posted March 18 Take relay off car. Put power across W1 and W2 and you should hear the relay click on and off if it is working. You could just put the meter across C1 and C2 to check that power across W1 and W2 switches C1 to C2. If you tell us what numbers and letters are stamped on the relay then we can identify what you have. If it works on the bench then refit to car and check wiring. Your relay should be the 'normally open' type. 6RA is simply a generic number for a range of relays. The numbers starting 33 or SRB identify which is which. Keith Quote Link to post Share on other sites
AJAS Posted March 19 Author Report Share Posted March 19 Thanks both for the pointers you've provided. I'll crack on with your suggestions after a second brekkie cuppa! Quote Link to post Share on other sites
AJAS Posted March 19 Author Report Share Posted March 19 Hi again. An update. Just to re-iterate, the car drove fine with the ign light operating as expected before I did the gearbox swap. Alternator conversion undertaken before my ownership Checks made today Swapped oil pressure warning bulb to ign warning location, still no light when ign switch on Indicators and all lights work when ign key on – note this is a new ign switch (3 months old) Earth strap from body to engine to battery -ve terminal in place 12v at ign switch from starter motor wire (red / white wire) when ign switched on Alternator 1 Large wire connected – brown / white trace 1 small wire connected – brown (not much visible so could be brown / red?) spliced to an extended wire and connector, live with ign switched off or on! Snipped wire – brown / yellow trace, switched from 0v to 12v when ign switch turned on which according to the diagrams is the ign light Relay New (2 weeks), bought from Moss, I think Numbers 542-170, 142169A Wiring W2 – yellow / green C2 – yellow / purple W1 – white C1 – black When 12 v applied across W1-W2, relay clicked and C1-C2 connected Looks like the alternator wiring is wrong? Quote Link to post Share on other sites
RobH Posted March 19 Report Share Posted March 19 (edited) 2 hours ago, AJAS said: 1 small wire connected – brown (not much visible so could be brown / red?) spliced to an extended wire and connector, live with ign switched off or on! Did you measure that with the wire disconnected from the alternator? I'm getting a bit doubtful about all this as there is a chance for something to go very wrong and cause damage or even a fire unless you are careful as there is no fuse in the battery connection to the alternator. If what you say is correct and the ignition lamp really was working before, then whoever installed the alternator must have fiddled with the wiring in a non-standard way so the colours on the small connection are not right. If that thin wire is really live all the time it may be part of the original wiring as the old alternators did have a live feed from a four-way junction point (which I think is on the wing) but why was the wire cut and then extended? Did he cut both wires by mistake and then maybe extend the wrong one? If so the ignition light could not have worked afterwards. You say the ignition switch has been replaced recently - did you do that yourself? Were the wire colours on the switch as per the diagrams? Does the bulb-holder for the ignition lamp have one white wire and one brown/yellow one? If so does the brown/yellow wire go to the 'snipped' wire or to the extended one? Edited March 19 by RobH Quote Link to post Share on other sites
AJAS Posted March 19 Author Report Share Posted March 19 Thanks for getting back to me. I'm pretty sure I tried with the wire connected and disconnected, but I'm starting to doubt myself!! I replaced the ignition switch myself just swapping wires over from the old to the new. I can't get back to check until Thursday now, so will have to wait. Battery is disconnected Thanks agin Quote Link to post Share on other sites
AJAS Posted March 19 Author Report Share Posted March 19 To save my sanity, I nipped out and checked while my dinner is cooking. Definitely live with the ignition switch off and wire disconnected. Btw, I am reasonably competent around wiring, but this had me stumped when comparing with the wiring diagram. Like you, I'm pretty sure the wrong wire has been used, so will try the one that appears to be switched by the ignition Before I swapped the ignition switch I checked the wires with the wiring diagram and all was as expected Quote Link to post Share on other sites
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