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Post by p5andrew on Mar 4, 2022 22:59:45 GMT
I have made and fitted a secondary fuse panel which incorporates relays for headlamps, electric fan, electric fuel pump and ignition system. I have also installed an inertia switch wired to shut off the fuel pump and ignition in the event of an accident. I am now at the stage of connecting the feed to the panel. I plan to take the panel feed from the ammeter in order that the ammeter correctly registers the load from the new panel. However, on preparing to connect up to the ammeter I find that it’s cables are a good deal smaller in section than I expected given the load involved. This leads me to wonder if there is a shunt buried somewhere behind the dash, although nothing is shown on the wsm wiring diagram. Is there in fact a shunt? If not, I shall go ahead as planned. My car is a 1971 P5B coupe.
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Post by djm16 on Mar 5, 2022 2:11:33 GMT
There is no shunt. The cables are quite heavy in comparison to modern car wiring, but if you are concerned, then turn on all the electrics and feels for a temperature rise in the wire.
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Post by Phil Nottingham on Mar 5, 2022 6:44:16 GMT
P5Bs do have a shunt
It is right at the back on the parcel shelf rail under the instrument panel. Its near the massive heavy duty Lucar busbars and difficult to reach and see - follow the heavy Brown/White and Brown cables. You need the Brown/White cables to register correctly.
Do not connect anything to the ammeter terminals. The best place to take a live feed from is the ignition switch which is fed from said Busbars/Br/Wh cable
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Post by p5andrew on Mar 5, 2022 17:17:51 GMT
Many thanks for the responses.
I thought there had to be a shunt somewhere, the cables to the ammeter being much too small in section to carry heavy current. The feed to the secondary fuse board needs to be permanently live in order that the headlamps will work with the ignition off. It seems to me that ideally I should take my feed from the busbar which Phil mentions. The only challenge is that it is well-buried and not particularly accessible, especially for someone of my "generous" proportions! However, there is always a way...
I should perhaps mention that the feed to the inertia switch is taken from the ignition control fuse on the original fuse board, this feeding the relay coils for the fuel pump, ignition and electric fan, so these circuits will only work when the ignition is switched on.
Andrew
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Post by Phil Nottingham on Mar 5, 2022 21:35:56 GMT
Take from the Ignition switch Main Feed Brown/White - its easier!
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