Who's good at electrics?

[Baldrick56]

My new (to me) 300E has been under suspicion from the word go as the battery went flat after a weeks inaction. However battery was a dud so bought another but that one did seem to deplete steadily if left for a few days. For that reason I've been in the habit of disconnecting the earth lead whilst its not being used. Its been "not used" a long time now because I've been doing bodywork repairs, today however was time to move it out of the workshop. As I went to reconnect the battery there was a massive spark & almost a 'hum' of current. Quickly detached lead & got the multimeter, there was 9 ohms between pos. pole & an earth on the car. Now my immediate reaction was that it must be something I'd disturbed in the course of the other repairs. I was doing welding in the vicinity of where cables run & I'd 'slewed' these out the way of the searing heat (hopefully). I spent about an hour removing fuses one by one & retesting - same result, 9 ohms. The 'short' therefore had to be 'upstream' of the fusebox (or in an unfused circuit). There were some 'additional' wires snaking away from the pos pole - removed these - no difference. I traced the pos. cable & found one branch went to a junction box with a hinged plastic cover (mounted close to the shock absorber top mount). This had three other cables going "somewhere" held by two 10mm head bolts - tested each of these in turn - 'infinity,' 'infinity,' & 9 ohms. Reassembled without the offending cable, reconnected battery, & to my utter amazement car started & ran just fine - so it's obviously not a vital 'system' cable. Anyone know what it does? where it goes?

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Thanks,
Rob

[Henry Schuman]

That Junction Block I believe is where the Alt. ,Lights, and maybe seats or windows get there main voltage from so Something ain't gonna work now with one group disconnected . I THINK you will find the head lights or windows,A/C, Rear Window Defrost , or some other consumer not working now .
And are you sure you are measuring ohms and not AMPS or Voltage ???

[Baldrick56]

Thanks Henry,

yes I'm sure something must now be inoperative all I did was back it out the garage & manoevre clear of the door (cannot test it further than that for time being 'cos it's 'unregistered' for the road). Truth is that seats never worked from word go, windows neither (found the reason for the drivers window not working when I removed doorcard to find no motor or 'quadrant' & wooden stick propping up glass). Sunroof similarly not working, nor rear headrests. Lights did appear to work, ditto wiper (but not re-tested these since this problem). Have to say I was staggered at the amount of cabling when I pulled up the front carpet/floormoulding.

My goal is not do attempt a full "restoration" of this vehicle (ie with all it's original features) but rather to make a reliable 'daily driver.' To this end I've come by an almost complete replacement 'interior' but with (downmarket) manual adjustment seats so intending to remove all that particular electrickery. Similarly I've now given up with the sunroof (described elsewhere on this forum as a "diabolical mechanism") - if I can make the aircon. work that'll be good enough.

I'm thinking for a thirty year old car there's almost certainly been a degree of 'fiddling' with the electrics over the years - am wondering if I'm better off just getting one of the 'universal' wiring harnesses for a couple of hundred bucks & starting again with a 'simplified' system - dunno.
Regards,
Rob