Lotus Elan

Fried Ammeter?

PostPost by: archigator » Sun Jun 18, 2006 1:09 am

I'm not an electrical genius, but I'm trying to work my way through some gremlins in my 12-volt negative ground ignition system. Returning from a ride in my '71 Sprint a few weeks ago, smoke started wisping out of the dash where the radio is located (if I had one.) The wires in the dash harness were hot to the touch, and when I went to restart it after it cooled... I got nothing. Not even a click. I opened the hood (bonnet) to find my original fuse box partially melted! The two 15 amp fuses, however, had not blown. (Is 15 amp the correct fuse for the original Lucas fuse box?)

I know I have a good coil, ignition switch and starter solenoid (all new). I have determined that I have voltage from the battery to the solenoid and from there to the dash ammeter, but when I put the volt tester (light) to the opposite side of the dash ammeter (leading to the ignition switch) I get no reading. Can I make the logical assumption that my dash ammeter is toast? (It's a 50 amp Smiths) Should I bridge the gap across the ammeter to see if I get a completed circuit to the ignition switch? and what could have caused this to happen all of a sudden, a wire that accidently grounded itself where it shouldn't have? Thanks for your help.

Gary
'71 Elan Sprint RHD
Miami, FL

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PostPost by: types26/36 » Sun Jun 18, 2006 10:43 am

archigator wrote:
I have determined that I have voltage from the battery to the solenoid and from there to the dash ammeter, but when I put the volt tester (light) to the opposite side of the dash ammeter (leading to the ignition switch) I get no reading. Can I make the logical assumption that my dash ammeter is toast? (It's a 50 amp Smiths) Should I bridge the gap across the ammeter to see if I get a completed circuit to the ignition switch? .
Gary


Gary,
I'm probably reading your post wrongly but when you say " when I put the volt tester (light) to the opposite side of the dash ammeter (leading to the ignition switch) I get no reading" you are going from terminal to ground and not from terminal to terminal as term to term would show nothing.
I would suggest you buy a volt/ohm meter, they are not expensive and while a test light is O.K. it only shows if power is there and not the actual voltage. As well as being able to test for voltage you can check accross the ammeter with the ohm meter for continuity (one term is connected to the other)
I dont know what has happened to your car but my first thoughts would be to check all the earths (grounds) as a bad connection can cause all sorts of problems, once the car is running again have the generator or alternator output checked.
Brian
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PostPost by: archigator » Sun Jun 18, 2006 11:36 am

Brian,

The Lucas Diagnostic Manual shows ((if I'm reading it right) power in to the ammeter (thick brown wire) from the solenoid, and power out from the ammeter (another thick brown wire) at the oppposite terminal of the ammeter. Shouldn't both brown wires be hot always, with the power just passing through the ammeter from one side and out the other? (However when the car was operating properly, I remember the ammeter dial not reading anything but zero until the ignition switch was turned in the ON position.) There is a much smaller black ground wire (a red wire in this photo, since corrected to black) that goes directly to the nearby chasis ground.

I've put the voltmeter on each ammeter terminal individually, and then to ground. I get a reading on the input side, but not the output side.)
Thanks again.

Gary
'71 Elan Sprint RHD
Miami, FL
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Back of Ammeter
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PostPost by: types26/36 » Sun Jun 18, 2006 2:55 pm

That is correct, the brown wire is permanently hot (live) but the ammeter will not show a discharge (or charge) untill a current consumer is switched on and the power goes through the ammeter (and through the consumer )to ground.
I would think you have a light in the ammeter so you are likely to have a red (power from light switch) and a black (ground) for the light.
It sounds like you are doing the test (each side of ammeter to ground) correctly, if you are getting a reading on input side and nothing on the other side,I would agree that the ammeter is probably burnt out.
Try bypassing the ammeter and see if you get ignition feed.
I would still check the earths (grounds) for the engine/gearbox and battery where it goes to ground at the rear.
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PostPost by: archigator » Sun Jun 18, 2006 4:07 pm

Thanks Brian. Your help is much appreciated. (It's pretty amazing getting advice from a fellow Sprint owner on the other side of the planet. Great Forum.) When I find the problem's source, I'll post it here.

Gary
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Miami, FL
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