Expert: jack bahm - 6/3/2009

Question
QUESTION: The lights (head, tail & brake) stopped working on my 30 model A.  In running diagnostics I find that the ignition & coil are wired in the junction block to the hot side, so the car runs OK.  The light are wired to the other junction block terminal after the ammeter.  The hot post in the light switch shows 6 1/2 volts but does not power the lights.  If I run a jumper from the hot starter post to the light post in the light switch they work OK.  If I jump the terminals on the junctions block together everythng works OK (but probably not the ammeter).  Any thoughts?

ANSWER: That's atough one, but it looks like you are getting to it.  The hot wire for the lights comes off of the generator, which runs up to the driver's side of the term box.  I'll send a wiring diagram if I can find it.  If you have a good 6 volts at the gen. then the light system should get enough power.  I would take a hard look at the ammeter.  It must have high resistance.  It probably gets hot when you try your lights normally.  My guess is the ammeter.
Good luck  If it continues to give you problems, get back to me and we will get it fixed.  I can't attach the diagram to this note.  If you need it, send me your e mail address.

jack

---------- FOLLOW-UP ----------

QUESTION: I also believe it is the ammeter.  I bought a new one and noticed when replacing the old one that the plastic cap on the connection lug was not there, probably separated due to heat. When inserting the new ammeter into the dash housing it registers negative 10 amps (I think its magnetic influence from the speedo)  I haven't installed it yet.  Should the ammeter show any resistance with an ohmmeter, and is it normal form the ammeter to be effected by magnetic influence? (I am thinking of using a small magnet on the dash housing to counteract the magnetic pull from the speedo).  thank for your help.

ANSWER: Forget the mag. bit.  I don't think that can happen unless somehow you got the needle charged up.  There should be no current draw that would pull the ammeter over.  It must spark when you connect it????
You may have a bad, new, ammeter.  Try to trace a short somewhere in it.  
Let me know what you find.
jack

---------- FOLLOW-UP ----------

QUESTION: Thanks again for your info.  How can I go about testing the ammeter to see if it is defective and/or if it is working properly?

Answer
Put an ohm meter across the terminals to ground,( the case).  There can't be anything there.  If something is touching, then find it and fix it.  Not too much to an ammeter.  I'll dig one out and play with it.  If I find some new info, I'll get back to you.
jack
I found an old ammeter, and the two term's must not be in any contact with the case.  It should be easy to fix, everything is right in front of you.  Take the ammeter completely out of the system and connect the two term's together.  If the car runs OK, then you are on the right track.  You don't need an ammeter to run the car.
jack
ps, I will be out of touch for the rest of the week.
jack