a little help electrical problem

i rescued a 1972 monte carlo out of a garage this weekend. we got the car running and driving the car starts with no problem and runs fine.

after we did this we decided to try everything else and nothing works, headlights, brakelights, turn signals, heater nothing electrical. so we started to check things, there is no signs at all that a animal has made a home in this car so chewed wires are not a option. the thing we did find is the frame of the car is postive charged it is not grounded.

so that is telling me there is a direct short somewhere but no smoking burning wires. the car will sit there and run all day long.

what would be the best way to find the short ....most of the time its follow the smoke but no smoke this time

Sounds like a bad chassis/body ground. It's trying to find a ground through the test light, making it light up.

later, matt

Not knowing anything specific about ~40 year-old GMs, I'll throw a couple random ideas out.

If both + and - battery leads connect directly from the battery to the engine/starter/alt, but there was no frame ground from the engine, you could possibly have a closed circuit for the engine to run, but with no chassis/frame ground everything else would read +. However, if the car starts with the key, that would mean the ignition is also wired directly to the engine without using a chassis/frame ground, which would surprise me.

petegossett wrote: However, if the car starts with the key, that would mean the ignition is also wired directly to the engine without using a chassis/frame ground, which would surprise me.

that is what is throwing us off. we ran a ground wire from the batt directly to the frame and it started to get hot and we pulled it............as my nephew said we are so use to trouble shooting BMW's with multiple computers and things that we do not know how to handle something so basic

Old GM ignition switches are only grounded for the bulb check. Other than that they switch on the positive.

later, matt

first, don't be misled about the chassis being +. the temperature of the ground wire you made is directly proportional to the amount of amperage flowing through it and inversely proportional to the gauge of the wire. ie wire too small for load gets hot. basically, you'd get a spark show and much melting if you had both B+ and B- connected to the chassis.

wiring is very simple on these cars. i'm working from memories going back to 1992, but this should be just about 100% right.

Battery B-: there is one black cable that goes to the alternator bracket (or other suitable engine ground). somewhere else (don't remember exactly) there's probably a ground strap from the engine to the chassis.

Battery B+: There should be two wires going to B+ on the battery.the big-ass one that goes to big lug on starter, and a 10-ga wire that comes from the B terminal on the alt.

At the big lug on the Starter, you should find two or maybe three wires: for sure the big-ass B+ cable, and for sure a 10-ga that goes to a power distribution point somewhere (iirc it goes to the horn relay which is probably mounted on the driver's side inner fender or on the firewall, but it might just go to a stud somewhere that will (should) have other wires with ring terminals attached to it).

Here's where my memory is slightly fuzzy. i think there's a third wire from the big lug on the starter that goes to the ignition switch in the column, but it's possible that this wire could go from the power distribution point to the ignition switch, rather than going directly from the starter.

so, if the car cranks with the key, you know that you have power to the starter, you have power from the starter to the ignition switch, and you have power from the ignition switch back down to the "S" terminal on the starter.

on top of that, if the engine actually starts and runs with the key, you know that you have +12v to the ignition coil when key is in "start" and you have at least +9v to the ignition coil (via "resistance wire") when key is in "run".

so, it sounds like your problem is either:
- the wire from the big lug on the starter to the power distribution point is kaput (this may be a fusible link),

OR

• there are no other loads connected to that power distribution point.

i do not recall if the other wires coming off the power distribution point would be through fusible links or not.

Continuity check ?

Just got word from nephew it was the body ground strap. Cleaned the grounds and added one. Everything works now. I may have to raise price on car now