Strange Elec issue

89 4.0 auto

So driving yesterday, voltage meter starts to drop. finally it end up in the red next to the 9

1. got out and pulled the neg cable from the bat and the engine died. (thinking its the alt). well, vehicle started right back up still reading 9volts. when i put on the gas the meter would raise about a volt.

2. headlights never dimmed, but the dash lights dimmed over time.

3. when i put on the turn signal the power to the radio cut out.

was able to drive it with the lights on 200 miles. so thinking alt is still good.

figure i have a loose cable somewhere. going to go over the complete assy from bat/alt all the way into cab. Anyone have an idea where to look for an issue liek this?

1. NEVER REMOVE A BATTERY CABLE WITH THE ENGINE RUNNING--unless you want to end up buying a lot of expensive electronic components. That stunt went out of style with points and condensers and carbs.

2. Remove the battery cables--this time with the engine OFF--clean the terminals and charge the battery overnight (Ok) or for 24 hours (best), and then have it load tested. While the battery is charging remove the primary cables completely from the vehicle. Clean both ends, and then check the cables with an ohm meter--resistance should be near ZERO; if not replace the cables. Good time to renew your grounds, the head to firewall braided strap is always a problem, replace it with a 4 ga cable.

Ok, battery fully charged, passed a load test, clean and tight cables, grounds renewed. Now, start the engine and check the voltage between the battery's terminals--should be about 13.6~14.5 volts, if not have the alternator tested.

If the bat was bad, wouldnt the headlights dim?

and why would the power to the radio cut out with a turn signal?

joe_peters said:

1. NEVER REMOVE A BATTERY CABLE WITH THE ENGINE RUNNING--unless you want to end up buying a lot of expensive electronic components. That stunt went out of style with points and condensers and carbs.

Click to expand...

Agreed. That is an "old trick" that dies hard. Don't do it.

Follow Joe's advice above; gotta get down to basics with electrical.

1. Load test battery. It is the ONLY conclusive way of determining battery condition.
2. Renew grounds; they are problematic with your vintage. Can't tell by looking at them.
3. Measure alternator output at the battery with a meter; you are looking for around 14.4 volts give or take a bit at high idle.

Apostle said:

If the bat was bad, wouldnt the headlights dim?

and why would the power to the radio cut out with a turn signal?

Click to expand...

Headlights are dimming, you just can't tell it.

Turn signal draws your 9V down to less than the radio needs to function. You are just lucky that the PCM/coil/etc. is still working down at 9V.

As suggested, connections (incl. grounds) are first, then check alternator, and if those steps fail, you need to go after voltage regulator. I see you have an 89.....good part is your regulaotr is built into the alternator (IIRC).

joe_peters said:

1. NEVER REMOVE A BATTERY CABLE WITH THE ENGINE RUNNING--unless you want to end up buying a lot of expensive electronic components. That stunt went out of style with points and condensers and carbs.

Click to expand...

Yup, watched it happen on a kart running a Ford EEC-IV controller. The dipstick had wired the mandatory kill switch in so it disconnected the battery, but the generator feed was on the wrong side of the switch. When he tested the kill switch the night before the race, he found out that engine computers aren't too happy seeing the 40-volt voltage spikes from the alternator.