Amp light on

[brsvo]

My amp light is on and it runs fine and has 13.9V across the battery after running in the driveway for 45 minuets! Should say my 86 has the 3G conversion and I checked the jumpers and none are out of place any ideas?

[grntRUDD13]

Mine does the same thing. It runs fine but it lights up occasionally, and isn't repeatable. No clue why. Am getting a code reader soon, hopefully that will enlighten me.

[MikeFleming]

The EEC has has nothing to do with the charging system in the SVO - so it won't help in that arena.

[Ford Builder]

Check your connections on the back the alternator and on the plug on the regulator may be green from corrosion.

[MikeFleming]

Sounds like a diode is going bad in the alternator. You can easily see a diode failure with an oscilloscope. Very difficult to detect any other way.

[blueboss]

Check the voltage across the battery with the engine running. If your regulator is bad or going bad, you can be overcharging your battery. 13.9v static is a little high IMHO. Should be around 12.75 to 13.5 v across the battery, engine off and 14.25 to 15v across the battery, engine running, accessories off and the regulator "cut in" rpm reached.

[brsvo]

The 13.9 was running at idle. My 3G is internally regulated I believe so if its putting out 13.9 it is still working correct? Also the 3G conversion has a large output wire (#4 believe) bypassing the green plug. What triggers the amp light?

[MikeFleming]

The 13.9 was running at idle. My 3G is internally regulated I believe so if its putting out 13.9 it is still working correct? Also the 3G conversion has a large output wire (#4 believe) bypassing the green plug. What triggers the amp light? Fully charged the battery voltage should be between 13.8 and 14.4 VDC (for normal lead-acid batteries).

However that does NOT mean all is right with the alternator charging system. Measuring DC voltage does not show the amount of ripple or AC noise. That needs to be measured with an oscilloscope.

A bad diode will put all kinds of electrical noise (frequency varies with RPM and load) through the electrical system with high and low spikes - this noise and spikes will not be detected by a DC voltmeter and the regulator will go by the average battery voltage and not by the noise or spikes.

If the light is flickering, 95% of the tiem there is a problem. Take the alternator to a local rebuilder and have them test it. Look specifically for a bad diode. The auto parts stored testing capability is very primitive, imho. I've never seen an auto parts store tester show a failing diode.

[grntRUDD13]

Well all this will give me a starting point. Shitty weather here (ice) so I'll have plenty of time to troubleshoot before I drive it.

[Meotchh]

A common problem with the 3g is the little white jumper wire not making a good connection which causes the amp light to flash on or stay on. The plastic plug becomes brittle & causes a poor connection. A new jumper will cost about $5. We picked up a handful in Sturgis to fix Dave Schmitt's blue beast. It had the same problem.

[brsvo]

Thanks for all the ideas, I won't have time to test the wire theory till spring as it was 0 overnight here. The motor is out of the car now for a bottom end refresh over winter.

[Meotchh]

You don't need the engine in the car or running to test the plug. Just use your eyes & maybe a multimeter. check for brittle, broken or melted plastic. Also check continuity off the wire from end to end.

[brsvo]

True and I could take the Alternator in and have it tested too. It snowed today so I have all winter to get it checked out.