1ezy

First thanks for this wonderful forum.

I have a 92 F150 4.9L I just replaced alternator and battery and nothing.

Checked all cables in and around battery and alternator and everything looks good.

It starts when jumped and the gauge is bouncy. When I turn on lights the engine revs up. If I turn engine off, nothing complete dead.

It died while leaving this morning and had to jump start to get back in the driveway.

Thanks for any help.

Mike

P.S. New Engine less than 1,000 Miles new plugs,wires, distributor cap etc..

LoneWolfTrucker

I'd have the new alternator checked. Sometimes they are DOA and that behavior definitely sounds like an alternator.

Also, make sure the to remove any corrosion from the alternator mounting points. Alternators are grounded and if it isn't properly grounded it won't function properly.

1ezy

I removed alternator. I'm on my way to get it checked.

Now I have another question.

I checked the voltage between my negative side of the battery and a spot on the truck and the voltmeter goes in reverse.

This doesn't seem right.

Could I have a short somewhere? (Ignition Switch)

Should the lights and radio etc still work if battery is fully charged? (without alternator)

Thanks

Mike

dewman

Your accessories should run with/without the alternator, I believe. They run off a feed from the battery, not the alternator. My understanding is everything runs off the battery and the alternator's function is to keep the battery charged. I could be wrong though and I am sure someone will correct me if I am.

wde3477

By 'a spot on the truck', I am assuming you are meaning another point which should be grounded.

If so, speculating that you have a high resistance path to ground - in other words, poor grounding somewhere. The voltage between a grounded point and the battery should be doggone close to zero.

Accessories may not be particularly sensitive to a 'good' ground - they just need a sufficient voltage difference between the supply and ground leads.

A 'bouncy' voltmeter gauge is not a good thing - something is not right. If the alternator checks good, perhaps consider a load test of the new battery. Maybe do resistance checks with the battery disconnected - for what the multi-meter can provide in the way of source current, the large ground lead(s) should appear pretty much as a direct short. All connections have to be clean and tight.

thejon2524

make sure the alt is grounded properly