240: idiot lights inop after battery swap

[esmth]

Hello all,
The other day I swapped my group 47 AGM battery for a mini pc680 battery. I also replaced all of the high current battery wires and grounds. First time I go to start the car with new battery, the idiot lights all shine in key position 2 as normal. Engine cranks and starts normal. A couple minutes later I re-start the car and none of the idiot lights light up in key position 2. (except the service and check engine) The speedo is also jumpy when cranking the car. Car starts just the same though.

The alternator is definitely charging. 100 amp denso recently refreshed. does not need a rev to self-excite. I get 12 volts at the exciter wire in key position 2, and grounding this to the block allows the lights to shine as they should.

Right now i'm about to clean up the low current engine grounds and verify all the new alt/starter/ground wires I installed the other day.

Anything else I should check to try to get the dash lights to work as expected? Thanks!!

[dl242gt]

It is probably time to check or replace some fuses. The ground on the alternator can also cause the excitor circuit to not function so I think you are on the right path.

[cleanflametrap]

Originally Posted by esmth

... I get 12 volts at the exciter wire in key position 2, and grounding this to the block allows the lights to shine as they should. ...

How are you reading the 12V at the exciter wire? Are you pulling it off of the alternator and sticking your meter probe in the end of it? Or are you measuring it in-circuit, backprobing the connector?

I suspect the former. If grounding it gives you the lights back, and with it reconnected, the warning lights fail lamp test but remain out when the alternator is charging, you have a problem at the alternator. The ground wire seems a likely suspect as Dave mentions.

Backprobing the exciter wire should yield about a volt and a half key on engine stalled, and 13.6 or more with engine running.