87 T TOP GT302

I got a problem with my 87 Mustang Battery gauge. I had a new ,Motor Craft, battery installed about 2 years ago. Also a new alternator ,bought from summit racing last summer. The reason I bought the alternator from summit was I wanted one the is polished. I'm not sure of the amp.
My vehicle is not driven a lot but I've charged it up 3 times in the past 2 months. Also I bought a battery tender recently so that stays on it all time unless its running.
My concern is the battery gauge reads low all the time. what could I be missing?

jwog666

first thing, you need to check the battery voltage with a volt meter with the engine running, it should be around 14v, if it is then i would suspect the battery gauge is inaccurate

88 orangepeel notch

+1 ^^^

And I'd also yank those underdrive pulleys off if your running a stock 75 amp alternator.

87 T TOP GT302

I checked the voltage to battery and when car is cold it reads 12.65. After it gets warmed up it drops to 11.90.
I know I said I wasn't sure on amps on alternator but I know it's over 100. I'm just not sure how much over 100 it is.

jwog666

your alternator is not charging, it has nothing to do with amps at this point, this is why the gauge is reading low

87 T TOP GT302

For some reason the gauge is now showing to be charging. Sets just above 1/2 at idle. Idle is at 900 rpm's.
Recently I've been adjusting idling and resetting it. While it's was idling I noticed the gauge was actually past halfway. Not sure why but its good now.

67LimeCoupe

The stock gauge is crap, as was mentioned above, you shouldnt be running UDPs with a stock alternator. The alternator wont spin fast enough to charge the battery properly. If the battery isnt at 14+ volts at idle the problem isnt fixed.

mjr46

what type of alt is it?? stock polished replacement? 1 wire self exciting?? 3g upgrade??

Jfsram

It may not be up to the standards of a factory vehicle but a little discharge during idle will not hurt anything.

88 orangepeel notch

True, it won't actually hurt anything. I drove my car this way for years. But on a cold, rainy night with the headlights, wipers, and blower on low, the headlights were so dim they were useless, wipers barely moving, and my feet got cold from the blower not moving any heat lol.

Just an example, but swapping to a 3G was literally night and day difference. Wish I'd done it sooner.