"92" AMP/Volt Gauge Dropping

[HardRock]

Ok..long story short...I put a new motor in my K1500..and now my amp gauge is funky. When you first start it up it reads 14..the warmer it gets the more it drops. I grounded the body good and the motor. I bought a new 160amp alt, ($200) and that did nothing. I do have underdrive pulleys on it but now have the factory pulley on the new alt. I took it to a GM dealer and they put a meter on it and said it was charging 13.69 with everything on but I still am not convinced. I ordered a new digital cyberdyne volt gauge today but not sure about that either. When I use the signal light if you watch very closely at the fuel and oil needles they bounce with the signal light. When I am driving if you turn the heater on or headlights the gauge drops instantly. I am pulling the hair out of my head..I really could use some input soon..this is my tow truck for my drag car and the races are coming soon! If anyone can help me I would greatly appreciate it. Oh ya battery checks out fine with the load tester. I hope to hear from ya guys soon. Jerry

[leolkfrm]

Try running a fresh ground to the guages and see if it helps

[HardRock]

Ya I was thinking about that also.....

Thanks

[crabtruck]

Welcome to the forum Jerry.
I figure if you have a drag car there are one or two things you already know,
but others read here too so I'll cover a few bases...

First, the gauge on dash that shows a mid-range of 8-16 is a VOLTMETER.
Not AMPS, totally different kind of gauge and wiring.
Second, unless you have an outstanding set of battery banks,
a little gauge movement with the turn signals is normal
and even more apparent w/ trailer.
Third, over and under-drive pulleys will not make a big difference with stock
electrical items when engine is high idle or better.

In the 92 I believe the gauge is measuring the system voltage at a fuse point under dash.
You did not say how far the gauge dropped when warm, but it is normal
for it to read near 14v when cold start and drop sitting at idle as engine warms.
Remember the alt initially is trying to recharge the just used battery and the engine slows as it warms.

Biggest thing you can do is clean each and every wire that comes from batt
and alt, at BOTH ends, and make sure the connection points are clean and tight too.
Don't forget the same is true for the invisible wire that is mechanically looking
like bolting on the alt - that's its ground connection.

The 13.69v is probably true and ok. A 160A alt will not put out even half that
in cold weather at slow speeds. If your loaded with stereo equip you need to go bigger.

[Chevy_Finatic79]

Crab, while we are on the subject what amp rating ALT is the best for TBI motors and big stereo components big amp big subs, DVD deck.
I thought you were doing good if you had a 100 amp ALT. when I ran my carb motor it only had a 60 amp ALT and I had a hi powered stereo system in that and it worked fine.
doesnt the higher amp ALT increase the amps in the circuits? which could get dangerous.

[crabtruck]

Increasing the size of the alt, even if you install a 300A,
would not change the amps in any circuit except the direct charge of the battery.

The amps actually generated at the alt are dependant on loads,
so a 300A alt may only put out 20A if that's all that is needed.
You might think of it as alts having an internal voltmeter
and it judges how much to produce in the way of amps
by checking if the system voltage (battery voltage) is high enough.

If you add loads to the truck (stereo stuff, winches or off road lights)
the load on the alt will increase, but none of the extra will be going
through the IP, ECM, tranny or backup light wires.
Properly wired, the additional loads have their own wires.

A TBI engine will take more amps than carb, but no so the alt would notice.
My stock 94 TBI K1500 could get away with a 40A alt.

Many times people confuse loud stereos with powerful or amp hungry.
How it sounds doesn't tell you how much it draws (amps) from alt.
Read the Lit for your stereo, add at least 125% of that to truck needs.
Don't use textbook power formulas because they don't include adjustment
for normal losses in signal and power conversion. Purely theoretical.
Bigger is generally better here, and many folks add an extra battery too.
Remember that @1500rpm or below alts produce poorly - 35 to 65%.
Cold takes a bite out of them as well. Ironicly, so does heat.
Different alts have different output curves as well, same as engines,
so find out what the curve is for yours at what temps, and stay within it.

A stereo (or any other load) needs more alt in the parking lot than on the highway.
Ways of checking if alt is getting it done is not having headlights dim
or system voltage ever drop below 13v with engine on.

Is a 100A alt big ? All relative, that's the stock alt on my '06 Matrix with cheapo stereo.
Maybe I have bigger headlights than you....

[HardRock]

Thanks for your input crabtruck....I have nothing but factory radio nothing after market at all.....I did check all those connections and everything did look good...maybe its all in my head and the gauge is just wacky...but I don't want to be in the middle of nowhere and have it leave me. I do a lot of traveling racing Nostalgia Super Stock circuit so....being stranded will be a BAD thing..Thanks again and anymore input would be great....

[HardRock]

Oh ya forgot to answer your question....if I have the light on and my dual electric fans kick in the gauge almost drops to 9....but the normal drop of just warming up is a tick or two off 14...hope this helps someone that can help me..

[crabtruck]

Sounds like you are ok on the warm up part. The drop to 9v, especially if very many seconds, seems out of whack. Might consider larger wires for the batt and alt group, and maybe go up in size on batt as well (rating not case size LOL). If you have that 9v at cruise speeds then you need to improve, if only at idle you need to watch over it (increase rpms) or the system will leave you in trouble. 9v steady is unacceptable.

[HardRock]

Hey CrabTruck!!!!....what do you think if I put another battery in the truck? Will it help or just be a waste? I tired of wasting money on stuff that doesn"t work. Thanks for your input too...just because I work on cars doesn't mean I don't over look the simply things....Thanks again for your help. My plan is to run off 2 batteries.