My voltmeter "bounces" when cold and sporadically. I have installed a new alternator because the old one was on it's way out. Also installed a new Interstate Megatron battery so it doesn't wreck my new alternator. (old battery failed a load test)Still my volt gauge bounces sporadically. I have a Jensen 300 watt amp running a 10" kicker sub also installed. any ideas what is causing this "bounce"??

 

You have a bad connection somewhere. Clean the terminals and cable ends particularly the plug in that connects to the alternator. Use some dielectric grease on all the connections. Mine did the same exact thing, the guage bounced and the headlights flickered. Turned out that I had a bad ground where the main cable connects to the engine. Cleaned it and the truck starts easier, runs better, and no more bouncing battery guage.

 

I like johncfox's ideas, all of those battery cable end connections need to be clean, bright & tight.

If that doesn't do it, consider running this puppy by your favorite autoparts store for a no cost, in vehicle, electrical system check up, via their portable electrical system tester. Properly used, it can load test the vehicles electrical system with everything in place & will likely spot the problem.

Let us know what you find.

 

I cleaned all the grounds I could find. Now it seems only to do it when it is cold. I am going to try a new negative cable and ground it to the block somewhere else. It's currently (ha ha ha) grounded to the lower starter mounting bolt.

 

Try using a good large wire gauge/low reistance, jumper cable & parallel connect the B- & B+ battery cables, one at a time & see if the problem will clear. The battery cable, or it's connectons that's parallel connected with the jumpers, when the problem clears, is the suspect.

This way you can do a good, quick, easy, function test on each battery cable, ground strap, ect, without throwing money at the problem, on a hunch.

Doesn't Canadian Tire do, no cost, in vehicle, electrical system testing, with a portable tester????

 

I tried pawpaw's trick with the booster cables. Went from negative post to one of the exhaust manifold studs and it cleared it up instantly. I've made a temporary ground from neg post to motor mount with 8 gauge wire. Here's the kicker; priced out a new Negative battery cable from Mazda ( it has 3 other leads off of it) $69.00 for a &^%&* battery cable!!!! I like the OEM cables, all the leads are integral with the battery connection. I can get a universal one, but then I have to connect the other grounds to the post with ring terminals, just another place for corrosion to start. I will have to see what i can find for an alternative cable I guess.

 

Maybe check the local salvage yards, or scan our forums vendors for a new cable, bet their price would be better than $69, even with shipping!!!!

 

I finally found an alternative to buying an OEM cable. Went to the local heavy duty parts store and bought solder on terminals and battery post ends.. They come with solder slugs, you cut the cable to length, put the terminal in a vise, drop in the slug, heat it with a propane torch until it melts. Add a a little flux to the cable end (i use liquid flux designed for electronic soldering) Stick the cable end in and let it cool off. Heat shrink the connection and you're done. Total cost $ 32.95 cdn and a little time.

 

Sounds like a good fix, has it solved the origional problem????

 

Yes, it has fixed my problem