Weird electrical issue

[Zap]

Okay, I am getting to the point where this no-start issue is just intolerable anymore. The random nature of this problem has plagued the '94 for too long.

Here's the scoop - it is generally okay, but on random occasions the battery appears low as the dash lights are dim and when you go to start, you get the chug or click. The strange thing is it usually comes out of nowhere and will have been working fine for some time.

Voltage is fine when the car is running - the alternator appears to be okay. Can a bad battery cable cause the battery not to properly charge and eventually wear down? Also, does anyone have a diagram of the system or can you comment on the sense lead that affects the battery light on the dash? Does it have another purpose besides triggering the idiot light? The plug just wiggles too much, and if wiggled the wrong way the battery light stays on.

Also, can anyone comment on the replacement cables from AutoZone? They have some oversized cables that look fairly nice.

 

[hawkeye18]

I would highly recommend replacing all of the charging cables on the car. Battery to starter, starter ground to battery ground, and starter to alternator. Known as the Big 3.

And yes, a bad cable - and, more likely, a bad battery terminal - can cause this random no-start situation.

As far as the plug goes, one of the wires goes to the positive terminal via the idiot light. It's a simple competing ground circuit. As long as the voltage from the battery and voltage from the alternator are equal (which they should be), voltage doesn't go anywhere. As soon as one goes weak or strong, or there is an imbalance, voltage will flow, lighting the lamp.

The other wire is far more important. This is the sense wire, and it goes from the battery positive terminal directly to the plug (via a fusible link or two) and that wire tells the alternator what voltage is coming off the battery - this tells the alt what to put out. e.g. if the alt sees 10v, it ramps up to maximum power, but if it sees 14.5v, it pulls it back. If that wire is disturbed or intermittently open, it can cause problems.

Rockauto sells replacement connectors that you can use. As far as replacement cable goes, I would recomment AT LEAST 4 gauge; I really wouldn't go any smaller than that. Stock cables are 8 gauge IMHO. Too small. I have 0 gauge wire in my car, and many people use 00 gauge with good result. The bigger the cable, the lower the resistance and current carrying ability. One guy I know has 000 gauge in his tacoma. Ridiculous.

 

[Kens1992mtxSHO]

Changing the battery cables is an easy and cheap fix. I second this recommendation. When I did mine they were corroded throughout.

 

[Zap]

Thanks for the confirmation - how difficult (long) of a job is it to replace at least the two cables that attach directly to the battery? I'm not sure if I can source the alternator to starter cable locally, and the car is acting up more and more.

Is there another name for the third cable since it has the fusible links in it? I see a "switch to starter" cable, but I'm guessing that is for something else. Of course the negative cables are not stocked locally....Ugh.

Can anyone confirm that the positive cable length is about 25"?

 

[hawkeye18]

IIRC (and I have posted on this before), I got 60" of cable and just cut it to match. I think one is 25" and the other is 24".

 

[the4biddendonut]

I think it's easier, when upgrading the big 3, to take the harness off the car and make a new one to match the old harness. It takes the guess work out of choosing battery cables. Of course you won't be able to drive your SHO to auto parts store.

 

[hawkeye18]

The hardest part of getting the harness out is two little metal arms that swing over it and clamp it to the radiator support. You have to a) find them and b) bend them back up. Other than that, it's a simple exercise of unbolting the two ends and yanking.

 

[Zap]

The harness isn't great, but it turns out that replacing the battery and the other cable clamp has it starting better than it ever has since we've had it! When I've got some free time over a weekend (and its warmer) I'll go back and replace the cables as well. Besides, now I've got another SHO that I can use to run for parts!