Strange Electrical Things

[j57little]

OK, please try not to laugh, but I am having electrical issues. I wanted to upgrade the alternator so that I can run electric fans on my 66 Coronet. Everything seemed to be working fine, but then I noticed my accelerator pedal smoking. I have been accused of a lead foot, but not one on fire. The throttle cable burned through where it comes in contact with the firewall. One might suggest a massive power surge, but everything is working. The alternator gauge did surge momentarily after the throttle cable burned through, but even that gauge returned to normal and is still functioning. Something had to be drawing a huge amount of current, but I can't find what it was. Aside from the fans that I added (that still work fine) the only unusual thing was that the headlights were on. A bad switch might be indicated and since the accelerator pedal is relatively close, it might have been the closest weak link in the circuit. Any advice on likely culprits would be most appreciated.

 

[440roadrunner]

Easy, "probably." Poor grounding

Normally, with a factory battery, the battery is "main" grounded right to the engine, with smaller auxiliary straps / wires jumpering from the engine to the body. Anything grounded to the body, such as headlights, stereo, AND FANS needs an "upgraded" ground back to the battery

The "more stuff" you have turned on, which is all grounded to the body shell, the LESS likely it is that you have a good enough ground from the body to the engine / battery.

I use what's called a "starter cable" IE "ring to ring" battery sized cable. you can buy them different lengths. Look at the bolt holes for the alternator on the pass side head. Those same unused holes are on the REAR of the driver side head. Get yourself about a 1 ft starter cable and the appropriate short bolt, and bolt the cable to the rear of the head, then to either a nice scraped place on the firewall, inconspicuous, or maybe such as a master cylinder stud.

ALSO PLEASE READ this great "Mad" article

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

Even if you don't do this mod, it points out the weak points in these old girls. Be aware that "Ma" knew this. On cars with larger (60-65 amp) alternators, there was a mod called "fleet taxi police wiriing" which essentially routed larger ammeter wires through the firewall and AROUND the bulkhead connector. If you look in some of the shop manuals, it is there.

 

[Blackbird73]

X2 that can only be a bad ground

 

[badlite]

absolutely a ground problem, make sure you have a good ground from battery to body and goo ground to engine. 75 to 80% of electrical problems on cars is due to poor ground.

 

[j57little]

Thank you for this thoughtful reply. Having spent thousands of hours in electrical systems training on cars and having been in the auto industry for 25 years mostly developing electronics and electric vehicle stuff, the basics alluded me on this one. A good ground makes sense, but I never would have imagined the grounding strategy to be so deficient on these old Mopars...until I read the MAD article. Outstanding! I'm going to be adding some better grounds...right now!

 

[440roadrunner]

You're welcome. Easy to get "tricked."

I used to have an 86 Ranger V6. On that thing, the ground goes from the battery to the frame via a "T" terminal right in the cable, then goes on to the engine. One day it would not crank. The headlights remained bright, but it would not crank. WTF? Anyhow the ground cable was good down to the frame, but had corroded inside the insulation immediately after the T terminal on the way to the engine. So the lights, etc, worked, but the engine was not grounded.