Car Gremlins

[Skip Talbot]

Alright, I've done some work on my car and I'm sure I've screwed something up somewhere, but perhaps one of you can point out my flaws.

I strung two 12-gauge wires off the positive battery terminal through a rubber grommet, one connecting to my 400W inverter and the other to a switch, which then connects to three DC outlets. I have a 30 Amp inline fuse close to the battery on each wire. I strung 12 gauge grounds from the switch and the inverter to a big bolt underneath my car, and the ground from the DC outlets to a bolt I found under the dash. They appear to be nice metal contacts connected to the chassis. I also installed a new radio, of rather low wattage (it was one of the cheapest models they have), using the existing wiring harness and ground.

Now, I have some strange gremlins in the car. The inverter, outlets, and radio work great but I'm blowing a 10 Amp dash light fuse. I've blown two, and haven't found a particular event that triggered it. My dash light dimmer switch also seems to have failed, and I was thinking they might be related. On my last chase I was stopped at an intersection, and my speedometer started moving erratically, but resumed normal operation as soon as I started moving. It only went crazy on me when I was stopped, and hasn't acted up since the chase. Also, my radio is not getting as good as reception as the old unit, although I believe that might just be the quality of the unit. Any ideas or newbie mistakes you think I've pulled?

 

[Dennis Sherrod]

Couple of possibilities I see that may cause the critters to come out. Are the 12 V DC plugs new or were they existing already? If any are existing and you double wired into them, that may cause a problem. Second and maybe most likely, it is the radio as you don't have any problems with the inverter, correct?
If this is so, disconnect the radio and see if the problem still happens. If not, there is the problem. Then you have to find out if the radio wiring harnesses actually match or just happen to plug into each other. I am thinking there is something in the wiring of the new radio and the existing wiring harness that don't match.

 

[John Erwin]

Agreed. Most radios have an input for the dimmer circuit from the car and since you're having lighting problems... I think we see a pattern.

Also.. I would strongly advise running a separate ground wire direct from the battery to the inverter; but make sure you fuse that wire too.

 

[Chris Gullikson]

Probably totally unrelated to your radio issues, but I agree on running separate ground wire from the battery. I do not like using chassis grounds for equipment as RF noise has a much better chance of being introduced into your equipment. Keeping the battery and return wiring close together and better yet, using twisted pair wire will help reduce RF noise on sensitive computer equipment.

I would also replace those 30 amp fuses with 20 amp fuses. 12 ga wire is rated at 20 amps and should be fused at 20 amps. That short of distance it will likely easily blow a 30 amp in the event of a short circuit but a 20 will blow quicker and a high resistance short may not blow your 30, creating a fire hazard.