Battery connections were put on backwards

[MSN Member]

From: kevincompton
Sent: 2/11/2008

I have '78 Winnebago Brave

Ok so whoever owned this thing before me switched the colors and well, I wasn't expecting that and there you have it.

Now it wont do anything, no headlights nothing, yet the battery is still plenty hot. So what do I do now? Never had this happen before.

[denisondc]

Sent: 2/11/2008

If your Winnebago is on the Dodge chassis - there is at least one fusible link in the wiring - and I expect it would be burnt/blown. If its on a Chevy chassis it probably has one or more also.
On mine the one end of that fusible link connects at the starter relay - where the positive battery cable stops. The other end of that fusible link feeds the red wire that runs up to the ammeter. From the ammeter it goes to the rest of the chassis wiring: Including the 'output' terminal on the alternator. This output terminal is always connected to the rest of the wiring, but normally draws zero current because of the diodes in the alternator that rectify the alternating current into direct current. If the battery were connected backwards, those diodes would amount to a short circuit. And the fusible link would go out immediately, effectively disconnecting everything from the battery.
As for other things that might be affected: The 78s would have an electronic ignition module. I dont know if it is protected from a reverse voltage. It might or it might not care about it. If you had a modern radio with a 'memory' lead, that might be affected, it would depend on whether a reverse volts protect was built into the radio. I don't know if the diodes would have been injured by the reverse voltage - Im inclined to believe they could handle the voltage, as they are fairly tough, but I don't know.
Its possible nothing but the fusible link is damaged, but you would want to check the ignition module I think. The fusible link is just a short (6") length of wire that is 2 AWG grades smaller than the rest of the circuit: 12 gauge instead of 10 gauge for instance. It has a special insulation that wont burn, just melts. This is to prevent starting a fire.
On my Winnie that fusible link is on the drivers side of the motor, down low more or less beside the starter. There are replacements made, though I have been known to just solder in a length of the right sized wire, and not worry about the insulation catching fire in the future. Before you replace it, I would connect the two ends of the wire through a low 'resistance', like an old headlamp bulb. Then with the battery connected, that bulb should only light up when you turn on the motorhomes running or headlights, or turn on the ignition, push on the brake pedal, etc. If it comes on as soon as you reconnect the battery - its maybe a shorted alternator.
I don't know what the effect on the voltage regulator would be. Maybe slantsixness knows - he is far deeper into mopar knowledge than I am.

[ClydesdaleKevin]

Sent: 2/12/2008

If you have a Chevy chassis, then there are 2 chassis fusible links, and if either blows, the whole system shuts down.  On our 77 Itasca with a P-30 chassis, they are located right below each bumper, front and rear.  They stick out a little from the coach...you can see them without looking under the bumpers, just a little half-loop of wire.

Kev

[Slantsixness]

Sent: 2/12/2008

Ouch. That sucks.

So you made a mistake:

Here's what probably happened: (if it was hooked up for less than 5 minutes)

(If this is a dodge chassis)

Your Alternator, regulator and Ignition module are susceptible to damage. The alternator diode pack (in the rear of the case), for certain, and possible the starter's internal relay. It really depends on how long this was left hooked up reversed.

There is a fusible link on the starter relay, with a little tab on it. Remove it and reconnect that wiring. There may be 2 or 3 of them there, remove them all.

Go to your fuse box for the chassis. Remove the radio fuse, ACC fuses and cigar lighter fuse. (you're disconnecting "ELECTRONIC" accessories, that are immediately susceptible here)
Your lighting circuits (park, turn, stop, headlights..dash...etc) are resilient enough to still be ok. Your gauge regulator may be toast though, at least the Capacitor on the back of the dash might be damaged, if not the whole gauge regulator circuit.

Now, hook up the battery and see what works. (If it cranks but no start, try an ignition module or the ballast resistor).

The starter relay is located on the frame rail by the starter.


If the chassis starts and runs.. slowly check all the circuits, starting with the alternator and charging circuit, then reinstall,(one at a time) the ACC and BAT fuses.

If it doesn't start at all, you might have missed another fusible link, possibly in the interconnect at the floor, which is usually behind the gas pedal, and under a cover..

There's more help if you need it, but it's usually not that bad... it just CAN be this bad... doesn't have to be.