Allpar Forums banner

1 - 10 of 10 Posts

·
Registered
Joined
·
164 Posts
Discussion Starter #1
I was troubleshooting an electrical problem in my B300 RV when I created a new trouble! :frusty:

While checking running lights to see if they worked, I bumped the unfastened instrument cluster and its electrical circuits hit the edge of the metal dash housing. Bzzzapp! The running engine "stumbled" but kept going. I shut it off, examined everything for burned or otherwise damaged components (including fuses - none blown) and tried to start the engine. Nothing - except a small burn mark at the point of contact with the dash.

This is one reason why I don't work as an automotive electric technician. :facepalm:

Everything one would expect to work with the switch in the "run" and "acc" positions works. Good thing the short lasted less than a second.

I got out my multitester, removed the ignition, and tested it according to the instructions in the Haynes manual.

IGN 1, key ON: FAIL (However, with the key turned to "start," current passes through)
IGN 2, key OFF: Pass
ACC, key ACC: Pass
ST(ART), key START: Pass (!)

The Haynes text reads in part, "[Turn key to Run], connect the [ohmmeter probes] to the B (battery +) terminal and either of the I (ignition) terminals - there should be continuity." Either terminal? Does that mean that only one or the other needs to allow continuity? I'd think it'd be both. Any thoughts?

Personally, I hope the internal switch connection is what got "fried," because it's easier to replace the switch than find wherever the circuit got broken.
 

·
KOG
Joined
·
6,994 Posts
The fact that you have power in every position but IGN does indicate a zapped switch. The other failure from a major short would be the fuseable link from the battery, but that would kill every thing.
 

·
Registered
Joined
·
6,042 Posts
The reason you get power on IGN1 seems to be that it is backfeeding from the start when it is engaged. You did not give the year but I expect you have a blown switch.
 

·
Super Moderator
Joined
·
21,353 Posts
There are several fuseable links at the LF firewall. I would want to rule any of them out as being open first. The one that you pull gently on and stretches would be the bad one. Avoid poking through wire insulation with a test probe.
The switch may be easily taken apart for inspection, look for any burnt copper contacts. Although these switches do wear, they are usually pretty robust with a current surge.
The cluster ammeter wires handle high-current with fat wires and may be what shorted. Does the ammeter pointer still work?
 

·
Registered
Joined
·
164 Posts
Discussion Starter #5
Dr. Dan's Caravan said:
IGN 1, key ON: FAIL (However, with the key turned to "start," current passes through)
IGN 2, key ON: Pass
ACC, key ACC: Pass
ST(ART), key START: Pass (!)
All with key OFF: Pass

The Haynes text reads in part, "[Turn key to Run], connect the [ohmmeter probes] to the B (battery +) terminal and either of the I (ignition) terminals - there should be continuity." Either terminal? Does that mean that only one or the other needs to allow continuity? I'd think it'd be both. Any thoughts?

Personally, I hope the internal switch connection is what got "fried," because it's easier to replace the switch than find wherever the circuit got broken.
The above quote from my own post is corrected information. I had typed "OFF" by mistake in the IGN 2 entry.

I bought a replacement switch thru. online order from O'Reilly Auto Parts (great service and fast, by the way). Before I went through the trouble of installing it only to discover the problem is something else, I used my multitester on it and compared with the existing switch. The results are identical. The only way to tell the two switches apart is the new one looks cleaner (no suprise).

ImperialCrown's suggestion about a blown fusible link seems the most plausible alternative explanation. The rub is that I only see one in the expected location near the firewall. And that one is between the positive battery and the whole bloomin' electrical system, so that ain't the bad one.

I'll send a photo when I get back to the RV, probably when the weather warms up. No fun working on a non-urgent problem in the subfreezing temperatures.
 

·
Registered
Joined
·
164 Posts
Discussion Starter #6
Left out that the ammeter gauge does work.
 

·
Registered
Joined
·
1,805 Posts
IIRC, my 87 B250 had fusible links between the brake booster and firewall. Not sure what year your machine is.
 

·
Super Moderator
Joined
·
21,353 Posts
1976? A Dodge B-van electrical service manual/wiring diagram may help although many RV upfitters add their own wiring that can be more difficult to figure out.
 

·
Registered
Joined
·
164 Posts
Discussion Starter #9
Dr. Dan's Caravan said:
I was troubleshooting an electrical problem in my B300 RV when I created a new trouble! :frusty:

While checking running lights to see if they worked, I bumped the unfastened instrument cluster and its electrical circuits hit the edge of the metal dash housing. Bzzzapp! The running engine "stumbled" but kept going. I shut it off, examined everything for burned or otherwise damaged components (including fuses - none blown) and tried to start the engine. Nothing - except a small burn mark at the point of contact with the dash.

This is one reason why I don't work as an automotive electric technician. :facepalm:
Truth-is-stranger-than-fiction update: On a rare warm day today I put the switch back in since it wasn't the problem. On a whim I hooked up everything after looking at the Haynes manual, lest the switch "failure" had been due to forgetting to put back a connector and therefore leaving an open circuit. Well...the starter cranked and the good ol' 360 fired right up.

I took the RV to a gas station, added some fuel (the gauge wasn't registering), went to leave...no start. To make a long story mercifully short (leaving out the part about trying to hire a tow truck), I tried, out of desperation, starting it with the shift lever in Neutral and success. (?!)

More funky stuff: the flashers flashed when the head lights were on (it was right around sunset) and the turn signals wouldn't work. I had to switch 'em off so I could signal my turns. Good thing it was still bright enough that I didn't need runing lights and I only had to drive a couple of blocks back to the storage lot.

Since the hazard/turnsignal problem is new, I'm wondering if maybe that accident with the panel hitting the metal damaged the circuit board and created some weird short-circuits.

I put electrical tape over the edge of the metal dash opening to avoid repeating the mishap during future troubleshooting. Could be like shutting the barn door after the horse got away. Oh what fun this is going to be to follow all those wires in the dash!
 

·
Registered
Joined
·
1,083 Posts
Physically and electrically check every fuse you can find. The brief short may have simply blown a fuse and you may be getting current back feeding through another circuit causing the unusual electrical issues. Sometimes a fuse will "blow" with a break so small that it's almost undetectable by eye. If the fuses are all good then a bad fusable link is the most likely culprit. Most passenger cars have more than one and they do differ in their current capacity rating. Typically they're color coded by wire gauge and the insulation is usually softer and more pliable than the regular wiring.
 
1 - 10 of 10 Posts
Top