tkbowers Report post Posted October 14, 2015 I have a short in the circuit for my back-up lights. The 10 amp fuse for this 12 volt circuit blows every time I put the transmission in reverse. After doing some testing, I believe that the short is downstream of the relay. I've tried to find the problem area with no luck, and believe that I should just abandon the existing conductor and run a new one from the relay, splicing into the existing line somewhere near the lights (back of the coach). I was unable to find markings on the existing conductor, but it appears to be 10 or 12 gauge. I've checked various wire sizing charts and get wildly different recommendations from one to the other...anywhere from 4 to 16 gauge. What percent voltage drop is acceptable for this type of circuit? I've seen anything from 2 percent (critical) to 10 percent (non-critical). I know that I could simply purchase new wire to match existing, but would like to verify this decision with some "higher power." I drive a 36 foot, 1994 Foretravel U-240, and estimate that the length of run for this circuit should not exceed 40 feet. Thank you in advance. Tom Sonoma County, CA Share this post Link to post Share on other sites
wolfe10 Report post Posted October 14, 2015 Tom, There is a gang plug that powers all the rear lights on your coach. I would disconnect it and see if the short that is blowing the fuse is "upstream" or "downstream" of the connector. Memory is a little vague, but remember it on the left rear side (open engine room door). If you don't have a wiring diagram for your coach, I am sure James Triana at Foretravel has one. I have not heard of any "fuse blew because of too small wire gauge" on Foretravel, so suspect short to ground. Most likely place is in the rear where water could have gotten in the receptacle and caused a direct short. Share this post Link to post Share on other sites
tkbowers Report post Posted October 14, 2015 Good suggestion Brett. I think I've seen the gang plug but could not get the darn thing apart. I will try again. What is a "direct short?" How would water in the receptacle cause a short to ground? Share this post Link to post Share on other sites
wolfe10 Report post Posted October 15, 2015 Tom, Each bulb socket has both a positive and ground connection. The bulb is a "resistor" between them. If there is water or even "wet dirt" between the two contacts, there would be a dead short (i.e. no resistance-- just a direct connection). Share this post Link to post Share on other sites
tkbowers Report post Posted October 15, 2015 Thanks! I understand. Share this post Link to post Share on other sites
lewengel Report post Posted October 19, 2015 If you have an old directional light flasher and amp meter, the kind where you hold the meter against the wire and it reads the current. You can jumper the flasher across the fuse, aligator clamps work good. It will flash (open and close quickly) causing current to flow to the short. Then slide the amp meter along the wires starting at the fuse and watch it . It should be bouncing back and forth at the same rate as the flasher. When you get to the short it will stop bouncing back and forth. Start looking there for the short. Share this post Link to post Share on other sites
tkbowers Report post Posted October 21, 2015 LewEngle, I like your idea. However, wiring, tubing, and piping are bundled very tightly in a raceway running lengthwise in the basement. I'm reluctant to disturb these lines too much for fear of creating a problem in another circuit or system. My vehicle is 22 years old. I disconnected both tail light assembly plugs. To my disappointment, again the fuse blew when I put the transmission in reverse. This tells me that the short is downstream of the relay and upstream of the plugs. Brett mentioned that there is a wiring harness further upstream of the tail light plugs. I found this device on the wiring diagram and as a next step will attempt to locate it on my coach. Share this post Link to post Share on other sites
rockylarson Report post Posted October 21, 2015 I believe when doing voltage drops in a DC circuit you need to count both directions of current travel. a 40ft run may need to be considered 80ft in your calculations. Also wondering if anything else normally comes on when you put the MH in reverse such as a rearview camera or backup beeper that might have a short to ground. Share this post Link to post Share on other sites
tkbowers Report post Posted October 21, 2015 Thanks Rocky. My wiring diagram shows no devices other than the back up lights. Share this post Link to post Share on other sites
wolfe10 Report post Posted October 21, 2015 Tom, I pulled out Foretravel 12 V wiring diagram B-2099 (7/21/92). It shows the back up lights as black wire with gang plug on left rear. That goes (still black wire) to ATEC DWG A4593. Sorry, I have no info on the ATEC or its location. If you still have your original manual, that may be detailed. You have already done the easy check-- disconnect the gang plug supplying the lights at the left rear of the coach. If the fuse still blows finding the ATEC and checking there would be the next step. Share this post Link to post Share on other sites
cauffield Report post Posted October 21, 2015 Brett, I have a 2009 Gulfstream Tourmaster Constellation 45g. I exhausted all efforts trying to find parts to repair the passanger side captain chair. It was made by Scope Technologies which have gone out of business. I called Gulfstream that exist now and they have no answers. I need to find out if a Flexsteel 6 position with a raised foot rest electric mechanism will work with my existing chair. Any help will be greatly appreciated. Thanks Lex Cauffield Share this post Link to post Share on other sites
wolfe10 Report post Posted October 21, 2015 Lex, Check with Flexsteel. They can tell you dimensions of the mounting and also what power is required (likely 12VCD positive and ground). Flexsteel 563 556 7730 Share this post Link to post Share on other sites
hermanmullins Report post Posted October 22, 2015 If the gang plug is disconnected and the short is up stream or down stream the dead short can be located with a continuity test light. Find a good ground and test each pin. When the light comes on that will be the wire that is shorted out. A simple test from my simple mind. Herman Share this post Link to post Share on other sites
wolfe10 Report post Posted October 22, 2015 Herman, Will have to give that one some thought. Since each wire in the gang plug goes to light bulbs, each will have a ground path through the light bulb. Yes, if the bulbs are removed, I can see this test working. Also, Tom is only having a short problem with only one of the wires (suspect it is black in his coach-- one year newer than our previous coach and the wiring diagram I have). At least no reported issues other than with back up lights. Share this post Link to post Share on other sites
tkbowers Report post Posted October 22, 2015 Thanks Herman. Brett is correct, I'm having an issue with the black wire. More tinkering today and will keep you posted. Share this post Link to post Share on other sites
tkbowers Report post Posted October 29, 2015 Wanted to let you know that I ran a new conductor for my backup lights. I verified no more blown fuses when I put the transmission into reverse! Thanks everyone for your help. Tom Share this post Link to post Share on other sites
wolfe10 Report post Posted October 29, 2015 Thanks, Tom for updating us. Yes, it is often easier to run a new wire than to check every inch of an old one. Isolate both ends of the old one and run a new one. Share this post Link to post Share on other sites
