Tow vehicle electrcal hookup

RandandDoug wrote:
Talked with spartan and on my year moho the same fuses that operate coach lights operate trlr lights. Coach is working properly so it is wiring or a connector somewhere. The receptacle looks ok, but I think I will start with replacing it with a new one in case it has funked out. Doubt that is it but a quick and easy try. Then trace the harness as far as I can.
When using a tester, should I hook the power lead to power and then to different contacts while those are turned on, brake, turnsignal, tail lights and so on?

Whoever you talked to at Spartan is wrong. For the past almost 20 years, Motorhome chassis makers (Ford/Workhorse/Roadmaster/Spartan/Freightliner) have ALL separated the Tow plug fuses from the regular chassis lighting fuses. They have done this to prevent a TOW short from taking out the regular motorhome lighting and Brake lighting AND to split the current draw to separate fuses. Running BOTH systems on 1 fuse would require larger fuses(over 30 amp on each circuit) and LARGER gauge wiring to handle that larger load. I NEVER trust the fuse panels schematic. You either use a voltmeter or a 12 volt tester(best and quickest) and check ALL the fuses in the 2 or 3 chassis fuse blocks. Make sure you have the Ignition key ON. Your problem is you have a towable fuse/s blown somewhere. Doug

RoyB wrote:
ETRAILER has a couple of generic diagrams of what it should look like...

7-Pin Bargman Pinouts



Wire colour codes may vary from those indicated.

RoyB wrote:
ETRAILER has a couple of generic diagrams of what it should look like...

I picked one of those 7-way tester adapters from AMAZON that you plug into your truck 7-way connector and then you can do all of the truck functions and observe small led lights on the test adapter.

For me this was great as it eliminates any problem coming from the truck side... They make a 4-way test adapter as well...




All of my wiring fuses for this is on the truck side... The trailer does not provide any 12V power for the required DOT Trailer safety lights and functions.

Roy Ken

Or, get one that combines both:

https://www.amazon.com/Ultra-Tow-4-Way-Circuit-Tester-Model/dp/B00BINSI20

ETRAILER has a couple of generic diagrams of what it should look like...

I picked one of those 7-way tester adapters from AMAZON that you plug into your truck 7-way connector and then you can do all of the truck functions and observe small led lights on the test adapter.

For me this was great as it eliminates any problem coming from the truck side... They make a 4-way test adapter as well...




All of my wiring fuses for this is on the truck side... The trailer does not provide any 12V power for the required DOT Trailer safety lights and functions.

Roy Ken

I am assuming you have a seven pin or blade connector, each of those contacts has a specific location in the connector and a color wire schedule, not all installers use the proper colors so after getting the schematic of the vehicle connector you can start looking for the problem.

After verifying the fuses are good, you can start trouble shooting.

There is one contact that is chassis ground and six 12vdc outputs. If your test light is like most you have a wire with a clamp and a probe on the other end, connect the clamp to a known chassis ground, turn on the one of the flashers and see if the correct contact is hot. If it is, move the clamp to the assigned location of the chassis ground in the connector(you may have to use a nail held by the clamp to make contact with the connector). If it lights up, you know your chassis ground and the flasher is good.

Go back to the clamp on a good chassis ground and check all the contacts in order going around from the common pin either clockwise or counterclockwise.

If the assigned pin for the Taillights does not have power, check the back of the socket to make sure the contact screw is tight and the wire is not broken. This may require removing the socket from the RV.

If the wire and the holding screw or good but no power, follow the wire back to where the wire loom "Y"s off from the other lights and check there. Often there is a wire loom from the chassis to rear and a point where the taillights wire is connected to the taillights themselves. It's impossible to say how it's done unless you have a good schematic from the RV manufacturer, you just have to look for the taillight wire connection point.

If the wires follow a color code, it is easier for you but most likely they will all be one color except for the chassis ground.

Good luck and just disturb as little as possible and replace the loom cover as you finish with each check point.

Connect the lead from the test light to a good ground. Then use the probe to each of the functions. Function must be turned on. The test light will light up when voltage is present.
Locate drawing for connector from e-traler.

Maybe you can find an Electrical person to help you.

Talked with spartan and on my year moho the same fuses that operate coach lights operate trlr lights. Coach is working properly so it is wiring or a connector somewhere. The receptacle looks ok, but I think I will start with replacing it with a new one in case it has funked out. Doubt that is it but a quick and easy try. Then trace the harness as far as I can.
When using a tester, should I hook the power lead to power and then to different contacts while those are turned on, brake, turnsignal, tail lights and so on?

Cords do wear out if treated roughly or get dragged.
My bet would be on a bad fuse.
Have seen where the wires have pulled loose from the connector terminals.
Get a test light and check each fuse. Test for power on both sides.
Some rigs also have relays to operate the connector. The relay is energized by the tail light on MH.