good tip, where is the relay located? near the fuses?

EDIT- I can not find ANYTHING in the manual about a brake light relay

 

in fuse box , see the 2 rectangular gray block looking things , ones starter relay and ones brake relay ,some manuals call it a system relay , you should be able to hear it click when you put brakes on

 

looks like this
http://www.ebay.com/itm/Standard-Mot...c1fddf&vxp=mtr

 

Only the starter relay is here

 

pull the brake and see if it clicks , because that's where brake system relay shows to be in my 2001 hd manual

 

Check the rear stop lamp switch:

Remove the two wires from the terminals on the switch, touch the probes from your ohmmeter to the terminals, and see if the switch is working when you step on the pedal.

Check the front switch:

Disconnect the connector for the right side hand control switches. Touch the probes from your ohmmeter to the orange/white wire and the red/yellow wire, operate the brake lever and see if the switch is working.

I don`t see a brake relay in the brake lamp circuit on the 03 Dyna wiring diagram.

 

If you are not burning wires or blowing fuses, it sounds like you have a corroded or bad connection somewhere...or that is a normal situation like a solid-state switch providing a low potential to the circuit...you will read full line voltage until you put a load on it...a real common gotcha when troubleshooting with a voltmeter.

 

I took a quick look at my wiring diagrams for your model and it shows that the power routes from the fuse via the orange and white wire to a common point that then connects power to the the two brake light switches in parallel, probably under the seat somewhere. The power goes to both switches' common terminals and then out the normally open terminals via the red and yellow wire to another common tie point, also probably under the seat. Then a single red and yellow wire goes from the common tie point from the normally open termals to an inline connector that connects to the rear wiring harness that routes under the fender to the rear light socket. This allows either switch to energize the circuit to the real brake light so unless both switches are bad, then they are not your problem.

Find the red and yellow wire going to the inline connector where the rear harness connects before going under the fender. Check real good and make sure you don't have a bad or corroded contact. If it all looks good, use a jump wire with two T-pins on it. Slide the T-pins in the back of the connector alongside the wire from the switch side of the connector and connect the other end to the rear brake light socket and see if the light works. If it does, then your problem is from the connector to the rear light. It could be a broken or damaged wire under the fender.

If jumping from the switch side of the connector to the brake light socket doesn't light the brake lights when you put on the brakes, then you will need to check with a test light to see if the switch side of the circuit is able to handle the current load for the light. To do this, you will need to connect one wire of a test light to the red and yellow wire at the brake switch side of the connector that connects to the rear fender harness and the other wire to the frame ground and see if it lights when you put on the brakes. Do not trust a volt meter for this because you need to put a load on the circuit. You may well read full line voltage with a voltmeter with no load on the circuit even though the circuit cannot carry the current load of the lamps.

My bet is a bad wire or problem with or at the inline connector...

I hope this helps.

Good luck and let us know what you find.

 

I have not seen if you have power at the Brake Light Switch

 

The red and yellow wire comes from both switches...he said that he read full line voltage with the rear brake light not in the circuit. That indicates that he is getting some power there but is a bad connection somewhere and the circuit cannot carry the load of the lamps. The bad connection could be the supply side from the fuse.

Check both terminals of the rear brake switch using a test light and frame ground. One terminal will be the common terminal and the light will work if power is present at the switch from the fuse and the other terminal is the normally open terminal and will light the test light if the switch is working properly when the brake pedal is pushed. If the power supply side cannot carry the load, the light will not work on either terminal.