Brake light out

[bkuhr]

on 83. Did not notice when last was working (maybe last year), but just finished fuse upgrade and added running/fog light and stebil horn. Running tail light works.

Also added 4 relays

1. headlight and acc bypass ignition key switch(at fuse panel){to limit load on key switch}

2. fog light

3. horn

4. spare, not used at this time

 

checked foot brake switch and have 12v on1 side, and 12v on other side when either foot or handle brake applied. 0v when switch normal. CMS no indication of problem.

 

pulled and replaced both brake bulbs, no change

 

removed truck and got to rear 3 wire connector at brake light

12v on blue(running)

12v on yellow(brake) when brake applied//??4v when brake off??

good ground on black

 

temp jumpered power to yellow side of connector and bulbs worked(sockets ok)

 

semi perm installed jumper from rear brake switch output to yellow at brake housing

now all works ok, but have CMS fault(tail lts) only when brake applied

 

Thinking lack of current(amps) to drive brake lights due to corrosion or partial open even though I have 12v at brake housing. Unsure why I have 4v when brake off(corrosion )?

Probably need to pull seat (if I can remember how) and check underseat harness, but I am suspecting problem with the CMS(such a pain to pull dash)

 

any other ideas?

[mbrood]

The seat is held with 2 10mm bolts, each side about where the passenger's legs would be.

 

As you've probably seen... The switches send 12v to CMS when applied, the CMS then sends the 12v to the lamps. Since the running light works, the common ground is good... so you narrowed it down to the CMS and hopefully you just have a grungy connector limiting current and that needs attention... otherwise... ya gotsta get a new one... in my opinion.

[bkuhr]

The seat is held with 2 10mm bolts, each side about where the passenger's legs would be.

 

As you've probably seen... The switches send 12v to CMS when applied, the CMS then sends the 12v to the lamps. Since the running light works, the common ground is good... so you narrowed it down to the CMS and hopefully you just have a grungy connector limiting current and that needs attention... otherwise... ya gotsta get a new one... in my opinion.

 

current passes thru the coils in the CMS to active the magnetic reed switches between the coils for the warning lights. Most likely solder connections melted and can be repaired, but it is such a pain to get the CMS out:crying:

[dingy]

Brake lights work when you jumper from brake switch to connector? correct. This eliminates light housing and three pin connector. Next there is a 6 pin connector under seat on left side. It should be a Yellow/Black wire from the three pin to the six pin connectors. Check continuity at this one.

 

Next stop is the CMOS connector, looks like center top pin is Yellow/Black.

 

Feeding into the CMOS from the brake circuits, it is a Yellow wire. Looks like bottom row, second in. You should read 12V+ when brakes are activated on this one.

 

Only thing left is inside the CMOS.

 

I have pictures that show bypassing the reed switches if you have to.

 

Gary

[bkuhr]

I have pictures that show bypassing the reed switches if you have to.

 

Gary

 

Been thinking about mod for CMS anyway.

 

Remove all 4 coils and all 4 reeds. Jumper original coil pcb pads to nearest reed switch pcb pad. This allows orginal external IN and OUT wires to work where the reed switch was.

 

External CMS on MC wiring cut each IN and OUT wire and and splice to each other on MC side. On CMS side of cut external wiring, splice to extend all wires cut with small gauge wire(24ga 4 pair telco wire), as these will now be used only for signaling and not carrying load power.

 

With as above, CMS warning lamps effected,

H head lamp; L head lamp; tail lamp; brake lamp,

will be inop and not display any warning-simular to bypass mod

 

but,

 

now I can install a photocell to detect each of the above lamps is lit, and photocell will drive small signal relay wired to above extended CMS wiring, thereby giving true warning capacity back, even with LED or HID lighting:)

 

A little more specifically, also need to have 12v applied to IN side of where reed switch was when lighting circuit is on, and relay will apply 12v at OUT side of reed switch. If 12v on IN and 0v on OUT=alarm light. 0v In and 0v OUT=no alarm(light circuit off), 12v In and 12V OUT= no alarm(light circuit on and working properly)

 

Watch ya think?

[dingy]

Sounds like it might work.

 

When I installed the dual head lights, I just jumpered out the reed switch on the CMOS for the Hi & Low beams. This eliminated my warning CMOS light and it allowed me to directly wire the headlight power to them and remove the voltage drop inherent in the light gauge wire in the stock system.

 

Gary