Chazz

I replaced my left side marker light fuse (#40) but it blew again when the lights were turned on so I must have a short somewhere in that system. The last maintenance I did involved removal and replacement of the HVAC solenoid manifold module for troubleshooting the vacuum system. Is there some portion of the marker light circuit in the lower center console that I could have messed up in the process?

tveltman

Although I did not tear down the center console, I had this problem. The first thing you should check is the bulbs. The front turn signals are two filament bulbs, and if the bulb has broken down inside, or if the bulb has somehow backed out a bit and is not oriented properly, it will result in a short which will blow the fuse and kill your side markers/tails. You can pull the harness plugs at the CE panel to find the short. Check pins P11 and O15. These are the positive leads that go out to the front signal and side marker light, respectively, but save yourself some hassle and check the turn bulb in the front first.

Alan

I'd recommend the same - remove all the bulbs and see if it still does it? if no - its a bulb issue - if yes its a wiring issue...

Alan

Chazz

I pulled all the left side marker bulbs (front, back, side) but it still blows fuse #40. Any suggestions about what to check next?

Alan

What work have you done recently - everything...?

BTW you have 6 marker bulbs to pull - did you pull that many?

1 Rear side
2 Front Side
3 Front turn signal/marker
4 Rear outsdie lower segment
5 Rear middle lower segment
6 Rear brake light/marker

Alan

Chazz

I pulled all six bulbs, and in the case of the side lights, I pulled the spade lugs off so the fixtures were out of the circuit. The only recent work was the aforementioned removal and replacement of the airconditioning solenoids.

Chazz

Well, I’m baffled. I removed the front left marker light bulbs and fixtures, so I’ve only got the wires with spade lugs hanging out. The wiring harness appears to be in good original condition with no evident breaks in the insulation from the lights to where it goes through the firewall to the CE panel. With the battery disconnected, I get the following resistance measurements:

At CE board with plug O removed:

O15 to fuse #40 = 14.5 ohms
O11 to fuse #40 = 0.1 ohms

At plug O (removed from the CE board):

O11 to ground = megohms
O15 to ground = 0.2 ohms
O11 to lamp lead = 0.7 ohms (0.5 ohms long jumper)
O15 to lamp lead = megohms

At marker light:

Lamp lead to ground = megohms

This makes it look like O11, rather than O15, as shown on the wiring diagram, is the CE connection for the marker lights, but otherwise everything else is OK. So I button it up, put in a new fuse, turn on the lights and fuse #40 immediately blows. Rechecking resistances, the readings remain as before.

Alan

How are you determining the socket pin positions?? unless your headlights don't work you have the wrong pins...

Alan

tveltman

Disconnect the bulb control unit and repeat. Also, if the resistnace from O15 to ground is near zero, that's your short right there. Did you remove the CE panel or let something fall behind it at any point? Shorting out on the backside of the panel is not outside the realm of possibility.

tveltman

Alternatively, another approach here would be to remove every single bulb from the external lights and see if the fuse still blows. If it doesn't, add bulbs until it does, and you will have isolated your problem somewhat.

Mrmerlin

remove both side console covers and check that you have not pinched/misconncted any wires going to the lighter or the clock, or the shifter lights or HVAC lights also check that the console screws are not shorting into any harness.
Follow this path as the last thing you worked on will probably be the soulution

joejoe

My 86.5 had this problem and after tracking wiring to fuse box and pulling I decided to have someone with a bit more electrical experience go from there ( wiring behind fuse station was all grey, and there was a lot) Problem was found to be connector behind center consul to be bad. Bad part was spliced around and no problems since. Perhaps hvac work pulled or broke some wiring on yours.

Chazz

Alan, I understand pin 11 to be at the top left and pin 15 at the bottom left when facing the CE. Note that there is continuity between fuse #40 and the top left pin at plug location O.

All lights except the left marker lights work. With all left side marker bulbs out, the fuse still blows. I removed both side covers and inspected the area around the clock and lighter but could see no problems there. Also, I don’t understand how a problem there could blow fuse #40 which, according to the diagram, only seems to supply the marker light circuit.

Alan

Exactly my point - you have it backwards..

Pin 'X'11 is the bottom left pin pin 'X'15 is the top left pin, pin 'X'21 is the bottom right pin and pin 'X'25 is the top right pin. if you look on the socket - really carfully - they are labelled (molded).

Can you state it all again... with the correction

Alan

Chazz

Thanks, Alan. It’s not the first thing I’ve gotten backwards. Makes sense now. O15 has continuity to both fuse #40 and the lamps’ “hot” leads. The short is evidently intermittent. Where is bulb control unit? I’ll pull that before the next test.