Strange Defogger problem -
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post #1 of 3 Old 10-19-2017, 08:35 AM Thread Starter
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1999 TJ Wrangler 
Join Date: Sep 2008
Location: syracuse
Posts: 275
Strange Defogger problem

ok so i have all the factory wiring and the hardtop wiring matches the jeep. i have a 10 wire hardtop. now the defogger wont turn on.

however if i jumper the No 86 terminal on the defogger relay in the PDC under the hood to the ground on the battery, my rear defogger turns on and stays on and the rear window gets warm.

the wire on the back of the No 86 terminal is a Light Blue wire with a White Stripe. Mitchels 1 says that wire has to go to the ignition and runs through a splice above the engine, which is those two large plugs.

my mechanic friend suggested running a new wire and switch, which would bypass it all as well as the timer. that would be a last resort so id like to try and figure why the factory wiring isn't working.

thoughts? helpful comments? tips? tricks?

99TJ 5.2V8 ax15 2.5lift dana30/44 Lockers 410s 35s AtlasII bellyup skid & winch
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post #2 of 3 Old 10-19-2017, 09:09 AM
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2014 JK Wrangler 
Join Date: Oct 2017
Posts: 8,464
why not run LT/WT wire to rear defoger control, instrument cluster C1 #3 keep timer?
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post #3 of 3 Old 10-19-2017, 04:29 PM
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2005 LJ Wrangler 
Join Date: Mar 2011
Location: Trails of
Posts: 4,340
Mitchell is incorrect.

That light blue/white wire gets grounded by the timer in the cluster to close the relay & send power to the defrost element. The timer is activated by hitting the momentary defrost switch. If that is not happening either the switch is not sending the momentary ground signal to the timer or the timer is bad, assuming everything is wired correctly & the wiring is good. The timers are known to fail & it is possible that the switch is bad so some troubleshooting is needed.

The more common thing seems to be a bad timer. There are timer relays available to bypass the one in the cluster if needed. You can’t run a wire from the relay to the switch since the switch is a momentary switch & when you release the switch it turns off.

Good info here. Note posts 24 & 32

Here is the page from the ’99 FSM to see how it is wired.
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99 Rear Defrost.jpg  
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