1998 Ford F-150 Relay chatter, lights blink, spedo stops, bl

GARRENRK

MEMBER
1998 FORD F-150
V8
4WD
AUTOMATIC
168,000 MILES

I have had an ongoing electrical issue on my truck for a long time now. It has been progressivly worse. Started as once in 6 mo, to once or twice a week.
Intermittantly, the blower fan will run when truck is off and no key in ign, as well as relays chatter under steering wheel, 4x4 light blinks on and off, tach jumps. Again, when truck is off, no key in ign. While running, spedo may or may not work, cruise control intermitant, driver window stops working, pwr mirrors stop, 4x4 light blinks. This usually will kill the battery when it does it, then it will go a while w/o a problem. It's now a nightmare! (Today I even heard a whistle under passenger side under dash for about 3 min!) Any healp appreciated! Thanks!

Garren

3 Replies

RACEFAN966

MECHANIC
5,029 POSTS

Ok under the left side of the dash there is a module called the GEM module. This module is basicly a body control module. It controls most all the electrical on the truck other then the engine itself. Now if you have a digital multi meter or access to a scanner we can test this before replacing it. Let me know what you want to do and we will go from there.

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Friday, April 24th, 2009 AT 10:43 AM

GARRENRK

MEMBER
2 POSTS

I have a multi meter and I have a basic OBD-II reader. If I need to, I can have a friend run his scanner on this if that is the best way. At the moment, the truck is fin, other than the Check Engine light and the Airbag light blinks, then stays on. The OBD is a 500 now, and the Airbag light blinks 5-2. Let me know what next! Thank!

Garren

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Friday, April 24th, 2009 AT 3:54 PM

RACEFAN966

MECHANIC
5,029 POSTS

Ok lets start with a simple test on the gem to datalink ok. First I need you to find the GEM module to the left of the steering column and unplug it and then using your ohm meter check the ohms of the light blue wire with the white stripe from term number 25 on the gem to term number 7 on the data link connector. If less then 5 ohms then that part is good now plug the gem back in and with you code reader get the codes and get back to me with what codes the truck has stored so I see what that is telling us ok. Here is pic of the GEM connector and the Datalink connector so you know what terms you are checking the resistance on. Get back to me with what you find so we go from there ok.

Here is the GEM connector.