91.5 Electrical Gremlin

[BSeyler]

I found a 91. 5 CTD today and picked it up for my son. He is currently deployed to Afghanistan, so I did the leg work for him. It's a one owner pickup with 190,000 miles. The owner is 70+ and just didn't need it any more. It has an automatic transmission and is totally stock. The only thing I can find wrong so far is that it has a couple of electrical issues.

When driving, at times the 'wait to start' light flashes for a while and it won't shift into OD. When the light is out, it shifts fine. There's no pattern to the light coming on. It was 98 degrees today and the light would simply flash several times intermittently while at highway speed, then go out for a while, repeat, etc.

The blower for AC/heat is also having issues. There is no power coming to the blower switch. I checked for blown fuses and they are OK. There is power coming into the control panel, as the compressor does engage and functions correctly. You can feel the cool air being pushed in when cruising, I just have no power to the blower. I hooked a jumper wire to the plug and have all three speeds on the blower, but no power to the switch, if that makes sense. In the morning, I will finish pulling the panel out and see where power is supposed to come from.

I swapped the ignition switch out with a spare, but no change. Thanks and any ideas will be appreciated.

Bud

 

[Nyoest]

I don't have a specific answer but a good start might be to clean and fully check the battery cables, their connections to the starter and block and any other grounds you come across. I ve seen weird things due to nothing more than corrosion.

Should make a for an even better homecoming for him! Be sure to let him know there are still plenty of people that appreciate the job he has done to keep us safe.

 

[BSeyler]

Nyoest,

Thanks for the reply. After I went to bed last night, I of course couldn't go to sleep because I was still trying to sort this out. Good point on the grounds and I will check them. I can't imagine there would be two power supplies to the heater/AC control, so am wondering if there isn't a corroded connection. I also wonder if there isn't something going on with the IAT sensor. I thought I'd unplug it and see what happens.

My son is pretty tickled over getting this rig. The first time he was deployed, he had to go stand in line on a certain day for a phone, and that's only if they were in camp. Communication was hit and miss. Now, he lives in a real building and has internet in his room! I sent him a message on Facebook that said, "Congratulations, you own a pickup" and the phone rang in about three minutes. I'll pass your appreciation on to him. I just got a son in law home from there last month and am looking forward to May for my son to be home. I think I'll park his pickup in the driveway and put a big ribbon on it.

Bud

 

[HHhuntitall]

Very nice. As a once young man, I can appreciate what it would be like to come home to a truck of my own in the driveway... ... especially after being at the back door to he**.



Now, for your truck problem, using a test light probe, there is a set of fusible links, they look like a power tree, one big wire coming in and four going out, on the driver fender, check to make sure there is power getting through all of them..... and there's power getting to the fuse under the dash. If it has power there, the problem lays from there to the blower motor. There is a reisistor on top of the A/C unit, behind the glove box(tan in color, above ABS computer), which controls the blower motor speeds. Usually they'll still work on high, but it could have burned completely up, not allowing power to get to the switch... ... .

 

[BSeyler]

HHhuntitall,

That nagging little voice in the back of my head kept telling me I was overlooking something, so I went back and tested for power coming into the fuse panel. Sure enough, the hot side of the heater fuse was dead. (All I had done last night was check the fuse, but didn't check for power. Can't believe I'm this age and made a rookie mistake like that!) I unplugged it and put a jumper wire across from the circuit beside it and the blower runs fine. I was coming to update the progress and ask where the wire comes from when I saw your post. I'd say a link is probably burned up. I'll look there next. I also noticed there is a 30A fuse for the heater. That seems awfully big. Might explain why the fusible link popped. I may be chasing a short next. Thanks for the help!
Bud

 

[HHhuntitall]

Wellllllll, if you look at the fusible links in the above pic, you'll notice one on the left is just a nub... . it's been soldered around in the black shrink-wrap to the right of the assembly with a new fusible link. Also, check the battery feed wire, making sure it has fire at the link. I've seen some that have burned up/corroded into so no fire would get to the instrument panel, key switch, and other problems. Good luck!



Let me add that this pic is of a late '92, so it may be a little different than your ealier truck, but very similar. If you have more problems, let me know, I've got a 91. 5 service manual in the shop.....

 

[BSeyler]

The picture is perfect and I have a better understanding of how it works. My concern is the 30A fuse -makes me think it was blowing the standard fuse, so someone added a larger one. I'll check the fusible links when I go back out. If it's blown, I think I'll put a jumper wire (with a fuse in case there's a short) to the lug on the fuse panel. I'm thinking it shouldn't be more than 10A or 15A to the heater, but don't have a manual that tells me. Our NAPA is pretty short on supply, but may be able to order one. I have to drive about 45 miles to a dealer now, thanks to Obama.

The nice thing about this pickup is that it is a one owner rig and the man who owned it left it pretty much stock. He added a flatbed at some point and hydraulics for a bale spear. It also is wired for a cake feeder. That's about the only added stuff I can see - it even has the stock air box. I think he just had a few cows, so it doesn't appear that he used this rig hard at all. Thanks for the help!

My son is coming home for R&R in February and I think I'll pick him up at the airport with his new CTD!

 

[BSeyler]

It did turn out to be the fusible link. Hopefully, NAPA can fix me up. Then, the task will be to figure out what made it blow. My multi-tester is only good for 10A, so this is an excuse to upgrade. Thanks for the help!

Bud

 

[HHhuntitall]

Good deal. I looked at the FSM, and it shows a 30amp fuse for the A/C and Heater Blower Motor..... The large connector, 6 guage, from the battery with the plastic connector about a foot down the line from the battery, it supplies the fusible link hub from there and the alternator, as well. By reading the 91 FSM, it show the front side of the hub where the battery and alternator come in, and out the back(towards firewall), it's 20guage red(fusible link?) to a 12 guage Pink, which feeds the ignition switch, which in turn, feeds the blower motor fuse, and so on. So looking at it, it looks like it's done the same as mine in the above pictures... ... I'd test it, of course, but it gives you an idea of where to start. If the fusible links are good, it's in between in either the bulkhead connector through the firewall or in the ignition switch itself.

 

[BSeyler]

Thanks for the help. I did find a bad fusible link, in fact the very one that was bad in the picture you posted. NAPA only had 18ga and bigger. They are ordering me some 20ga and it will be there in the morning.

The jumper wire with a 20A fuse that I put on temporarily worked fine on the 20 mile round trip to town - AC runs cold and the fuse did not blow. Still might be a short if I hit the right bump, but I'll have to see on that.

I put a new ignition switch in last night - my wife gives me a hard time about having a complete hardware and automotive store in my shop, but it sure is handy.

I'm still a little baffled as to why there was no power to the blower switch, but the AC compressor would engage. With the engine off and ignition switch on, I can push the AC controls on the dash, as well as defrost, and hear the clutch. It'll be interesting to see what happens tomorrow.

 

[Nyoest]

When you select defrost it automatically runs the ac comp, I believe to remove moisture from the cabin.

 

[BSeyler]

Took it for a drive to my daughter's tonight, about 55 miles round trip. Seems the new ignition switch took care of the intermittent wait to start light and no OD lockup issue. I have a temporary jumper (with a 20A in-line fuse) from the battery to the fuse panel. The blower and AC work correctly. Planning to replace a fusible link tomorrow. The more I drive the pickup, the more I like it!

 

[HHhuntitall]

Thanks for the help. I did find a bad fusible link, in fact the very one that was bad in the picture you posted. NAPA only had 18ga and bigger. They are ordering me some 20ga and it will be there in the morning.



The jumper wire with a 20A fuse that I put on temporarily worked fine on the 20 mile round trip to town - AC runs cold and the fuse did not blow. Still might be a short if I hit the right bump, but I'll have to see on that.



I put a new ignition switch in last night - my wife gives me a hard time about having a complete hardware and automotive store in my shop, but it sure is handy.



I'm still a little baffled as to why there was no power to the blower switch, but the AC compressor would engage. With the engine off and ignition switch on, I can push the AC controls on the dash, as well as defrost, and hear the clutch. It'll be interesting to see what happens tomorrow.

A/C compressor relay is actuated by power from the switches in the dash control..... the blower motor power is independent, as it's such a large draw. As for the fusible link, it seems sometimes they just give way. The truck in the pic was replaced, and I thought it might be the blower motor was going bad, but it's been another 195K and no more problems..... go figure?!?!? But watch it anyway. If it does it again, the blower motor or motor resistor is going bad, probably, although it could be a short, I'd wager against it, as it's not blowing the fuse.

 

[Bluebird]

Chasing gremlins/Honor military: men, women

Good job Dad on selecting a CTD for your son.

Great posts and useful informantion and instructions for getting through the heater/AC system.



I honor your son for his service for our Freedom and the continued success of the USA. My son-in-law, USMC may return to the desert in February.



Patrick

 

[BSeyler]

Patrick,

I agree, very well detailed explanation. Kudos to HHhuntitall and Nyoest!

Thank you for the kind words on my son. Between him, two of our daughters, and a son in law, this makes deployment number six for our little brood. Good luck to you son in law and we'll be praying for his safe return.

Bud

 

[HHhuntitall]

Hats off to a sixth deployment. I've got friends back and forth, one about to depart next month, four over there right now..... they're lifer's and feel like they are making a difference. Sounds like your clan is, too.



God bless you and yours,