I think I remember labeling those shots as '91's because the numbers didn't fit neatly into any other years known ranges...process of elimination. :)

E389172 is within a known 1992 E-plate range

E389632 has no records but several before and after have records, and they're all for Dodge vehicles.

I'm afraid unless we hit on some definite 1991 Mustang E-plate records, 1992 is about as far back as we're going to be able to find records for.

Now here's an interesting plate not in any of the known ranges:

http://media.fotki.com/1_p,rsgtrfdts...SC06029-vi.jpg

Here's another shot of it from The California Highway Patrolman magazine:

http://media.fotki.com/1_p,wrfwbskkg...sionSSP-vi.jpg

Note the older, straight leg "R" on the deck lid lettering.

I looked up smog history on E436751 and no record found but went back 30 numbers and found all 1991 pickups and utilities starting at E436750. Went forward the same and found all 1992 pickups and utilities starting at E436766. Based on that and it being surrounded by 1991 Crown Vics, I'm guessing this one is a 1991 also. As the possible prototype car for this modification it appears to have been outfitted and plated outside of any other Mustang group. The rest of the lightbar equipped test Mustangs were 1992s most likely produced in a batch from the photos of them I've seen so far (E895220, E895228, E895229).

I'll have to dig through my CHP magazines to find the date of the one I scanned the second shot above from.

I have a '92 CHP coupe with "9186" painted on the inside of the door. There's also an old punch-style sticker on the dash with the same number and another that says "stall 3."
I'd love to find out where it was stationed. Thanks to this thread I think I know what the plate might have been!
Not that it helps, but I bought the car in the San Fernando Valley and supposedly that's where it was bought at the CHP auction as well.

Sorry, quick question. If '92 plates go through 9189, is it safe to assume that my car was a late addition to the fleet in '92 since it's car number 9186?
Also, I see there are two different number sets and that may be for NorCal and SoCal cars. Can any of the pros shed some light on whether or not my car may have been in service in SoCal or not?
I'd sure love to find out where it was stationed!

Sorry to blow the thread up. I bought a Marti report and found this info on there:
720002 San Francisco Ordering District under Domestic
Special Order # 0002

and

ORDER TYPE: FLEET
DSO ITEM #: 8166
DEALER #: 72U511
RON DUPRATT FORD
1320 N FI RST ST
DIXON CA 95620

I don't know if that helps at all with the plate research info, but I thought I might share. And if any of the SSP pros can help shed any info on this stuff, I'm all ears. I wonder if this means my car was actually a Northern California car?

DSO 72 = San Jose ordering district

While there are certain plate number ranges associated with certain build years, plates themselves were not assigned in strict numerical order within build years.

The most definitive document to establish where a unit was stationed is the CHP Assignment Card which is hard to impossible to obtain. You may get lucky if an in-service photo or some other agency documentation can be found to associate the unit to a location. Otherwise, it can be tough to establish this information.

Justin, Swis bought the car at an auto auction in Van Nuys on Van Nuys Bl. across the street from the old GM plant. I believe the car had been repo'd from the previous owner.

Would you please post a picture of the tag on the dash. I want to see the location and the font style used plus the width of the tape. I need to make a couple for my CHP cars as well.